Protection against mosquito vectors Aedes aegypti, Anopheles stephensi and Culex quinquefasciatus using a novel insect repellent, ethyl anthranilate

Repellent effect of two anthranilates against the tropical bed bug Cimex hemipterus (Hemiptera: Cimicidae) demonstrated in laboratory assays

BACKGROUND

The bites and blood sucking of bed bugs (Cimex spp.) (Hemiptera: Cimicidae) pose a serious threat to human physical and mental health. Application of an effective repellent can prevent or reduce bed bug bites. Previous studies on repellent screening mainly focused on Cimex lectularius L. In this study, we investigated the repellent effect of two safe food additives, ethyl anthranilate (EA) and butyl anthranilate (BA), against Cimex hemipterus (F.), and also explored the role of antennae and mouthparts on C. hemipterus perception of repellents.

RESULTS

Both EA and BA had a strong repellent effect against tropical bed bugs and their repellency was similar or lower than that of N,N-diethyl-3-methyl benzoyl amide, depending on whether or not a CO2 source was present. EA had higher repellency than BA and exhibited repellency to C. hemipterus for 3 days when a CO2 source was present. C. hemipterus avoided resting on 20% EA- and BA-treated harborages. Applying 20% EA and BA on rabbit skin significantly reduced the blood intake of C. hemipterus within 2 h. C. hemipterus could perceive EA and BA after their antennae or mouthparts or both antennae and mouthparts were removed.

CONCLUSION

Both EA and BA had strong repellency against C. hemipterus, with EA being more repellent. Ablation of antennae and mouthparts did not affect the perception of EA and BA by C. hemipterus. © 2023 Society of Chemical Industry.

Synthesis of a Novel Cationic Dye to Impart Mosquito-Repellent and UV Protection to an Acrylic Fabric

The growing demand for innovative routes to develop functional textiles initiated the necessity of new efficient functional molecules. Dyes can provide durable functional protection to textiles due to their ability to generate strong dye-fiber interaction. New dyes to improve a dyed substrate's quality and aesthetic appearance are in huge demand. This research aims to prepare a mosquito-repellent and UV-protective acrylic fabric using a novel cationic (basic) dye. The cationic dye was synthesized and thoroughly characterized with the help of FTIR, ¹H NMR, ¹³C NMR, and CHN analysis. The dye was further used for the dyeing of the acrylic fabric by using an infrared dyeing machine. To analyze the suitability of dyed fabrics for daily use, washing, rubbing, and light fastness of dyed fabrics were determined. The amount of dye (%) taken up by the acrylic fabric (exhaustion %) was determined, and more than 72% of exhaustion was obtained. The fixation (%) of the dye on acrylic fabrics was also quantified, and more than 80% fixation was obtained. The coloration properties of the dyed fabrics (L*, a*, b*, and K/S) were examined. The dyed fabrics showed a K/S of more than 3. The mosquito-repellent action provided by the dyed fabrics was also analyzed, and 100% repellency was obtained. The dyed fabrics provided an excellent UV-protective property. The multifunctional properties of dyed fabrics were retained significantly even after laundering treatments. The dyed fabrics were characterized using X-ray diffraction and thermogravimetric analysis. A reduction in crystalline peak intensity after dyeing was obtained. The dyed and undyed fabrics were also tested for their tensile strength.

Natural Repellents as a Method of Preventing Ant Damage to Microirrigation Systems

Simple Summary

Ants play an essential role in most agroecosystems. However, these insects can occasionally be detrimental to agricultural microirrigation equipment by chewing on tubing parts and causing uneven water distribution along the crops. One of the alternatives traditionally proposed to avoid this damage is the incorporation of substances into the tube material that deter or reduce chewing activity. However, the few attempts made prior to this research were unsuccessful due to the unsuitability of the selected substances and the methods used to integrate them into the tubing. In this study, we assessed the protective efficacy of this method in pipes used for subsurface drip irrigation (SDI). Unlike traditional attempts, we selected nontoxic compounds previously proven to be repellent against ants and integrated them into drip tubing through complex processes such as plastic compounding, injection and extrusion. The use of this type of tubing in a crop where significant ant damage is often reported revealed minimum damage when compared to control tubing containing no repellent additives. This suggests the efficiency of this method in providing protection against ants, but further studies are recommended prior to the commercialization of the designed system.

Abstract

Ants are important because they damage agricultural equipment, including microirrigation systems. The aim of this research was to assess the efficiency of the incorporation of repellents in drip irrigation tubing as a method of protection against ant damage. Unlike previous studies, we tested a series of nontoxic compounds that are repellent to ants. First, we assessed their repellent effects on a local ant species via olfactometer trials. Then, the candidates showing the best results (cinnamon essential oil, p-anisaldehyde and ethyl anthranilate) were incorporated via compounding, injection and extrusion to polyethylene tubing to test their efficiency in the field. Field tests showed high damage levels in the control tubing containing no repellents, presumably caused by up to six different ant species (Cardiocondyla batesii, Plagiolepis pygmaea, P. schmitzii, Solenopsis sp., Tapinoma nigerrimum and Tetramorium semilaeve). In contrast, the pipes containing the three selected compounds remained almost intact, with the treatment including ethyl anthranilate showing no damage at all. These results suggest the strong repellent potential of the selected compounds, even when integrated into plastic, as well as the apparent success of the proposed methodology against the damage caused by ants. The diversity of damage-causing agents that exist in or above the soil strongly encourages further studies to determine the overall efficiency of repellents in protecting irrigation pipes.

Mosquito Olfactory Response Ensemble enables pattern discovery by curating a behavioral and electrophysiological response database

Many experimental studies have examined behavioral and electrophysiological responses of mosquitoes to odors. However, the differences across studies in data collection, processing, and reporting make it difficult to perform large-scale analyses combining data from multiple studies. Here we extract and standardize data for 12 mosquito species, along with Drosophila melanogaster for comparison, from over 170 studies and curate the Mosquito Olfactory Response Ensemble (MORE), publicly available at https://neuralsystems.github.io/MORE. We demonstrate the ability of MORE in generating biological insights by finding patterns across studies. Our analyses reveal that ORs are tuned to specific ranges of several physicochemical properties of odorants; the empty-neuron recording technique for measuring OR responses is more sensitive than the Xenopus oocyte technique; there are systematic differences in the behavioral preferences reported by different types of assays; and odorants tend to become less attractive or more aversive at higher concentrations.

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MORE is a database of behavioral and electrophysiological responses to odors

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MORE includes data from 170 studies covering 12 species of mosquitoes along with flies

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MORE shows differences in odor preferences measured with different assays

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Empty-neuron technique measures responses more sensitively than the oocyte technique

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.

Mosquito-repellent controlled-release formulations for fighting infectious diseases

Malaria is a principal cause of illness and death in countries where the disease is endemic. Personal protection against mosquitoes using repellents could be a useful method that can reduce and/or prevent transmission of mosquito-borne diseases. The available repellent products, such as creams, roll-ons, and sprays for personal protection against mosquitoes, lack adequate long-term efficacy. In most cases, they need to be re-applied or replaced frequently. The encapsulation and release of the repellents from several matrices has risen as an alternative process for the development of invention of repellent based systems. The present work reviews various studies about the development and use of repellent controlled-release formulations such as polymer microcapsules, polymer microporous formulations, polymer micelles, nanoemulsions, solid-lipid nanoparticles, liposomes and cyclodextrins as new tools for mosquito-borne malaria control in the outdoor environment. Furthermore, investigation on the mathematical modelling used for the release rate of repellents is discussed in depth by exploring the Higuchi, Korsmeyer-Peppas, Weibull models, as well as the recently developed Mapossa model. Therefore, the studies searched suggest that the final repellents based-product should not only be effective against mosquito vectors of malaria parasites, but also reduce the biting frequency of other mosquitoes transmitting diseases, such as dengue fever, chikungunya, yellow fever and Zika virus. In this way, they will contribute to the improvement in overall public health and social well-being.

Essential oil based controlled-release non-toxic evaporating tablet provides effective repellency against Musca domestica

Housefly, Musca (M) domestica L. (Diptera: Muscidae) is a pervasive insect that transmits a variety of pathogens to humans and livestock. Although numerous synthetic pesticides are available to combat houseflies, their ecological and toxicological concerns have led to the exploration of natural products as safer alternatives. The present work was designed to develop an essential oil based controlled-release evaporating tablet (EO-CRT) and investigate its repellency against M. domestica. This study assesses the toxicological impacts of the EO-CRT following its sub-chronic inhalation exposure. Briefly, repellent activity of fourteen essential oils viz. lemon grass, bergamot, mentha, basil, camphor, lavender, clove, patchouli, rosemary, cinnamon, eucalyptus, citronella, jasmine and wild turmeric against M. domestica were screened using the 'Y'-tube olfactometer. The synergistic activity of the best four oils, under preliminary screening, were further evaluated by double and triple blending. The best combination of three oils were finalized for optimization with 17-run, 3-factor, 3-level Box-Behnken design. This was then employed to construct polynomial models and predict the best optimized formulation EO-CRT. EO-CRT was characterized by Differential Scanning Calorimetry (DSC) and Gas Chromatography-Mass Spectroscopy (GC-MS). The efficacy of the EO-CRT against M. domestica was assessed by attraction and repellent assay. Chest X-ray, histopathology and scanning electron microscopy of the exposed lung was performed to study EO-CRT's sub-chronic toxicity on Wistar rats. The EO-CRT showed slow release up to a period of 10 days at room temperature, exhibited 100% repellency (%Error=1.237) against M. domestica and was found to possess all the characteristics of an ideal formulation. Sub-chronic toxicity study further revealed the non-toxic nature of the EO-CRT. Thus, our study provides an assurance that the formulated EO-CRT could be effective not only in repelling the nuisance pest, M. domestica, in human dwellings, but also in minimizing the mechanical transmission of pathogens by it.

Design, development and assessment of an essential oil based slow release vaporizer against mosquitoes

Mosquitoes (Diptera; Culicidae) are a biting nuisance and are of economic and health importance, especially for people living in tropical countries like India. Given the environmental concerns and health hazards of synthetic insecticides, development of natural products for the control of mosquito and mosquito-borne diseases are needed. In view of this, an essential oil based novel liquid vaporizer formulation with citronella and eucalyptus oils has been developed using a computer aided Artificial Neural Network and Particle Swarm Optimization (ANN-PSO) algorithm approach, aiming to predict the best optimized formulation (OF). Following the development, OF was characterized by Fourier Transform-Infra Red (FT-IR) spectroscopy and gas chromatography-mass spectroscopy (GC-MS). The efficacy of the OF was assessed against two major mosquito vectors viz. Anopheles stephensi and Aedes albopictus using a Peet-Grady chamber. Finally, toxicological impacts of the OF following its inhalation were investigated as per the Organization for Economic Co-operation and Development (OECD) guidelines. The results revealed all the ideal characteristics of the OF which were found to provide a slow release of up to 450 h at room temperature. Most importantly, the OF, exhibited 50% mosquito knock down (KT₅₀) within 11.49±1.34 and 14.15±2.15 min against An. stephensi and Ae. albopictus respectively. Toxicity assessment showed a non toxic nature of the OF following inhalation. Thus the present development would be beneficial for controlling both An. stephensi and Ae. albopictus without any associated health hazards.

Toxicity and repellency of two anthranilates against Aedes albopictus Skuse (Diptera: Culicidae)

The ability of Aedes albopictus Skuse to transmit several pathogens to humans makes it a very important mosquito with public health significance. Ecofriendly products as alternatives to synthetic chemicals for the control of mosquito vectors are needed. Therefore, the larvicidal and repellent effects of two nontoxic chemicals, butyl anthranilate (BA) and ethyl anthranilate (EA), at different concentrations were compared in A. albopictus. The repellency persistence of BA and three commercial mosquito repellent products (Liushen repellent spray, DKB Korean, Raid repellent spray) against A. albopictus was compared. The results showed that 0.1% concentrations of BA and EA solutions were highly toxic to A. albopictus larvae, and the mortality rate was >90% after 4 h of treatment. We found that BA was more repellent than EA, and at 0.1% BA and 1% EA, and the repellency rates were 53.62% and 38.47%, respectively. Overall, 5% BA presented a significantly longer repellency time than the three commercial repellent products against female A. albopictus. These results indicate that BA has significant larvicidal and repellent effects and can be exploited further for the development of ecofriendly alternatives to existing toxic chemicals currently used for mosquito control.

Visual test for the presence of the illegal additive ethyl anthranilate by using a photonic crystal test strip

A test strip has been developed for the rapid detection of the illegal additive ethyl anthranilate (EA) in wine. The detection scheme is based on a combination of photonic crystal based detection and molecular imprinting based recognition. The resulting molecularly imprinted photonic crystal (MIPC) undergoes a gradual color change from green to yellow to red upon binding of EA. A semi-quantitative colorimetric card can be used to estimate the content of EA, either visually or by making use of an optical fiber spectrometer. A linear relationship was found between the Bragg diffraction peak shift and the concentration of EA in the range from 0.1 mM to 10 mM. The detection limit is 10 μM. The test has been successfully used to screening for the presence of EA in grape wine. The test strip is selective, and can be re-used after re-activation. Graphical abstract Schematic representation of the fabrication and application of the molecularly imprinted photonic crystal (MIPC) based test trip. The resulting MIPC undergoes a gradual color change from green to yellow to red upon binding of the illegal wine additive ethyl anthranilate (EA).

Development of a validated RP-HPLC/DAD method for the quantitative determination of methyl jasmonate in an insect repellent semi-solid formulation

A simple and efficient reversed-phase high-performance liquid chromatographic (RP-HPLC) method has been developed for the first time for the estimation of a mosquito repellent, methyl jasmonate in a cream formulation, and validated as per the International Conference on Harmonization guidelines. Acetonitrile and water (75:25 v/v) were used as the mobile phase and the flow-rate of the mobile phase was kept constant at 1.0 mL/min. The analysis was performed isocratically on a C₁₈ analytical column (250 × 4.4 mm, 5 μm) using a Diode Array Detector for the detection of methyl jasmonate at 214 nm. The presence of excipients did not interfere with the quantification of methyl jasmonate. The calibration curve was linear in the concentration range of 25–300 μg/mL. The relative standard deviations for intra-day and inter-day precision, and repeatability were less than 2%. The recovery ranged from 88.5% to 90.7% with relative standard deviations not higher than 2%. The limit of detection and quantification were 9.4 μg/mL and 28.5 μg/mL, respectively. System suitability parameters were within the accepted range. The proposed method was also robust. Thus, the present report puts forward a novel analytical method for the estimation of an emerging mosquito repellent, methyl jasmonate by using the RP-HPLC technique.

Evidence Based Efficacy of Selected Herbal Extracts Against <i>Culex quinquefasciatus</i> (Say) Larvae

BACKGROUND AND OBJECTIVE

Chemical insecticides have some limitations in vectors control such as the emergence of resistance in vector mosquitoes to conventional synthetic insecticides. It aimed to evaluate the larvicidal efficacy and phytochemical potential of Azadirachta indica, Cymbopogon citratus and Allium sativum L. against ulex quinquefasciatus fourth instar larvae.

MATERIAL AND METHODS

The plants were screened and evaluated for their phytochemical composition and larvicidal effects on . quinquefasciatus larvae.

RESULTS

The bioassay results showed that the effects were dependent on time and concentration of the extract used. Results showed the least lethal dose value for ethanolic extract of . citrates (72 h exposure) and the highest value for aqueous extract of A. indica (24 h exposure). Chi-square values were significant at p<0.05. Phytochemical analysis showed phytochemicals such as alkaloids, flavonoids, cardiac glycosides and resins in all the three plants. However, tannins were absent in A. indica and A. sativum, while balsam was only present in A. indica. Saponins, balsam and phenols were not found in A. sativum. Phenols were also absent in . citratus. Terpenes, steroids and resins were absent A. indica.

CONCLUSION

Findings of this study revealed that these herbal extracts constitute an effective eco-friendly approach for the control of . quinquefasciatus larvae.

Soluble expression of recombinant midgut zymogen (native propeptide) proteases from the Aedes aegypti Mosquito Utilizing E. coli as a host

Background

Studying proteins and enzymes involved in important biological processes in the Aedes aegypti mosquito is limited by the quantity that can be directly isolated from the mosquito. Adding to this difficulty, digestive enzymes (midgut proteases) involved in metabolizing blood meal proteins require a more oxidizing environment to allow proper folding of disulfide bonds. Therefore, recombinant techniques to express foreign proteins in Escherichia coli prove to be effective in producing milligram quantities of the expressed product. However, with the most commonly used strains having a reducing cytoplasm, soluble expression of recombinant proteases is hampered. Fortunately, new E. coli strains with a more oxidizing cytoplasm are now available to ensure proper folding of disulfide bonds.

Results

Utilizing an E. coli strain with a more oxidizing cytoplasm (SHuffle® T7, New England Biolabs) and changes in bacterial growth temperature has resulted in the soluble expression of the four most abundantly expressed Ae. aegypti midgut proteases (AaET, AaSPVI, AaSPVII, and AaLT). A previous attempt of solubly expressing the full-length zymogen forms of these proteases with the leader (signal) sequence and a modified pseudo propeptide with a heterologous enterokinase cleavage site led to insoluble recombinant protein expression. In combination with the more oxidizing cytoplasm, and changes in growth temperature, helped improve the solubility of the zymogen (no leader) native propeptide proteases in E. coli. Furthermore, the approach led to autocatalytic activation of the proteases during bacterial expression and observable BApNA activity. Different time-points after bacterial growth induction were tested to determine the time at which the inactive (zymogen) species is observed to transition to the active form. This helped with the purification and isolation of only the inactive zymogen forms using Nickel affinity.

Conclusions

The difficulty in solubly expressing recombinant proteases in E. coli is caused by the native reducing cytoplasm. However, with bacterial strains with a more oxidizing cytoplasm, recombinant soluble expression can be achieved, but only in concert with changes in bacterial growth temperature. The method described herein should provide a facile starting point to recombinantly expressing Ae. aegypti mosquito proteases or proteins dependent on disulfide bonds utilizing E. coli as a host.

Electronic supplementary material

The online version of this article (10.1186/s12858-018-0101-0) contains supplementary material, which is available to authorized users.

Exploration of toxicological impacts following acute and sub-chronic exposure to ethyl anthranilate-loaded mosquito repellent patch

In the recent years, growing concern about the potential toxicity of synthetic repellents has led to the development of environmentally safe non-toxic insect control methods. Present investigation explores the toxicological impacts of ethyl anthranilate-loaded mosquito repellent patch (EAMRP) on respiratory system following acute and sub-chronic inhalation exposure in Wistar rats. Lungs parameters such as enhanced pause, tidal volume, respiration rate, inspiration time, and expiration time were determined using whole body plethysmograph. X-ray, scanning electron microscopy and histology were utilized to study the morphology and microscopical architecture of lungs. Hematological and serum biochemical markers were estimated. Cytokines such as IL-1β, IL-2, and IL-12 were also estimated in bronchoalveolar lavage fluid using ELISA kits. Finally, acute oral and dermal toxicity studies were carried out to study the accidental or intentional poisoning due to the ingestion and skin contact of EAMRP, respectively. The findings demonstrate that inhalation exposure to EAMRP did not pose any significant dose related toxicity in above mentioned experiments. Further, no appreciable toxicity was observed in both acute oral and dermal exposure. Thus, these results revealed the non toxic nature of EAMRP in preclinical studies. Hence, EAMRP can be used successfully as an alternative to existing synthetic repellents without any potential health hazards.

Methyl N-methylanthranilate: major compound in the defensive secretion of Typhloiulus orpheus (Diplopoda, Julida)

The defensive secretion of the julid diplopod Typhloiulus orpheus contains methyl N-methylanthranilate (MNMA), an ester of N-methylanthranilic acid that comprises more than 99% of secretion of this species. MNMA is accompanied by small amounts of methyl anthranilate and two benzoquinones (2-methyl-1,4-benzoquinone and 2-ethyl-1,4-benzoquinone, respectively). MNMA is a known intermediate in the biosynthesis of both benzoquinones (as present in defensive secretions of juliformians) and glomerin-like quinazolines (chemical defense in Glomerida). The compound may have evolved independently in the pathway to glomeridan chemistry, or may even represent a pivotal branching point in the pathway to different chemical classes of diplopod defensive chemistry.