Chemical Composition, Toxicity, and Repellency of Essential Oils from Three Hedychium Species Against Stored-Product Insects

Stored products are constantly infested by insects, so finding eco-friendly bioinsecticides for insect management is important. The work aimed to assess the insecticidal and repellent activity of essential oil (EO) from Hedychium glabrum S. Q. Tong, Hedychium coronarium Koen., and Hedychium yunnanense Gagnep. against Tribolium castaneum, Lasioderma serricorne, and Liposcelis bostrychophila. Results showed that 88 chemical components were identified in the extracted Hedychium EOs, indicating that they exhibited diversity in components. According to principal component analysis (PCA), the composition of the EO from the H. yunnanense stem and leaf (EOHYSL) was significantly different from other EOs due to the different organs and species. The biological activity also varied continuously with plant species and organs. Only the EO of H. yunnanense (EOHY) showed strong fumigant toxicity. While in the contact tests, EOHGR showed the strongest toxicity effect on L. bostrychophila, with a LC50 value of 71.76 μg/cm2, which was closest to the positive control (Pyrethrin). All EOs had remarkable repellent activities against the three target insects, and repellency increased with concentration. According to the results of the comprehensive score, EOHY had the highest potential, which ranged from 0.7999 to 0.8689. Thus, Hedychium EOs possess potential biorational traits to be biological insecticides.

Rational design, synthesis and binding mechanisms of novel benzyl geranate derivatives as potential eco-friendly aphid repellents

BACKGROUND

The push-pull strategy is considered as a promising eco-friendly method for pest management. Plant volatile organic compounds (PVOCs) act as semiochemicals constitute the key factor in implementing this strategy. Benzyl alcohol and geraniol, as functional PVOCs, were reported to regulate insect behavior, showing the potential application in pest control. Using geraniol as lead, a geraniol derivative 5i with fine repellent activity was discovered in our previous work. In order to explore novel, eco-friendly aphid control agents, a series of benzyl geranate derivatives was designed and synthesized using 5i as the lead and benzyl alcohol as the active fragment.

RESULTS

Benzyl alcohol was firstly evaluated to have repellent activity to Acyrthosiphon pisum. Based on this repellent fragment, a series of novel benzyl geranate derivatives was rationally designed and synthesized using a scaffold-hopping strategy. Among them, compound T9, with a binding affinity (Kd  = 0.43 μm) and a substantial repellency of 64.7% against A. pisum, is the most promising compound. Molecule docking showed that hydrophobic and hydrogen-bonding interactions substantially influenced the binding affinity of compounds with ApisOBP9. Additionally, T9 exhibited low-toxicity to honeybees and ladybugs.

CONCLUSION

Using a simple scaffold-hopping strategy combined with active fragment benzyl alcohol, a new derivative T9, with high aphid-repellency and low-toxicity to nontarget organisms, can be considered as a novel potential eco-friendly aphid control agent for sustainable agriculture. © 2023 Society of Chemical Industry.

The Odorant Receptor Recognizing Camphor in a Camphor Tree Specialist Orthaga achatina (Lepidoptera: Pyralidae)

Camphor has been used as an effective repellent and pesticide to stored products for a long history, but Orthaga achatina (Lepidoptera: Pyralidae) has evolved to specifically feed on the camphor tree Cinnamomum camphora. However, the behavioral response of O. achatina to camphor and the molecular basis of camphor perception are totally unknown. Here, we demonstrated that both male and female adults were behaviorally attracted to camphor, suggesting the adaptation of O. achatina to and utilization of camphor as a signal of C. camphora. Second, in 40 O. achatina OR genes obtained by analyzing antenna transcriptomes, only OachOR16/Orco significantly responded to camphor in the Xenopus oocyte system. Finally, by molecular docking analysis and site-directed mutagenesis, the Ser209 residue is confirmed to be essential for binding of the oachOR16 with camphor. This study not only reveals the camphor-based host plant choice and olfactory mechanisms of O. achatina but also provides a molecular target for screening more potential insect repellents.

Development of terpenoid repellents against Aedes albopictus: a combined study of biological activity evaluation and computational modelling

To explore novel terpenoid repellents, 22 candidate terpenoid derivatives were synthesized and tested for their electroantennogram (EAG) responses and repellent activities against Aedes albopictus. The results from the EAG experiments revealed that 5-(2-hydroxypropan-2-yl)-2-methylcyclohex-2-en-1-yl formate (compound 1) induced distinct EAG responses in female Aedes albopictus. At concentrations of 0.1, 1, 10, 100, and 1000 mg/L, the EAG response values for compound 1 were 179.59, 183.99, 190.38, 193.80, and 196.66 mV, demonstrating comparable or superior effectiveness to DEET. Repellent activity analysis indicated significant repellent activity for compound 1, closest to the positive control DEET. The in silico assessment of the ADMET profile of compound 1 indicates that it successfully passed the ADMET evaluation. Molecular docking studies exhibited favourable binding of compound 1 to the active site of the odorant binding protein (OBP) of Aedes albopictus, involving hydrophobic forces and hydrogen bond interactions with residues in the OBP pocket. The QSAR model highlighted the influential role of hydrogen-bonding receptors, positively charged surface area of weighted atoms, polarity parameters of molecules, and maximum nuclear-nuclear repulsion force of carbon-carbon bonds on the relative EAG response values of the tested compounds. This study holds substantial significance for the advancement of new terpenoid repellents.

Repellency and Toxicity of Vapor-Active Benzaldehydes against Aedes aegypti

Chemical screening efforts recently found that 3-phenoxybenzaldehyde, a breakdown product of alpha-cyano pyrethroids, was a potent spatial repellent against Aedes aegypti mosquitoes in a glass tube repellency assay. In order to characterize this molecule further and identify structure-activity relationships, a set of 12 benzaldehyde analogues were screened for their repellency and toxicity in vapor phase exposures at 100 μg/cm2. Dose-response analyses were performed for the most active compounds in order to better characterize their repellent potency and toxicity compared to those of other commercially available toxicants. The three most toxic compounds (LC50 values) were 3-chlorobenzaldehyde (CBA) (37 μg/cm2), biphenyl-3-carboxaldehyde (BCA) (48 μg/cm2), and 3-vinylbenzaldehyde (66 μg/cm2), which makes them less toxic than bioallethrin (6.1 μg/cm2) but more toxic than sandalwood oil (77 μg/cm2), a repellent/toxic plant essential oil. The most repellent analogues with EC50 values below 30 μg/cm2 were 3-phenoxybenzaldehyde (6.3 μg/cm2), isophthalaldehyde (23 μg/cm2), BCA (17 μg/cm2), and CBA (22 μg/cm2), which makes them about as active as N,N-diethyl-3-methylbenzamide (25.4 μg/cm2). We further investigated the activity of a select group of these benzaldehydes to block the firing of the central nervous system of A. aegypti larvae. Compounds most capable of repelling and killing mosquitoes in the vapor phase were also those most capable of blocking nerve firing in the larval mosquito nervous system. The results demonstrate that benzaldehyde analogues are viable candidate repellent and insecticidal molecules and may lead to the development of future repellent and vapor toxic vector control tools.

Assessment of Contact Toxicity and Repellent Effects of Essential Oils from Piper Plants Piper yunnanense and Piper boehmeriifolium against Three Stored-Product Insects

Storage is a crucial part during grain production for the massive spoilage caused by stored product insects. Essential oils (EOs) of plant origin have been highly recommended to combating insects which are biodegradable and safe mode of action. Hence, to make the fullest use of natural resources, essential oils of different parts from Piper yunnanense (the whole part, PYW; fruits, PYF; leaves, PYL) and Piper boehmeriifolium (leaves, PBL) were extracted by steam distillation method in the present study. Gas chromatography-mass spectrometry (GC-MS) characterization revealed bicyclogermacrene (PYW), γ-muurolene (PYF), δ-cadinene (PYL) and methyl 4,7,10,13,16,19-docosahexaenoate (PBL) as the principal compound of each essential oil. Sesquiterpene hydrocarbons were also recognized as the richest class accounting for 56.3 %-94.9 % of the total oil. Three storage pests, Tribolium castaneum, Lasioderma serricorne and Liposceis bostrychophila, were exposed to different concentrations of EOs to determine their insecticidal effects. All tested samples performed modest contact toxicity in contrast to a bioactive ingredient pyrethrin, among which the most substantial effects were observed in PYF EOs against T. castaneum (35.84 μg/adult), PBL EOs against L. serricorne (15.76 μg/adult) and PYW EOs against L. bostrychophila (57.70 μg/cm2 ). In terms of repellency tests, essential oils of PYF at 78.63 nL/cm2 demonstrated to have a remarkable repellence against T. castaneum at 2h and 4h post-exposure. The investigations indicate diverse variations in the chemical profiles and insecticidal efficacies of P. yunnanense and P. boehmeriifolium EOs, providing more experimental evidence for the use of the Piper plants.

The essential oil of Kochia scoparia (L.) Schrad. as a potential repellent against stored-product insects

Chemical composition of the essential oil from Kochia scoparia (L.) Schrad. (syn. Bassia scoparia (L.) A. J. Scott) was analyzed in quality and quantity by GC-MS and GC-FID. Repellent activities of the essential oil from K. scoparia (KSEO) were evaluated against two common species of stored-product insects Tribolium castaneum Herbst and Liposcelis bostrychophila Badonnel. Results indicated that KSEO mainly consisted of eugenol, β-caryophyllene, and α-humulene, accounting for 75.6%, 8.2%, and 1.4% of the total oil, respectively. KSEO and the three major components were repellent to T. castaneum and L. bostrychophila adults. Notably, KSEO exerted significant effects, comparable to the positive control DEET at 2 and 4 h post-exposure. Eugenol at 63.17-2.53 nL/cm2 exhibited high percentage repellency ranging from 96 to 70% against L. bostrychophila during 4-h exposure. To gain further insights into the repellent activity, molecular docking simulation was performed with eugenol as the ligand and an odorant binding protein TcOBPC12 (gene: TcOBP10B) from the model insect T. castaneum as the receptor. Docking calculation results revealed that TcOBPC12 had binding affinity to eugenol (△G =  - 4.52 kcal/mol) along with a hydrogen bond of 0.18 nm (1.8 Å) long forming between them, which could be an important target protein associated with identifying volatile repellent molecules. This work highlights the promising potential of KSEO as a botanical repellent for controlling stored-product insects.

Structural Exploration of Novel Pyrethroid Esters and Amides for Repellent and Insecticidal Activity against Mosquitoes

The emergence of pyrethroid-resistant mosquitoes is a worldwide problem that necessitates further research into the development of new repellents and insecticides. This study explored the modification of existing pyrethroid acids to identify structural motifs that might not be affected by kdr active site mutations that elicit pyrethroid resistance. Because synthetic pyrethroids almost always contain activity-dependent chiral centers, we chose to focus our efforts on exploring alkoxy moieties of esters obtained with 1R-trans-permethrinic and related acids, which we showed in previous studies to have repellent and/or repellent synergistic properties. To this end, compounds were synthesized and screened for spatially acting repellency and insecticidal activity against the susceptible, Orlando, and pyrethroid-resistant, Puerto Rico, strains of Aedes aegypti mosquito. Screening utilized a high-throughput benchtop glass tube assay, and the compounds screened included a mixture of branched, unbranched, aliphatic, halogenated, cyclic, non-cyclic, and heteroatom-containing esters. Structure-activity relationships indicate that n-propyl, n-butyl, n-pentyl, cyclobutyl, and cyclopentyl substituents exhibited the most promising repellent activity with minimal kdr cross resistance. Preliminary testing showed that these small alcohol esters can be synergistic with phenyl amides and pyrethroid acids. Further derivatization of pyrethroid acids offer an interesting route to future active compounds, and while mosquitoes were the focus of this work, pyrethroid acids and esters have potential for use in reducing pest populations and damage in cropping systems as well.

Extraction and chemical characterisation of agro-waste from turmeric leaves as a source of bioactive essential oils with insecticidal and antioxidant activities

Turmeric (Curcuma longa L.) is a significant crop that has historically been used worldwide as a medicinal plant, spice, food colouring agent, and a significant ingredient in cosmetic industries. After harvesting rhizomes, leaves are considered waste material. This research study aims to extract and chemically characterise the essential oil from the leaves waste of turmeric with an evaluation of different insecticidal, antioxidant, and phytotoxic activities. Subsequently, the contact toxicity, fumigant toxicity, and repellent activity were evaluated against two key stored grain insect species. The gas chromatography-mass spectrometry (GC-MS) characterisation revealed that α-phellandrene (28.95%), 2-carene (16.51%), eucalyptol (10.54%) and terpinolene (10.24%) were the major chemical constituents. The study's findings on the insecticidal effects of essential oils extracted from turmeric leaves revealed noteworthy repellent, contact (at 24 h, LC50 = 6.51 mg/cm2 for Tribolium castaneum and LC50 = 4.74 mg/cm2 for Rhyzopertha dominica) and fumigant toxicities (at 24 h, LC50 = 2.57 mg/L air for T. castaneum and LC50 = 2.83 mg/L air for R. dominica), against two key stored grain insects. In addition, turmeric leaf essential oil showed notable antioxidant activity (IC50 = 10.04 ± 0.03 µg/mL for DPPH assay; IC50 = 14.12 ± 0.21 µg/mL for ABTS assay. Furthermore, a phytotoxicity study was carried out on stored paddy seeds and no toxic effects were found on germination rate and seedling growth. So, it might be expected that the essential oils extracted from the turmeric leaf waste could be valorised and demonstrate their potential as safe botanical insecticides against stored-product insects, with noble antioxidant properties.

Comparative Bioactivity Evaluation of Chemically Characterized Essential Oils Obtained from Different Aerial Parts of Eucalyptus gunnii Hook. f. (Myrtaceae)

Essential oils (EOs) obtained by hydro-distillation from different parts of twigs (EOT), leaves (EOL), and fruits (EOF) of Eucalyptus gunnii Hook. f. were screened for their chemical composition, insecticidal, repellence, and antibacterial properties. Based on GC and GC/MS analysis, 23 constituents were identified across the twigs, leaves, and fruits, with 23, 23, and 21 components, respectively. The primary significant class was oxygenated monoterpenes (82.2–95.5%). The main components were 1,8-cineole (65.6–86.1%), α-terpinyl acetate (2.5–7.6%), o-cymene (3.3–7.5%), and α-terpineol (3.3–3.5%). All three EOs exhibited moderate antibacterial activities. EOL was found to have higher antibacterial activity against all tested strains except Dickeya solani (CFBP 8199), for which EOT showed more potency. Globally, Dickeya solani (CFBP 8199) was the most sensitive (MIC ≤ 2 mg/mL), while the most resistant bacteria were Dickeya dadantii (CFBP 3855) and Pectobacterium carotovorum subsp. carotovorum (CFBP 5387). Fumigant, contact toxicity, and repellent bioassays showed different potential depending on plant extracts, particularly EOT and EOL as moderate repellents and EOT as a medium toxicant.

The structure of AgamOBP5 in complex with the natural insect repellents Carvacrol and Thymol: Crystallographic, fluorescence and thermodynamic binding studies

Among several proteins participating in the olfactory perception process of insects, Odorant Binding Proteins (OBPs) are today considered valid targets for the discovery of compounds that interfere with their host-detection behavior. The 3D structures of Anopheles gambiae mosquito AgamOBP1 in complex with the known synthetic repellents DEET and Icaridin have provided valuable information on the structural characteristics that govern their selective binding. However, no structure of a plant-derived repellent bound to an OBP has been available until now. Herein, we present the novel three-dimensional crystal structures of AgamOBP5 in complex with two natural phenolic monoterpenoid repellents, Carvacrol and Thymol, and the MPD molecule. Structural analysis revealed that both monoterpenoids occupy a binding site (Site-1) by adopting two alternative conformations. An additional Carvacrol was also bound to a secondary site (Site-2) near the central cavity entrance. A protein-ligand hydrogen-bond network supplemented by van der Waals interactions spans the entire binding cavity, bridging α4, α6, and α3 helices and stabilizing the overall structure. Fluorescence competition and Differential Scanning Calorimetry experiments verified the presence of two binding sites and the stabilization effect on AgamOBP5. While Carvacrol and Thymol bind to Site-1 with equal affinity in the submicromolar range, they exhibit a significantly lower and distinct binding capacity for Site-2 with Kd's of ~7 μΜ and ~18 μΜ, respectively. Finally, a comparison of AgamOBP5 complexes with the AgamOBP4-Indole structure revealed that variations of ligand-interacting aminoacids such as A109T, I72M, A112L, and A105T cause two structurally similar and homologous proteins to display different binding specificities.

Prolonged Repellent Activity of Plant Essential Oils against Dengue Vector, Aedes aegypti

Repellents are effective personal protective means against outdoor biting mosquitoes. Repellent formulations composed of EOs are finding increased popularity among consumers. In this study, after an initial screening of 11 essential oils (EOs) at the concentration of 33 μg/cm², five of the most repellent EOs, Perovskia atriplicifolia, Citrus reticulata (fruit peels), C. reticulata (leaves), Mentha longifolia, and Dysphania ambrosioides were further investigated for repellent activity against Aedes aegypti mosquitoes in time span bioassays. When tested at the concentrations of 33 μg/cm², 165 μg/cm² and 330 μg/cm², the EO of P. atriplicifolia showed the longest repellent effect up to 75, 90 and 135 min, respectively, which was followed by C. reticulata (peels) for 60, 90 and 120 min, M. longifolia for 45, 60 and 90 min, and C. reticulata (leaves) for 30, 45 and 75 min. Notably, the EO of P. atriplicifolia tested at the dose of 330 μg/cm² showed complete protection for 60 min which was similar to the commercial mosquito repellent DEET. Gas chromatographic-mass spectrometric analyses of the EOs revealed camphor (19.7%), limonene (92.7%), sabinene (24.9%), carvone (82.6%), and trans-ascaridole (38.8%) as the major constituents of P. atriplicifolia, C. reticulata (peels), C. reticulata (leaves), M. longifolia, and D. ambrosioides, respectively. The results of the present study could help develop plant-based commercial repellents to protect humans from dengue mosquitoes.

Experimental evaluation and structure-activity relationship analysis of bridged-ring terpenoid derivatives as novel Blattella germanica repellent

Cockroaches are urban pests that are very difficult to control. Using repellents is a green, safe and effective strategy for their control. In order to find novel cockroach repellents, the repellent activity of 45 bridged-ring terpenoid derivatives synthesized from β-pinene against Blattella germanica was tested. The relationship between the molecular structure of these bridged-ring terpenoid derivatives and their repellent activity against Blattella germanica was also analysed. The results show that some of the bridged-ring terpenoid derivatives exhibit good repellent activity against Blattella germanica, and six compounds (RR = 60.44-87.32%) show higher repellent activity against Blattella germanica than DEET (RR = 54.77%), making them promising for development as new cockroach repellents. Quantitative structure-activity relationship (QSAR) analysis revealed that the HOMO-1 energy, Kier and Hall index (order 2), Balaban index, and relative positive charged surface area of bridged-ring terpenoid derivatives have effects on repellent activity against Blattella germanica. The present study may provide a theoretical basis for the high-value use of β-pinene and can be helpful to the development of novel repellents against Blattella germanica.

Chemical Composition of Essential Oils from Three Rhododendron Species and Their Repellent, Insecticidal and Fumigant Activities

In order to assess the repellent, contact, and fumigant properties of three essential oils (EOs) from Rhododendron species in China against adults of Tribolium castaneum, Lasioderma serricorne, Sitophilus oryzae, this study analyzed their chemical components. The three EOs were extracted by hydrodistillation from leaves of Rhododendron species, including R. davidsonianum, R. heliolepis and R. strigillosum. Sesquiterpenoids and monoterpenes were the main components of the three EOs that were detected by GC/MS and GC-FID. α-Pinene, β-Caryophyllene, α-Humulene, Kaura-16-ene and Sandaracopimaradiene was among the comparatively high components. In this study, the EOs of three Rhododendron species demonstrated repellent activities against T. castaneum and L. serricorne in 2 h and 4 h exposure, but the repellent activity to S. oryzae was not obvious. The three EOs from R. davidsonianum, R. heliolepis and R. strigillosum also had contact activities and fumigant activities against the Tribolium castaneum (LC50 =13.453 mg/L air, 4.728 mg/L air, 4.529 mg/L air and LD50 =15.027 μg/adult, 15.017 μg/adult, 10.994 μg/adult, respectively), Lasioderma serricorne (LC50 =8.584 mg/L air, 6.044 mg/L air, 6.355 mg/L air and LD50 =4.566 μg/adult, 7.067 μg/adult, 3.652 μg/adult, respectively) and Sitophilus oryzae (LC50 =3.304 mg/L air, 6.795 mg/L air, 7.130 mg/L air and LD50 =10.200 μg/adult, 15.021 μg/adult, 9.178 μg/adult, respectively) adults. The above results not only opened a potential prospect for applications of Rhododendrons in the prevention and control of insects in stored products, but also provide a basis for the comprehensive utilization of the rich natural Rhododendron plant resources.

Repellency, contact toxicity, and anti-oviposition effects of three ethanol-extracted plant essential oils on Bemisia tabaci (Hemiptera: Aleyrodidae)

There are more than 1200 species of whiteflies found across the globe. Due to the high level of resistance of whitefly against synthetic insecticides, alternate pest management measures have their significance. Plant essential oils (EOs) affect insect pests in many ways, such as via stimulatory, deterrent, toxic, and hormonal effects. This study was designed to determine the repellency of EOs, toxicity, and oviposition deterrent activities of Allium ascalonicum, Cinnamomum camphora, and Mentha haplocalyx against adult whiteflies. In repellency determination experiments, a single tomato plant was treated with 10 ml of ethanol-extracted EO with 1000 ppm concentration. Results showed that C. camphora EO was the most repellent for whitefly compared to M. haplocalyx and A. ascalonicum. The oviposition deterrent experiments revealed that C. camphora has the highest oviposition deterrent effect, followed by M. haplocalyx and A. ascalonicum. A single plant treatment method was used to assess the contact toxicity of three EOs against whitefly after 12, 24, 48, and 72 h of exposure. The results revealed that C. camphora is more toxic to whitefly than M. haplocalyx and A. ascalonicum. After determining the antagonistic effects of these EOs, the oils were analyzed using gas chromatography/mass spectrometry to identify the chemical components. It can be concluded that C. camphora is the most effective oil EO in terms of toxicity, repellence, and oviposition deterrence, followed by M. haplocalyx and A. ascalonicum under greenhouse conditions. Our results introduce some new eco-friendly plant EOs to control whiteflies.

Insect repellent pellets - an application of botanicals against red flour beetle - their antifungal activity during storage and use as potential fumigants

BACKGROUND

The protection of grains from insect infestation is critical during storage. Insect repellent pellets (IRPs) are a potential technique to repel insects by hindering insect movement toward the grains. The basic principle of IRPs is the use of active components found in the oils of lemongrass, eucalyptus, and neem leaves for the controlled release of fumes, thereby avoiding the need for reapplication after a few days. Here, we examined the antifungal activity, the lethal dose, and the repelling effect of IRPs against red flour beetle, Tribolium castaneum, over a 30 day period.

RESULTS

We observed that IRPs possessed antifungal properties and were able to repel the adults of T. castaneum. These insects ultimately died from the fumes if they manage to stay near the IRPs (LD₅₀  = 2 and LD₉₉  = 7 days). The active components (phenol, 2,4-di-tert-butyl-, citral, neral, geraniol, n-hexadecanoic acid) present in IRP during the initial stage were also found after a storage period of 35 days.

CONCLUSION

The active components present in IRPs have antifungal, repellent, and fumigant properties. The IRPs can thus be termed potent botanical insecticides and are an alternative to synthetic insecticides. © 2022 Society of Chemical Industry.

Hierarchical Virtual Screening and Binding Free Energy Prediction of Potential Modulators of Aedes Aegypti Odorant-Binding Protein 1

The Aedes aegypti mosquito is the main hematophagous vector responsible for arbovirus transmission in Brazil. The disruption of A. aegypti hematophagy remains one of the most efficient and least toxic methods against these diseases and, therefore, efforts in the research of new chemical entities with repellent activity have advanced due to the elucidation of the functionality of the olfactory receptors and the behavior of mosquitoes. With the growing interest of the pharmaceutical and cosmetic industries in the development of chemical entities with repellent activity, computational studies (e.g., virtual screening and molecular modeling) are a way to prioritize potential modulators with stereoelectronic characteristics (e.g., pharmacophore models) and binding affinity to the AaegOBP1 binding site (e.g., molecular docking) at a lower computational cost. Thus, pharmacophore- and docking-based virtual screening was employed to prioritize compounds from Sigma-Aldrich® (n = 126,851) and biogenic databases (n = 8766). In addition, molecular dynamics (MD) was performed to prioritize the most potential potent compounds compared to DEET according to free binding energy calculations. Two compounds showed adequate stereoelectronic requirements (QFIT > 81.53), AaegOBP1 binding site score (Score > 42.0), volatility and non-toxic properties and better binding free energy value (∆G < −24.13 kcal/mol) compared to DEET ((N,N-diethyl-meta-toluamide)) (∆G = −24.13 kcal/mol).

Biological activities and gene expression of detoxifying enzymes in Tribolium castaneum induced by Moutan cortex essential oil

Tribolium castaneum is one of the most harmful storage pests in the world. The aim of this study was to determine the chemical composition, repellent, and contact activities of Moutan cortex essential oil against this insect pest. In addition, the effects of Moutan cortex were examined on the expressions of three major detoxifying enzyme genes in T. castaneum. Four components were identified in this essential oil by gas chromatography-mass spectrometry (GC-MS), which was predominantly paeonol (99.13%). Paeonol exerted significant repellent activity against T. castaneum, which was more potent than the positive control N.N-diethyl-meta-toluamide (DEET). The most significant contact toxicity was observed at 24 h after exposure to paeonol. Further, quantitative real-time PCR (qRT-PCR) was used to assess expression changes in three detoxification enzyme genes in T. castaneum, including carboxylesterase (CarE), glutathione S-transferase (Gst) and cytochrome P4506BQ8 (Cyp6bq8). Among these, Gst was most highly up-regulated after treatment with paeonol with the highest expression level of 4.9-fold (Rps18 as internal reference gene) greater than control at 24 h following treatment. Data indicated that Gst might play a critical role in metabolic detoxification of toxic xenobiotics. Taken together, our findings might lay a foundation for development of paeonol as a potential natural repellent or pesticide to control storage pests.

N,N-Diethyl-3-toluamide Formulation Based on Ethanol Containing 0.1% 2-Hydroxypropyl-β-cyclodextrin Attenuates the Drug's Skin Penetration and Prolongs the Repellent Effect without Stickiness

N,N-diethyl-3-toluamide (DEET) is one of the most widely used insect repellents in the world. It was reported that a solution containing 6-30% cyclodextrin (CD) as a solvent instead of ethanol (EtOH) provided an enhancement of the repellent action time duration of the DEET formulation, although the high-dose CD caused stickiness. In order to overcome this shortcoming, we attempted to prepare a 10% DEET formulation using EtOH containing low-dose CDs (β-CD, 2-hydroxypropyl-β-CD (HPβCD), methyl-β-CD, and sulfobutylether-β-CD) as solvents (DEET/EtOH/CD formulations). We determined the CD concentration to be 0.1% in the DEET/EtOH/CD formulations, since the stickiness of 0.1% CDs was not felt (approximately 8 × 10^-3 N). The DEET residue on the skin superficial layers was prolonged, and the drug penetration into the skin tissue was decreased by the addition of 0.1% CD. In particular, the retention time and attenuated penetration of DEET on the rat skin treated with the DEET/EtOH/HPβCD formulation was significantly higher in comparison with that of the DEET/EtOH formulation without CD. Moreover, the repellent effect of DEET was more sustained by the addition of 0.1% HPβCD in the study using Aedes albopictus. In conclusion, we found that the DEET/EtOH/HPβCD formulations reduced the skin penetration of DEET and prolonged the repellent action without stickiness.

Mosquito Repellent Potential of Carpesium abrotanoides Essential Oil and Its Main Components Against a Dengue Vector, Aedes aegypti (Diptera: Culicidae)

Disease vectoring mosquitoes are a serious threat to humans. However, till today only few mosquito repellents have been identified. The current study was conducted to evaluate the repellent potential of Carpesium abrotanoides essential oil against Aedes aegypti females by human bait technique. Essential oil was extracted by steam distillation process while the identification of chemical constituents was carried out by gas chromatography-mass spectrometry. Time span repellent bioassays of C. abrotanoides essential oil in comparison to DEET were performed at three different doses (33 μg/cm2, 165 μg/cm2, and 330 μg/cm2) under laboratory conditions. Highest repellency periods for essential oil and DEET were observed at the tested dose of 330 μg/cm2 with 315 min and 720 min, respectively. Lowest repellency period of 45 min for essential oil and 105 min for DEET was recorded at the tested dose of 33 μg/cm2. Major constituents caryophyllene (24.3%) and trans-nerolidol (12.0%) of C. abrotanoides essential oil were also evaluated as repellents at three different doses (330 μg/cm2, 165 μg/cm2, and 33 μg/cm2) against Ae. aegypti. Surprisingly, trans-nerolidol completely inhibited Ae. aegypti landings for 45 min when tested at 330 μg/cm2. However, caryophyllene did not completely inhibit Ae. aegypti landing even after immediate application at the tested dose of 330 μg/cm2. At the tested dose of 330 μg/cm2, the mixture (trans-nerolidol + caryophyllene) completely inhibited Ae. aegypti landing for 60 min indicating the synergistic effect of caryophyllene. Hence, C. abrotanoides as well as its major constituent, especially trans-nerolidol, have potential to formulate as mosquito repellent comparable of DEET.

Host-Guest Inclusion Complexes of Natural Products and Nanosystems: Applications in the Development of Repellents

Repellents are compounds that prevent direct contact between the hosts and the arthropods that are vectors of diseases. Several studies have described the repellent activities of natural compounds obtained from essential oils. In addition, these chemical constituents have been pointed out as alternatives to conventional synthetic repellents due to their interesting residual protection and low toxicity to the environment. However, these compounds have been reported with short shelf life, in part, due to their volatile nature. Nanoencapsulation provides protection, stability, conservation, and controlled release for several compounds. Here, we review the most commonly used polymeric/lipid nanosystems applied in the encapsulation of small organic molecules obtained from essential oils that possess repellent activity, and we also explore the theoretical aspects related to the intermolecular interactions, thermal stability, and controlled release of the nanoencapsulated bioactive compounds.

In silico prediction of mosquito repellents for clothing application

Use of protective clothing is a simple and efficient way to reduce the contacts with mosquitoes and consequently the probability of transmission of diseases spread by them. This mechanical barrier can be enhanced by the application of repellents. Unfortunately the number of available repellents is limited. As a result, there is a crucial need to find new active and safer molecules repelling mosquitoes. In this context, a structure-activity relationship (SAR) model was proposed for the design of repellents active on clothing. It was computed from a dataset of 2027 chemicals for which repellent activity on clothing was measured against Aedes aegypti. Molecules were described by means of 20 molecular descriptors encoding physicochemical properties, topological information and structural features. A three-layer perceptron was used as statistical tool. An accuracy of 87% was obtained for both the training and test sets. Most of the wrong predictions can be explained. Avenues for increasing the performances of the model have been proposed.

Chirality Effects on Repellent Properties of 4-Alkoxycoumarins Against Asian Tiger Mosquito (Diptera: Culicidae)

The use of semiochemicals as repellents and attractants has been proposed to complement insecticides used for the control of vector mosquito populations. In several studies, the optical purities of the molecules tested have been described as having little or no effect on repellent activity. However, these observations seem difficult to explain because of the chirality effect of molecules on the olfactory system of insects and humans. Thus, the purpose of this study is to assess the effects of chirality on the repellent properties of 4-alcoxycoumarins against Aedes albopictus Skuse, mosquito vector of arboviruses. We report here that the racemic (R/S)-4-sec-butoxycoumarin had the highest repellent effect (Repellent Index = 49.9%) followed by (R) enantiomer (Repellent Index = 24.2%) for the dose of 5 mg/mL. Contrary, no significant repellent activity was recorded for S-(+)-4-sec-butoxycoumarin. This experiment demonstrates the close relationship between the molecules' optical purities and the behavioral response of mosquitoes.

The fabrication and assessment of mosquito repellent cream for outdoor protection

Mosquito-borne infections like dengue, malaria, chikungunya, etc. are a nuisance and can cause profound discomfort to people. Due to the objectional side effects and toxicity associated with synthetic pyrethroids, N,N-diethyl-3-methylbenzamide (DEET), N,N-diethyl phenylacetamide (DEPA), and N,N-di ethyl benzamide (DEBA) based mosquito repellent products, we developed an essential oil (EO) based mosquito repellent cream (EO-MRC) using clove, citronella and lemongrass oil. Subsequently, a formulation characterization, bio-efficacy, and safety study of EO-MRC were carried out. Expression of Anti-OBP2A and TRPV1 proteins on mosquito head parts were studied by western blotting. In-silico screening was also conducted for the specific proteins. An FT-IR study confirmed the chemical compatibility of the EOs and excipients used in EO-MRC. The thermal behaviour of the best EOs and their mixture was characterized by thermogravimetric analysis (TGA). GC-MS examination revealed various chemical components present in EOs. Efficacy of EO-MRC was correlated with 12% N,N-diethyl benzamide (DEBA) based marketed cream (DBMC). Complete protection time (CPT) of EO-MRC was determined as 228 min. Cytotoxicity study on L-132 cell line confirmed the non-toxic nature of EO-MRC upon inhalation. Acute dermal irritation study, acute dermal dose toxicity study, and acute eye irritation study revealed the non-toxic nature of EO-MRC. Non-target toxicity study on Danio rerio confirmed EO-MRC as safer for aquatic non-target animals. A decrease in the concentration of acetylcholinesterase (AChE) was observed in transfluthrin (TNSF) exposed Wistar rats. While EO-MRC did not alter the AChE concentrations in the exposed animals. Results from western blotting confirmed that Anti-OBP2A and TRPV1 proteins were inhibited in TNSF exposed mosquitoes. Mosquitoes exposed to EO-MRC showed a similar expression pattern for Anti-OBP2A and TRPV1 as the control group. In silico study revealed eight identified compounds of the EOs play significant roles in the overall repellency property of the developed product. The study emphasizes the mosquito repellent activity of EO-MRC, which could be an effective, eco-friendly, and safer alternative to the existing synthetic repellents for personal protection against mosquitoes during field conditions.

Isolation, screening and identification of key components having intense insect repellent activity against Plodia interpunctella from four different medicinal plant materials

BACKGROUND

Global warming and the indiscriminate use of pesticides have increased the propagation of the stored-product insect pests, leading to enormous losses in the agriculture and food industries. The most used insect repellents are synthetic derivatives; however, these have an adverse effect on human health as well as on the environment. Therefore, we attempted to find materials with insect repellent activity in natural products. The present study aimed to identify the single chemical component with intense insect repellent activity in extracts from four different Oriental medicinal plant materials: (i) Anethum graveolens L. (dill) seeds; (ii) Artemisia capillaris Thunb. (capillary wormwood) leaves; (iii) smoked Prunus mume Siebold & Zucc. (mume) fruits; and (iv) Rhus javanica L. (galls).

RESULTS

As a result of the bioassay-guided fractionation of each extract against the Plodia interpunctella, stored-product insect, the n-hexane fraction of dill seeds extract was confirmed as the optimal fraction between all of the fractions. In total, 32 chemical components were identified from the n-hexane fraction of dill seeds by gas chromatography-mass spectrometry analysis, and the two main components were dillapiole (47.51%) and carvone (26.76%). Of the two components, dillapiole was confirmed as the key component playing an essential role in insect repellent activity.

CONCLUSION

Our study suggests that dillapiole has the potential to be used as a natural insect repellent for the control of P. interpunctella infestation in agricultural and food products during distribution and storage. © 2021 Society of Chemical Industry.

Semiochemical signatures associated with differential attraction of Anopheles gambiae to human feet

BACKGROUND

Several human-produced volatiles have been reported to mediate the host-seeking process under laboratory conditions, yet no effective lure or repellent has been developed for field application. Previously, we found a gradation of the attractiveness of foot odors of different malaria free individuals to Anopheles gambiae sensu stricto Giles. In this study, foot odor of the individual with the most attractive 'smelly' feet to the An. gambiae was collected, analyzed and attractive blend components identified.

METHODS

The foot odor of the individual with the most attractive 'smelly' feet to the An. gambiae was trapped on Porapak Q and analyzed by gas chromatography-linked mass spectrometry (GC-MS). Specific constituents perceived by the insect olfactory system were then identified by GC-linked to electro-antennography detector (GC-EAD) and characterized by GC-MS. The contribution of each constituent to the behavioral response of An. gambiae was assessed through subtractive assays under semi-field conditions in a screen-house using Counter Flow Geometry (CFG traps) baited with (i) the blend of all the EAD-active and (ii) other blends containing all components with exclusion of one component at a time. The number of mosquitoes trapped in the baited CFG traps were compared with those in the control traps.

RESULTS

Eleven major and minor constituents: 2 carboxylic acids, six aldehydes, two ketones and one phenolic compound, were confirmed to be EAD-active. The contribution of each constituent to the behavioral response of An. gambiae was assessed through subtractive assays under semi- field conditions. Exclusion/ subtraction of one of the following compounds: i-butyric acid, i-valeric acid, n-octanal, n-nonanal, n-decanal, n-dodecanal, undecanal or n-tridecanal, from each blend led to reduction in the attractiveness of all the resulting blends, suggesting that all of them are critical/important for the attractiveness of the foot odor to An. gambiae mosquitoes. However, exclusion/subtraction of 4-ethoxyacetophenone, 4-ethylacetophenone and/or 2-methylphenol, led to significant enhancements in the attractiveness of the resulting blends, suggesting that each of these compounds had repellent effect on An. gambiae ss. Undecanal exhibited kairomonal activity at low natural concentrations under semi-field conditions but repellent activity at high unnatural conditions in the laboratory. Furthermore, the comparison of the mean mosquito catches in traps baited with the nine-component blend without 4-ethoxyacetophenone, 4-ethylacetophenone and the complete foot odor collection revealed that the former is significantly more attractive and confirmed the repellent effect of the two carbonyl compounds at low natural concentration levels.

CONCLUSION

These results suggest that differential attractiveness of An. gambiae to human feet is due to qualitative and/or qualitative differences in the chemical compositions of the foot odors from individual human beings and relative proportions of the two chemical signatures (attractants versus repellents) as observed from the ratios of the bioactive components in the foot odors of the most attractive and least attractive individuals. Chemical signature means the ensemble of the compounds released by the organism in a specific physiological state. The chemical signature is emitter-dependent, but does not depend on receiver response. Thus, there is only one chemical signature for one individual or species that may eventually include inactive, attractive and repellent components for another organism. The nine-component attractive blend has a potential as an effective field bait for trapping of malaria vectors in human dwellings.

Analysis of chemical compositions and larvicidal activity of nut extracts from Areca catechu Linn against Aedes (Diptera: Culicidae)

Background

There is a growing need to use green alternative larvicidal control for Aedes larvae compared to chemical insecticides. Substantial reliance on chemical insecticides caused insecticide resistance in mosquito populations. Thus, research for alternate chemical compounds from natural products is necessary to control Aedes larvae. This study explores the analysis of chemical compositions from Areca catechu nut as a potential larvicide for Aedes (Diptera: Culicidae).

Methods

The Areca catechu nut collected from Ipoh, Perak, Malaysia was grounded into powder and used for Soxhlet extraction. The chemical analysis of the extracts and their structures were identified using the GCMS-QP2010 Ultra (Shimadzu) system. National Institute of Standards and Technology (NIST) Chemistry WebBook, Standard Reference Database 69 (https://webbook.nist.gov/chemistry/) and PubChem (https://pubchem.ncbi.nlm.nih.gov/), the two databases used to retrieve the synonyms, molecular formula, molecular weight, and 2-dimensional (2D) structure of chemical compounds. Next, following WHO procedures for larval bioassays, the extracts were used to asses larvicidal activity against early 4^th instar larvae of Aedes aegypti and Aedes albopictus.

Results

The larvicidal activities were observed against early 4^th stage larvae with different concentrations in the range from 200 mg/L to 1600 mg/L. The LC₅₀ and LC₉₅ of Aedes aegypti were 621 mg/L and 2264 mg/L respectively; whereas the LC₅₀ and LC₉₅ of Aedes albopictus were 636 mg/L and 2268 mg/L respectively. Mortality was not observed in the non-target organism test. The analysis using gas chromatography and mass spectrometer recovered several chemical compounds such as Arecaidine, Dodecanoic acid, Methyl tetradecanoate, Tetradecanoic acid <n->, and n-Hexadecanoic acid bioactive components. These chemical constituents were used as additive formulations in pesticides, pest control, insect repellent, and insecticidal agents.

Conclusions

Our study showed significant outcomes from the extract of Areca catechu nut and it deserves further investigation in relation to chemical components and larvicidal actions between different species of Aedes mosquitoes. Even though all these findings are fundamental, it may have some interesting potentials to be developed as natural bio-larvicidal products.

Insecticidal, Repellent and Antifeedant Activity of Essential Oils from Blepharocalyx cruckshanksii (Hook. & Arn.) Nied. Leaves and Pilgerodendron uviferum (D. Don) Florin Heartwood against Horn Flies, Haematobia irritans (Diptera: Muscidae)

Haematobia irritans is a cosmopolitan obligate blood-feeding ectoparasite of cattle and is the major global pest of livestock production. Currently, H. irritans management is largely dependent on broad-spectrum pesticides, which has led to the development of insecticide resistance. Thus, alternative control methods are needed. Essential oils have been studied as an alternative due to their wide spectrum of biological activities against insects. Thus, the main aim of this study was to evaluate the insecticidal, repellent and antifeedant activity of the essential oils from Blepharocalyx cruckshanksii leaves and Pilgerodendron uviferum heartwood against horn flies in laboratory conditions. The composition of the essential oils was analyzed using gas chromatography coupled to mass spectrometry. Accordingly, α-pinene (36.50%) and limonene (20.50%) were the principal components of the B. cruckchanksii essential oil, and δ-cadinol (24.16%), cubenol (22.64%), 15-copaenol (15.46%) and δ-cadinene (10.81%) were the most abundant compounds in the P. uviferum essential oil. Mortality of flies and feeding behavior were evaluated by non-choice tests, and olfactory response was evaluated using a Y-tube olfactometer. Both essential oils were toxic to horn flies, with LC50 values for B. cruckchanksii essential oil of 3.58 µL L-1 air at 4 h, and for P. uviferum essential oil of 9.41 µL L-1 air and 1.02 µL L-1 air at 1 and 4 h, respectively. Moreover, the essential oils exhibited spatial repellency in the olfactometer using only 10 µg of each oil, and these significantly reduced the horn fly feeding at all doses evaluated. Although further laboratory and field studies related to the insectistatic and insecticide properties of these essential oils against H. irritans are necessary, B. cruckshanksii leaves and P. uviferum heartwood essential oils are promising candidates for horn fly management.

Evaluation of a Novel User-Friendly Arthropod Repellent Gel, Verdegen

Hand sanitizers are developed as alcohol-based liquid gel formulations, generally used to decrease the amount of infectious agents on human hands. Verdegen, LLC proposed to prepare an arthropod repellent gel for public use when the recent outbreaks of Zika infection vectored through Aedes mosquitoes in the American continents prompted multi-faceted emergency measures. Four different gel formulations were developed, comprising two of the most efficacious commercial arthropod repellent active ingredients, N,N-diethyl-3-methyl benzamide (deet) and 2-(2-hydroxyethyl)-1-piperidinecarboxylic acid 1-methylpropyl ester (picaridin), each at different concentrations (20 and 33% deet, or 20 and 33% picaridin). Compliance with the use of topical arthropod repellents remains an issue among military personnel. One of the most common complaints by Soldiers is that they do not like how the repellents applied on their skin leave behind an oily or greasy residue. These new gel formulations offer a user-friendly alternative for commonly used arthropod repellents formulations for the military and civilian personnel. We tested the efficacy and protection time of these new gel formulations in comparison with the commercially available cream formulations of deet and picaridin at similar concentrations. Our data show that gel formulations have better topical attributes, and offer equal or better biting protection for up to 48 h against host-seeking Aedes aegypti (L.) (Diptera: Culicidae) female mosquitoes.

Chemical Composition of Cinnamomum verum Leaf and Flower Essential Oils and Analysis of Their Antibacterial, Insecticidal, and Larvicidal Properties

Cinnamomum verum is widely used in traditional medicines, and the different parts of the plant, such as bark, leaves, and flowers, are used for essential oil production. The present study compared the chemical composition of the essential oil of C. verum extracted from the leaves and flowers. In addition, efficacy of these essential oils against the two common pests Sitophilus oryzae and Callosobruchus maculatus was also evaluated. The results indicated the presence of cinnamaldehyde, eugenol, caryophyllene, and linalool in these essential oils, however, at different concentrations. The leaf essential oil was found to be 10-20% more effective as a fumigant against both the pests. Likewise, the leaf essential oil found to repel these pests even at lower concentrations than that of flower essential oil of C. verum. Besides, these essential oils were also effective in controlling the growth of various gram positive and gram negative microbial pathogens and possibly a safeguard for human health. On contrary, both the essential oils were found to be safe for the application on grains, as indicated by their germination potentials. It was also observed that these essential oils do not cause any significant toxicity to guppy fishes, thus confirming their ecological safety for use as a biopesticide.

Properties of Mosquito Repellent-Plasticized Poly(lactic acid) Strands

Poly(lactic acid) (PLA) is an attractive candidate for replacing petrochemical polymers because it is fully biodegradable. This study investigated the potential of PLA as a sustainable and environmentally friendly alternative material that can be developed into commercially viable wearable mosquito repellent devices with desirable characteristics. PLA strands containing DEET and IR3535 were prepared by twin screw extrusion compounding and simultaneously functioned as plasticizers for the polymer. The plasticizing effect was investigated by thermal and rheological studies. DSC studies showed that the addition of DEET and IR3535 into PLA strands reduced the glass transition temperature consistent with predictions of the Fox equation, thus proving their efficiency as plasticizers. The rheology of molten samples of neat PLA and PLA/repellents blends, evaluated at 200 °C, was consistent with shear-thinning pseudoplastic behaviour. Raman studies revealed a nonlinear concentration gradient for DEET in the PLA strand, indicating non-Fickian Type II transport controlling the desorption process. Release data obtained at 50 °C showed initial rapid release followed by a slower, near constant rate at longer times. The release rate data were fitted to a novel modification of the Peppas-Sahlin desorption model.

Sodium channel activation underlies transfluthrin repellency in Aedes aegypti

Background

Volatile pyrethroid insecticides, such as transfluthrin, have received increasing attention for their potent repellent activities in recent years for controlling human disease vectors. It has been long understood that pyrethroids kill insects by promoting activation and inhibiting inactivation of voltage-gated sodium channels. However, the mechanism of pyrethroid repellency remains poorly understood and controversial.

Methodology/Principal findings

Here, we show that transfluthrin repels Aedes aegypti in a hand-in-cage assay at nonlethal concentrations as low as 1 ppm. Contrary to a previous report, transfluthrin does not elicit any electroantennogram (EAG) responses, indicating that it does not activate olfactory receptor neurons (ORNs). The 1S-cis isomer of transfluthrin, which does not activate sodium channels, does not elicit repellency. Mutations in the sodium channel gene that reduce the potency of transfluthrin on sodium channels decrease transfluthrin repellency but do not affect repellency by DEET. Furthermore, transfluthrin enhances DEET repellency.

Conclusions/Significance

These results provide a surprising example that sodium channel activation alone is sufficient to potently repel mosquitoes. Our findings of sodium channel activation as the principal mechanism of transfluthrin repellency and potentiation of DEET repellency have broad implications in future development of a new generation of dual-target repellent formulations to more effectively repel a variety of human disease vectors.

Vector-transmitted human diseases, such as dengue fever, represent serious global health burdens. Pyrethroids, including transfluthrin, are widely used as insecticides and repellents due to their low mammalian toxicity and relatively benign environmental impact. Pyrethroids target voltage-gated sodium channels for their insecticidal action. However, the mechanism of pyrethroid repellency remains unclear and controversial. Insect repellency is traditionally thought to be mediated by olfactory receptors. We made two important discoveries in this study, showing that transfluthrin repellency is via activation of sodium channels and transfluthrin enhances DEET repellency. Discovery of sodium channel activation as a major mechanism of pyrethroid repellency has broad significance in insect olfaction study, repellents development, and control of human disease vectors.

Zuccagnia punctata Cav. Essential Oil into Poly(ε-caprolactone) Matrices as a Sustainable and Environmentally Friendly Strategy Biorepellent against Triatoma infestans (Klug) (Hemiptera, Reduviidae)

The main strategies against Triatoma infestans (primary vector responsible for the Chagas disease transmission) are the elimination or reduction of its abundance in homes through the application of insecticides or repellents with residual power, and environmental management through the improvement of housing. The use of plant-derived compounds as a source of therapeutic agents (i.e., essential oils from aromatic plants and their components) is a valuable alternative to conventional insecticides and repellents. Essential oil-based insect repellents are environmentally friendly and provide reliable personal protection against the bites of mosquitoes and other blood-sucking insects. This study investigates, for the first time to our knowledge, the potential repellent activity of Zuccagnia punctata essential oil (ZEO) and poly(ε-caprolactone) matrices loaded with ZEO (ZEOP) prepared by solvent casting. The analysis of its essential oil from aerial parts by GC-FID and GC-MS, MS allowed the identification of 25 constituents representing 99.5% of the composition. The main components of the oil were identified as (-)-5,6-dehydrocamphor (62.4%), alpha-pinene (9.1%), thuja-2, 4 (10)-diene (4.6%) and dihydroeugenol (4.5%). ZEOP matrices were homogeneous and opaque, with thickness of 800 ± 140 µm and encapsulation efficiency values above 98%. ZEO and ZEOP at the lowest dose (0.5% wt./wt., 96 h) showed a repellency of 33 and 73% respectively, while at the highest dose (1% wt./wt., 96 h) exhibited a repellent activity of 40 and 66 %, respectively. On the other hand, until 72 h, ZEO showed a strong repellent activity against T. infestans (88% repellency average; Class V) to both concentrations, compared with positive control N-N diethyl-3-methylbenzamide (DEET). The essential oils from the Andean flora have shown an excellent repellent activity, highlighting the repellent activity of Zuccagnia punctata. The effectiveness of ZEO was extended by its incorporation in polymeric systems and could have a potential home or peridomiciliary use, which might help prevent, or at least reduce, Chagas' disease transmission.

Characterization of a composite with enhanced attraction to savannah tsetse flies from constituents or analogues of tsetse refractory waterbuck (Kobus defassa) body odor

Savannah tsetse flies avoid flying toward tsetse fly-refractory waterbuck (Kobus defassa) mediated by a repellent blend of volatile compounds in their body odor comprised of δ-octalactone, geranyl acetone, phenols (guaiacol and carvacrol), and homologues of carboxylic acids (C₅-C₁₀) and 2-alkanones (C₈-C₁₃). However, although the blends of carboxylic acids and that of 2-alkanones contributed incrementally to the repellency of the waterbuck odor to savannah tsetse flies, some waterbuck constituents (particularly, nonanoic acid and 2-nonanone) showed significant attractive properties. In another study, increasing the ring size of δ-octalactone from six to seven membered ring changed the activity of the resulting molecule (ε-nonalactone) on the savannah tsetse flies from repellency to attraction. In the present study, we first compared the effect of blending ε-nonalactone, nonanoic acid and 2-nonanone in 1:1 binary and 1:1:1 ternary combination on responses of Glossina pallidipes and Glossina morsitans morsitans tsetse flies in a two-choice wind tunnel. The compounds showed clear synergistic effects in the blends, with the ternary blend demonstrating higher attraction than the binary blends and individual compounds. Our follow up laboratory comparisons of tsetse fly responses to ternary combinations with different relative proportions of the three components showed that the blend in 1:3:2 proportion was most attractive relative to fermented cow urine (FCU) to both tsetse species. In our field experiments at Shimba Hills game reserve in Kenya, where G. pallidipes are dominant, the pattern of tsetse catches we obtained with different proportions of the three compounds were similar to those we observed in the laboratory. Interestingly, the three-component blend in 1:3:2 proportion when released at optimized rate of 13.71mg/h was 235% more attractive to G. pallidipes than a combination of POCA (3-n-Propylphenol, 1-Octen-3-ol, 4-Cresol, and Acetone) and fermented cattle urine (FCU). This constitutes a novel finding with potential for downstream deployment in bait technologies for more effective control of G. pallidipes, G. m. morsitans, and perhaps other savannah tsetse fly species, in ‘pull’ and ‘pull-push’ tactics.

In our previous studies with tsetse fly-refractory waterbuck body odor, we found that certain subtle structural changes are associated with shifts in activities of some constituents from repellency to attraction. This led us to discovery of three potent tsetse attractants (ε-nonalactone, nonanoic acid and 2-nonanone). In the present study, we explored possible synergistic effects of blending of these compounds in different proportions to Glossina pallidipes and Glossina m. morsitans in the laboratory, followed by field studies with G. pallidipes. A three-component blend comprised of ε -nonalactone, nonanoic acid and 2-nonanone in 1:3:2 proportion gave 235% higher tsetse fly catches in the field compared with that of POCA and FCU. Thus, dispensing this odor blend in tsetse fly traps or insecticide treated targets is expected to suppress the tsetse flies more efficiently. It will also be interesting to see if the blend is similarly attractive to other savannah tsetse fly species.

QSAR models for insecticidal properties of plant essential oils on the housefly (Musca domestica L.)

The fumigant and topical activities exhibited by 27 plant-derived essentials oils (EOs) on adult M. domestica housefly are predicted through the Quantitative Structure-Activity Relationship (QSAR) theory. These molecular structure based calculations are performed on 253 structurally diverse compounds from the EOs, where the number of constituents in each essential oil mixture varies between 2 to 24. A large number of 86,048 non-conformational mixture descriptors are derived as linear combinations of the molecular descriptors of the EO components. Two strategies are compared for the mixture descriptor formulation, which consider or avoid the use of the chemical composition. The multivariable linear regression QSAR models of the present work are useful for fumigant and topical applications, describing predictive parallelisms for the insecticidal activity of the analysed complex mixtures.

Artemisia abrotanum L. (Southern Wormwood)-History, Current Knowledge on the Chemistry, Biological Activity, Traditional Use and Possible New Pharmaceutical and Cosmetological Applications

Artemisia abrotanum L. (southern wormwood) is a plant species with an important position in the history of European and Asian medicine. It is a species famous as a medicinal plant in Central Asia, Asia Minor, and in South-East and Central Europe. The raw materials obtained from this species are Abrotani herba and Abrotani folium. In the traditional European medicine, they have been used successfully most of all in liver and biliary tract diseases, in parasitic diseases in children and as antipyretic medication. In the official European medicine, this plant species is recommended by the French Pharmacopoeia for use in homeopathy. In many European countries, it is used traditionally in allopathy. The latest studies on the biological activity of extracts from the aboveground parts of the plant and/or the leaves, and/or the essential oil have provided evidence of other possible applications related to their antibacterial, antifungal, antioxidant, anticancer, and antiallergic properties. The latest studies have also focused on the repellent activity of the essential oil of this species and the possibility to use it in the prevention of diseases in which insects are the vectors. The main substances obtained from the plant that are responsible for this activity are: the essential oil, coumarins, phenolic acids, and flavonoids. Some of the latest investigations emphasize the large differences in the composition of the essential oil, determined by the geographical (climatic) origin of the plant. A. abrotanum is recommended by the European Cosmetic Ingredients Database (CosIng) as a source of valuable cosmetic ingredients. Additionally, the leaves of this species possess a well-established position in the food industry. This plant species is also the object of biotechnological studies.

Symbiotic bacteria attenuate Drosophila oviposition repellence to alkaline through acidification

Metazoans harbor a wealth of symbionts that are ever-changing the environment by taking up resources and/or excreting metabolites. One such common environmental modification is a change in pH. Conventional wisdom holds that symbionts facilitate the survival and production of their hosts in the wild, but this notion lacks empirical evidence. Here, we report that symbiotic bacteria in the genus Enterococcus attenuate the oviposition avoidance of alkaline environments in Drosophila. We studied the effects of alkalinity on oviposition preference for the first time, and found that flies are robustly disinclined to oviposit on alkali-containing substrates. This innate repulsion to alkaline environments is explained, in part, by the fact that alkalinity compromises the health and lifespan of both offspring and parent Drosophila. Enterococcus dramatically diminished or even completely reversed the ovipositional avoidance of alkalinity in Drosophila. Mechanistically, Enterococcus generate abundant lactate during fermentation, which neutralizes the residual alkali in an egg-laying substrate. In conclusion, Enterococcus protects Drosophila from alkali stress by acidifying the ovipositional substrate, and ultimately improves the fitness of the Drosophila population. Our results demonstrate that symbionts are profound factors in the Drosophila ovipositional decision, and extend our understanding of the intimate interactions between Drosophila and their symbionts.

A Pichia biosensor for high-throughput analyses of compounds that can influence mosquito behavior

Mosquitoes utilize their sense of smell to locate prey and feed on their blood. Repellents interfere with the biochemical cascades that detect odors. Consequently, repellants are highly effective and resource-efficient alternatives for controlling the spread of mosquito-borne illnesses. Unfortunately, the discovery of repellents is slow, laborious, and error-prone. To this end, we have taken a giant stride toward improving the speed and accuracy of repellant discovery by constructing a prototypical whole-cell biosensor for accurate detection of mosquito behavior-modifying compounds such as repellants. As a proof-of-concept, we genetically engineered Pichia pastoris to express the olfactory receptor co-receptor (Orco) of Anopheles gambiae mosquitoes. This transmembrane protein behaves like a cationic channel upon activation by stimulatory odorants. When the engineered Pichia cells are cultured in calcium-containing Hank's buffer, induction of the medium with a stimulatory odorant results in an influx of calcium ions into the cells, and the stimulatory effect is quantifiable using the calcium-sequestering fluorescent dye, fluo-4-acetoxymethyl ester. Moreover, the stimulatory effect can be titrated by adjusting either the concentration of calcium ions in the medium or the level of induction of the stimulatory odorant. Subsequent exposure of the activated Pichia cells to a repellant molecule inhibits the stimulatory effect and quenches the fluorescent signal, also in a titratable manner. Significantly, the modular architecture of the biosensor allows easy and efficient expansion of its detection range by co-expressing Orco with other olfactory receptors. The high-throughput assay is also compatible with robotic screening infrastructure, and our development represents a paradigm change for the discovery of mosquito repellants.

Insecticidal and acetylcholine esterase inhibition activity of Rhododendron thymifolium essential oil and its main constituent against two stored product insects

In this work, we investigated the bioactivities of the essential oil (EO) extracted from the Rhododendron thymifolium and its principal germacrone against Lasioderma serricorne and Tribolium castaneum. The EO was obtained by steam distillation. Germacrone was obtained by cryogenic crystallization. The bioactivity of EO and germacrone was tested via contact and repellent activity assays. The results showed that EO and germacrone possessed contact and repellent activities against two species of insects. EO exhibited obvious contact activity against the L. serricorn adults, larvae and T. castaneum larvae with LD₅₀ values of 29.15 µg/adult, 42.73 µg/larva, 19.65 µg/larva respectively. Germacrone exhibited excellent contact activity against the L. serricorne adults, larvae and the T. castaneum larvae with LD₅₀ values of 17.18 µg/adult, 20.94 µg/larva, 20.93 µg/larva respectively. And at the highest testing concentrations (78.63 and 15.73 nL/cm²), the repellent activity of EO and germacrone on two target insects was comparable to that of the positive control (DEET) after 30 h exposure. In especially, in the treatment of the 120 h after the repellent activity of EO and germacrone against T.castaneum adults and larvae were still very significant and showed the same level percentage repellency as DEET. Meanwhile, germacrone exhibited inhibition of acetylcholinesterase activity with IC₅₀ values of 3%. The results indicated that the EO of R. thymifolium and germacrone had the potential to be developed as natural insecticides and repellents for the control of T. castaneum and L. serricorne.

Constitutive and Inducible Resistance to Thrips Do Not Correlate With Differences in Trichome Density or Enzymatic-Related Defenses in Chrysanthemum

Western flower thrips (WFT), Frankliniella occidentalis, is a serious insect pest of Chrysanthemum [Chrysanthemum × morifolium Ramat. (Asteraceae)]. Here we have investigated whether genotypic variation in constitutive and inducible resistance to WFT correlates with phenotypic differences in leaf trichome density and the activity of the defense-related enzyme polyphenol oxidase (PPO) in chrysanthemum. Non-glandular and glandular leaf trichome densities significantly varied among ninety-five chrysanthemum cultivars. Additional analyses in a subset of these cultivars, differing in leaf trichome density, revealed significant variation in PPO activities and resistance to WFT as well. Constitutive levels of trichome densities and PPO activity, however, did not correlate with chrysanthemum resistance to WFT. Further tests showed that exogenous application of the phytohormone jasmonic acid (JA) increased non-glandular trichome densities, PPO activity and chrysanthemum resistance to WFT, and that these effects were cultivar dependent. In addition, no tradeoff between constitutive and inducible resistance to WFT was observed. JA-mediated induction of WFT resistance, however, did not correlate with changes in leaf trichome densities nor PPO activity levels. Taken together, our results suggest that chrysanthemum can display both high levels of constitutive and inducible resistance to WFT, and that leaf trichome density and PPO activity may not play a relevant role in chrysanthemum defenses against WFT.

Larvicidal Enzyme Inhibition and Repellent Activity of Red Mangrove Rhizophora mucronata (Lam.) Leaf Extracts and Their Biomolecules Against Three Medically Challenging Arthropod Vectors

The larvicidal potential of crude leaf extracts of Rhizophora mucronata, the red mangrove, using diverse solvent extracts of the plant against the early fourth instar larvae of Anopheles stephensi, Culex quinquefasciatus and Aedes aegypti mosquito vectors was analyzed. The acetone extract of R. mucronata showed the greatest efficacy: for Cx. quinquefasciatus (LC50 = 0.13 mg/mL; LC90 = 2.84 mg/mL), An. stephensi (LC50 = 0.34 mg/mL; LC90 = 6.03 mg/mL), and Ae. aegypti (LC50 = 0.11 mg/mL; LC90 = 1.35 mg/mL). The acetone extract was further fractionated into four fractions and tested for its larvicidal activity. Fraction 3 showed stronger larvicidal activity against all the three mosquito larvae. Chemical characterization of the acetone extract displayed the existence of several identifiable compounds like phytol, 3,7,11,15-tetramethyl-2-hexadecen-1-ol, 1-hexyl-2-nitrocyclohexane, eicosanoic acid etc. Enzyme assay displayed that R. mucronata active F3-fractions exert divergent effects on all three mosquitos' biochemical defensive mechanisms. The plant fractions displayed significant repellent activity against all the three mosquito vectors up to the maximum repellent time of 210 min. Thus, the bioactive molecules in the acetone extract of R. murconata leaves showed significant larvicidal and enzyme inhibitory activity and displayed novel eco-friendly tool for mosquito control.

Plant Natural Products for the Control of Aedes aegypti: The Main Vector of Important Arboviruses

The mosquito species Aedes aegypti is one of the main vectors of arboviruses, including dengue, Zika and chikungunya. Considering the deficiency or absence of vaccines to prevent these diseases, vector control remains an important strategy. The use of plant natural product-based insecticides constitutes an alternative to chemical insecticides as they are degraded more easily and are less harmful to the environment, not to mention their lower toxicity to non-target insects. This review details plant species and their secondary metabolites that have demonstrated insecticidal properties (ovicidal, larvicidal, pupicidal, adulticidal, repellent and ovipositional effects) against the mosquito, together with their mechanisms of action. In particular, essential oils and some of their chemical constituents such as terpenoids and phenylpropanoids offer distinct advantages. Thiophenes, amides and alkaloids also possess high larvicidal and adulticidal activities, adding to the wealth of plant natural products with potential in vector control applications.

Essential Oils Extracted from Different Species of the Lamiaceae Plant Family as Prospective Bioagents against Several Detrimental Pests

On the basis of the side effects of detrimental synthetic chemicals, introducing healthy, available, and effective bioagents for pest management is critical. Due to this circumstance, several studies have been conducted that evaluate the pesticidal potency of plant-derived essential oils. This review presents the pesticidal efficiency of essential oils isolated from different genera of the Lamiaceae family including Agastache Gronovius, Hyptis Jacquin, Lavandula L., Lepechinia Willdenow, Mentha L., Melissa L., Ocimum L., Origanum L., Perilla L., Perovskia Kar., Phlomis L., Rosmarinus L., Salvia L., Satureja L., Teucrium L., Thymus L., Zataria Boissier, and Zhumeria Rech. Along with acute toxicity, the sublethal effects were illustrated such as repellency, antifeedant activity, and adverse effects on the protein, lipid, and carbohydrate contents, and on the esterase and glutathione S-transferase enzymes. Chemical profiles of the introduced essential oils and the pesticidal effects of their main components have also been documented including terpenes (hydrocarbon monoterpene, monoterpenoid, hydrocarbon sesquiterpene, and sesquiterpenoid) and aliphatic phenylpropanoid. Consequently, the essential oils of the Lamiaceae plant family and their main components, especially monoterpenoid ones with several bioeffects and multiple modes of action against different groups of damaging insects and mites, are considered to be safe, available, and efficient alternatives to the harmful synthetic pesticides.

Comparative laboratory efficacy of novel botanical extracts against Tribolium castaneum

BACKGROUND

Citrus sinensis, Allium sativum, Ocimum basilicum, Mentha spicata, Curcuma longa, Carica papaya, Andrographis paniculata, Azadirachta indica, Cymbopogon citratus and Acorus calamus were compared in the form of extracts of chloroform, hexane and aqueous media for their effectiveness in repelling Tribolium castaneum. Filter paper of 9 cm in diameter was cut into halves. Using a micro-pipette, each extract was applied to one half of the filter paper. The volume applied was kept constant at 0.6 mL per 30 cm² . The filter paper was dried and reattached leaving a 0.5 cm gap between, in a Petri-plate. Ten adults of T. castaneum were introduced and the repellency was observed after 30, 60 and 180 min.

RESULTS

The aqueous extract of C. papaya exhibited the highest repellency (82-97%) followed by that of garlic bulbs (aqueous extract) with 86.67% repellency. Further, gunny bags were sprayed separately using bottle sprayers with the two most effective extracts at a constant volume of 42 mL per 575 cm² . These treated gunny bags were compared with malathion-treated gunny bags in the insect management unit. The observations were taken after 2, 8 and 24 h. Papaya leaf extract-treated gunny bags showed relative repellent activity similar to that of malathion-treated gunny bags after 24 h of treatment. Thus, gas chromatography-mass spectrometry analysis of aqueous extract of papaya leaves was performed.

CONCLUSIONS

It can be concluded that extract of papaya leaves containing 2-methoxy-4-vinylphenol (8.47% peak area) can be used as a repellent biopesticide. © 2019 Society of Chemical Industry.

Pyrethroid-Derived Acids and Alcohols: Bioactivity and Synergistic Effects on Mosquito Repellency and Toxicity

Pyrethroids are one of the most commonly used classes of insecticides, and their acid and alcohol components are esterase degradation products, usually considered to be biologically inactive. In this study, it was found that several pyrethroid acids had a spatial repellent activity that was greater than DEET, often more active than the parent pyrethroids, and showed little cross resistance in a pyrethroid-resistant Puerto Rico strain of Aedes aegypti mosquitoes. Further investigation revealed that the acids can synergize not only contact repellent standards but also other pyrethroid components as well as the parent pyrethroids themselves. Synergism by the pyrethroid acids is expressed as both increased spatial repellency and vapor toxicity as well as human bite protection. Electrophysiological studies confirmed that pyrethroid acids (100 μM) had no effect on neuronal discharge in larval Drosophila melanogaster CNS and were detected by electroantennography, and there was little resistance to olfactory sensing of these acids in antennae from Puerto Rico strain mosquitoes carrying kdr mutations. Thus, the data suggest that the pyrethroid acids have a different mode of action than the parent pyrethroids, unrelated to the voltage-sensitive sodium channel. The results highlight the potential of pyrethroid acids to be useful in future repellent formulations.

Toxicity and repellent activity of essential oil from Mentha piperita Linn. leaves and its major monoterpenoids against three stored product insects

The essential oil (EO) from leaves of Mentha piperita was extracted by hydrodistillation. Twenty-one chemical components, accounting for 97.5% of the total oil, were determined by GC-MS and GC-FID. The major chemical components included menthol (41.6%), L-menthone (24.7%), isomenthol (6.3%), and limonene (5.0%). The bioactivity of the obtained EO and its two major components against Tribolium castaneum, Lasioderma serricorne, and Liposcelis bostrychophila adults were evaluated by fumigation, contact, and repellent activity bioassay. The EO showed significant fumigation and contact toxicity against T. castaneum (LC₅₀ = 18.1 mg/L air and LD₅₀ = 2.9 μg/adult, respectively), L. serricorne (LC₅₀ = 68.4 mg/L air and LD₅₀ = 12.6 μg/adult, respectively), and L. bostrychophila (LC₅₀ = 0.6 mg/L air and LD₅₀ = 49.8 μg/adult, respectively) adults. Meanwhile, the repellent effect of the EO on T. castaneum and L. serricorne adults was comparable to that of the positive control at the highest tested concentration. Menthol and L-menthone were two major components in total oil. Among them, L-menthone exhibited significant insecticidal activity on target insects, and menthol showed notable repellent effects. The results indicated that the EO of M. piperita leaves and two tested components have potential to be developed as natural insecticides and repellents for the control of stored product insect pests. Graphical abstract.

Mosquito repellent thermal stability, permeability and air volatility

BACKGROUND

The effectiveness of mosquito repellents, whether applied topically on the skin or released from a wearable device, is determined by the evaporation rate. This is because a repellent has to be present in the form of a vapour in the vicinity of the exposed skin that needs protection. Therefore, gravimetric techniques were used to investigate the direct evaporation of selected liquid repellents, their permeation through polymer films, and their release from a microporous polyethylene matrix.

RESULTS

Evaporation of a repellent into quiescent air is determined by its air permeability. This is a product of the vapour pressure and the diffusion coefficient, i.e. S A = P A sat D A . It was found that repellents could be ranked in terms of decreasing volatility as: ethyl anthranilate > citriodiol > dimethyl phthalate > N,N-diethyl-meta-toluamide (DEET) > decanoic acid > ethyl butylacetylaminopropionate > Icaridin. Experimental S_A values, at 50 °C, ranged from 0.015 ± 0.008 mPa m²  s^-1 for the least volatile repellent (Icaridin) to 0.838 ± 0.077 mPa m²  s^-1 for the most volatile (ethyl anthranilate). The release rate from microporous polyethylene strands, produced by extrusion-compounding into ice water baths followed a similar ranking. These strands featured an integral skin-like membrane that covered the extruded strands and controlled the release of the repellent at a low effective rate.

CONCLUSION

The high thermal and thermo-oxidative stability together with the low volatility of the mosquito repellents ethyl butylacetylaminopropionate and Icaridin make them attractive candidates for long-lasting wearable mosquito-repellent devices. Such anklets/bracelets may have utility for outdoor protection against infective mosquito bites in malaria-endemic regions. © 2019 Society of Chemical Industry.

Design of a Repellent Against Aedes aegypti (Diptera: Culicidae) Using in silico Simulations With AaegOBP1 Protein

Skin irritation has been reported to be the main adverse effect of excessive use of N,N-diethyl-m-toluamide (DEET) and ethyl 3-acetyl(butyl)amino (IR3535) commercial repellents. Therefore, there is an interest in alternatives of natural origin such as essential oils (EOs) and major compounds, which have repellent effects but have no contraindications. The main purpose of the present study was to identify the repellent effect of selected terpenes on Aedes aegypti Linnaeus, 1762 (Diptera: Culicidae) by in silico analysis based on their affinity with the odorant protein AaegOBP1. The protein-metabolite interactions in 20 terpenes were analyzed using the SwissDock tool. Terpenes presenting the highest affinity compared with commercial repellents were selected to evaluate repellent activity at concentrations 0.1, 10, and 25% against Ae. aegypti. Different periods (0-2, 2-15, 15-60 min) were evaluated with DEET as a positive control. The toxicity of terpenes was verified through Osiris and Molinspiration Cheminformatics Software, and cytotoxicity assays in Vero and HepaRG cells were performed using the MTT method. Two formulations were prepared with polyethylene glycol to evaluate skin long-lasting in vivo assay. The results showed four terpenes: geranyl acetate, nerolidol, α-bisabolol, and nerol, with affinity to AaegOBP1 comparable with DEET and IR3535. Geranyl acetate, nerolidol, and their mixtures showed no cytotoxicity and protection percentages close to 100% during the test at concentrations 10 and 25%. Long-lasting assays with geranyl acetate and nerolidol formulate showed 3 h as maximum protection time with 100% protection percentage. These metabolites and their mixtures are candidates to repellent formulations with times and protection percentages similar to DEET.

Efficacy of Active Ingredients From the EPA 25(B) List in Reducing Attraction of Aedes aegypti (Diptera: Culicidae) to Humans

Mosquitoes of the Aedes genus are vectors for dengue, chikungunya, Zika, and yellow fever viruses. Mosquito repellents are an effective way to prevent mosquito bites and reduce the spread of mosquito-borne diseases. In the early 90s, the U.S. Environmental Protection Agency (EPA) published a list of active ingredients that pose minimum risk to human health that can be used as pesticides or repellents without passing the EPA registration process. The present study examined the efficacy of 21 of the active ingredients listed by the EPA 25 (B) exempt list and five commercially available sprays that only contained active ingredients from the EPA 25(B) list in repelling female Aedes aegypti (L.) females. We performed choice bioassays in a controlled laboratory environment, using a Y-tube olfactometer to determine attraction rates of humans to female Ae. aegypti in the presence of one of the 21 active ingredients and five commercially available repellent sprays. We found that cinnamon oil, peppermint oil, spearmint oil, lemongrass oil, and garlic oil reduced mosquito attraction to human odor. Of the five commercial repellent sprays, only one reduced mosquito attraction for up to 30 min in our assay. The EPA 25 (B) list contains active ingredients that under the conditions of our assay repel Ae. aegypti.

Bioactivity and efficacy of essential oils extracted from Artemisia annua against Tribolium casteneum (Herbst. 1797) (Coleoptera: Tenebrionidae): An eco-friendly approach

Tribolium casteneum is a major stored grains pest causing huge loss by secreting toxic quinones' which make the grains unfit for human consumption. Increasing concern about the fast-growing resistance in T. casteneum against fumigants has evoked more intense research worldwide. Therefore, finding an eco-friendly alternative for the management of the pest is of great importance. In this study, the insecticidal activity of the essential oils (EOs) of Artemisia annua is evaluated. Chemical composition of the EOs eluted with methanol and petroleum ether was analysed through Gas chromatography-mass spectrometry (GC-MS). The result has reported a total of 13 & 16 compounds in the methanol and petroleum ether EOs respectively. In contact toxicity studies, adults were found more susceptible to the petroleum ether EOs (LD₅₀ = 0.43 mg adult-¹) than the methanolic EOs (LD₅₀ = 1.87 mg adult-¹). Petroleum ether EOs was also superior in fumigant assays against both the adults (0.81 mg L air^-1) and larvae (0.65 mg L air^-1). Moreover, the same was also recorded as a strong repellent. The bio-molecular studies conducted to gain an insight into the extent of metabolic disturbances inflicted in the treatment sets has shown a significant increase in Lipid peroxidase and decrease (p˂0.01) in protein, Acetylcholinesterase, Glutathione S Transferees, Reduced Glutathione level. This indicates the major signs of oxidative stress in the treatment sets. The Results ascertain the knowledge to develop natural insecticides from Artemisia annua using a potential solvent to be used in the future as an efficient management tool against T. casteneum.