Chemical composition, larvicidal action, and adult repellency of Thymus magnus against Aedes albopictus

Chemical Composition, Larvicidal and Ovicidal Activities, and Enzyme Inhibition Capacity of Thymus serpyllum Essential Oils Against Spodoptera litura (Fabricius)

Due to their effectiveness at low doses and relative safety for non-target species, plant essential oils (EOs) are considered ideal alternatives to conventional pesticides for pest control. In this study, the chemical composition of Thymus serpyllum (T. serpyllum) EO was construed by Gas Chromatography-Mass Spectrometry (GC-MS), and its larvicidal and ovicidal activity against omnivorous pests Spodoptera litura (S. litura) was assessed. The effects of T. serpyllum EO on the activities of antioxidant detoxification enzymes were also measured. GC-MS analysis revealed that the main constituents of T. serpyllum EO were thymol (42.1%), p-cymene (22.4%), and γ-terpinene (18.6%). In the larvicidal toxicity experiment, the T. serpyllum EO demonstrated LC50 values of 0.606 and 0.664 mg/mL against the second- and third-instar larvae of S. litura, respectively, after 48 h exposure. Moreover, an EC50 value of 0.905 mg/mL was measured against S. litura eggs. In S. litura, T. serpyllum EO treatment reduced the enzymatic activity of ESTs and GST and, conversely, increased the enzymatic activity of AChE. Overall, this study demonstrated that T. serpyllum EO has the potential to be implemented as a novel eco-friendly insecticide against S. litura.

Encapsulation of carvacrol and thymol with yeast cell wall and its repellent activity against Amblyomma sculptum and Rhipicephalus sanguineus (Sensu Lato)

The main way to avoid contact with ticks and consequently tick-borne disease is the use of synthetic repellents. The search of new repellent compounds to increase the possibilities of use in strategies controls are necessary. The present study evaluated the repellent activity of two natural terpenes carvacrol and thymol in each one two different formulation (encapsulated and nonencapsulated with yeast cell wall) against the ticks Amblyomma sculptum and Rhipicephalus sanguineus sensu lato nymphs. Nymphs of A. sculptum and R. sanguineus s.l. of a single generation were used. The vertical filter paper repellency assay were performed with different concentration of both terpenes encapsulated and nonencapsulated in yeast cell wall. The repellent concentration 50% (RC50) were calculated to each compound formulation. Both carvacrol and thymol (encapsulated and nonencapsulated), had a repellent activity against A. sculptum and R. sanguineus s.l nymphs. Amblyomma sculptum was more sensitive to nonencapsulated carvacrol (RC50 values: 0.0032 to 0.0082 mg/cm2 after 1 and 15 min) (P < 0.05), while R. sanguineus s.l. was more sensitive to encapsulated carvacrol (RC50 values: 0.00008 to 0.0035 mg/cm2 after 1 and 15 min) (P < 0.05). Among tick species, R. sanguineus s.l. was more sensitive for most compounds than A. sculptum (P < 0.05). Although with distinct repellent activities, carvacrol and thymol encapsulated can be a promising alternative to synthetic repellents against A. sculptum and R. sanguineus s.l.

Behavioral and Electrophysiological Effects of Ajowan (Trachyspermum ammi Sprague) (Apiales: Apiaceae) Essential Oil and Its Constituents on Nymphal and Adult Bean Bugs, Riptortus clavatus (Thunberg) (Hemiptera: Alydidae)

We investigated the repellent effect of 12 Apiaceae plant essential oils on nymphal and adult (male and female) forms of the bean bug, Riptortus clavatus (Thunberg) (Hemiptera: Alydidae), using a four-arm olfactometer. Among the essential oils tested, ajowan (Trachyspermum ammi Sprague) essential oil showed the strongest repellent activity against the nymphal and adult bean bugs. For female adults, the repellent activity was significantly different between an ajowan oil-treated chamber and an untreated chamber down to a concentration of 14.15 μg/cm². We also investigated the repellent activity of individual ajowan essential oil constituents. Of the compounds examined, carvacrol and thymol showed the most potent repellent activity against the nymphal and adult bean bugs. Carvacrol and thymol exhibited 73.08% and 70.0% repellent activity for the bean bug nymph at 0.71 and 2.83 μg/cm², respectively, and 82.6% and 80.7% at 5.66 and 11.32 μg/cm², respectively, for male adults. Carvacrol and thymol exhibited strong repellent activity against female adult bean bugs down to a concentration of 2.83 μg/cm². Ajowan essential oil, thymol and carvacrol elicited a negative electroantennogram (EAG) response from adult bean bugs. This could explain the repellent activity of ajowan essential oil and its constituents. Our results indicate that ajowan essential oil and its constituents carvacrol and thymol can be potential candidates as the 'push' component in a 'push-pull' strategy for bean bug control.

Toxicity and effects of essential oils and their components on Dermanyssus gallinae (Acari: Dermanyssidae)

The acaricidal activity of 30 essential oils against the poultry red mite, Dermanyssus gallinae, female adults and behavioral responses of the mites to these essential oils were investigated. Cinnamon bark oil and clove bud oil showed 100% acaricidal activity after 24 h in the 1.3 μg/m² treatment. In addition, four components in cinnamon bark oil and three components in clove bud oil were identified using gas chromatography-mass spectrometry. Cinnamon bark oil showed the highest LD₅₀ value among all of the components, and eugenol showed 0.97-fold higher relative toxicity (RT) than the other components of clove bud oil. The fumigant effects of both essential oils and their seven components were observed using a vapor phase toxicity bioassay. All the substances showed repellent activity except for cinnamyl acetate, which did not show any repellent response even in the > 10 μg treatment. In the experiment using the T-tube olfactometer with the 10 μg treatment of each substance, D. gallinae female adults responded to all the substances except cinnamyl acetate. However, eugenol and eugenol acetate showed an attractant effect after 240 and 120 min of treatment, respectively. These results suggest that the two studied essential oils and their components may be used as control agents against D. gallinae.

Repellent Effects of Encapsulated Carvacrol on the Rhipicephalus (Boophilus) microplus (Acari: Ixodidae)

Rhipicephalus (Boophilus) microplus (Canestrini) is a problem for livestock production systems, and its control has become challenging due to the selection of tick populations resistant to synthetic chemical acaricides. The use of repellent compounds prevents contact between the arthropod parasite and the host and can, thus, contribute to increases in the efficacy of these acaricides. Carvacrol monoterpenic phenol is a possible alternative method for controlling R. (B.) microplus; however, this compound is highly volatile, and its volatilization can be decreased through microencapsulation, which results in the timed release of the compound. The cell wall of Saccharomyces cerevisiae can be utilized for the protection of volatile molecules. The aim of this study was to evaluate the in vitro repellent effect of yeast cell wall-encapsulated carvacrol on susceptible R. (B.) microplus larvae. Specifically, the vertical filter paper bioassay was employed to analyze the repellent activity of encapsulated carvacrol, nonencapsulated carvacrol, and N,N-diethyl-meta-toluamide at concentrations ranging from 0.75 to 0.001 mg/cm2, and the repellent activities were evaluated. Both carvacrol and encapsulated carvacrol exhibited repellent effects on R. (B.) microplus larvae, and the encapsulated compound showed the highest repellent activities at the lowest concentrations. Carvacrol encapsulated exhibited a low repellent concentration in all times (≤0.05 mg/cm2), whereas the carvacrol nonencapsulated ranged CR50 from 0.13 to 0.27 mg/cm2 at 1- to 6-h posttreatment. The present paper provides the first description of the use of a microencapsulation technique for achieving the highest repellent effect of carvacrol and indicates that this technique might be used to obtain new delivery systems for volatile and hydrophobic compounds.

Synergy in the adulticidal efficacy of essential oils for the improvement of permethrin toxicity against Aedes aegypti L. (Diptera: Culicidae)

BACKGROUND

In a previous screening program for mosquitocides from local edible plants in Thailand, essential oils (EOs) of Cyperus rotundus, Alpinia galanga and Cinnamomum verum, were found to possess promising adulticidal activity against Aedes aegypti. With the aim of reducing usage of conventional insecticides and improving the management of resistant mosquito populations, this study was designed to determine the potential synergism in the adulticidal efficacy of EOs on permethrin toxicity against Ae. aegypti, both pyrethroid-resistant and -susceptible strains.

METHODS

EOs extracted from rhizomes of C. rotundus and A. galanga as well as C. verum barks were evaluated for chemical compositions and adulticidal activity against Muang Chiang Mai-susceptible (MCM-S) and Pang Mai Dang-resistant (PMD-R) strains of Ae. aegypti. Adulticidal bioassays of EO-permethrin mixtures for synergistic activity were also performed on these Ae. aegypti strains.

RESULTS

Chemical characterization by the GC-MS analytical technique demonstrated that 48 compounds were identified from the EOs of C. rotundus, A. galanga and C. verum, representing 80.22%, 86.75% and 97.24%, respectively, of all compositions. Cyperene (14.04%), β-bisabolene (18.27%) and cinnamaldehyde (64.66%) were the main constituents of C. rotundus, A. galanga and C. verum oils, respectively. In adulticidal bioassays, EOs of C. rotundus, A. galanga and C. verum were effective in killing Ae. aegypti, both MCM-S and PMD-R strains, with LD50 values of 10.05 and 9.57 μg/mg female, 7.97 and 7.94 μg/mg female, and 3.30 and 3.22 μg/mg female, respectively. The adulticidal efficacy against MCM-S and PMD-R Ae. aegypti of these EOs was close to that of piperonyl butoxide (PBO, LD50 values = 6.30 and 4.79 μg/mg female, respectively) but less pronounced than that of permethrin (LD50 values = 0.44 and 3.70 ng/mg female, respectively). Nevertheless, combination-based bioassays discovered the accomplished synergism of EOs together with permethrin. Significant synergistic effects with permethrin against both the strains of Ae. aegypti were recorded in the EOs of C. rotundus and A. galanga. Addition of C. rotundus and A. galanga oils decreased the LD50 values of permethrin against MCM-S dramatically from 0.44 to 0.07 and 0.11 ng/mg female, respectively, with synergism ratio (SR) values of 6.28 and 4.00, respectively. Furthermore, EOs of C. rotundus and A. galanga also reduced the LD50 values of permethrin against PMD-R drastically from 3.70 to 0.42 and 0.003 ng/mg female, respectively, with SR values of 8.81 and 1233.33, respectively.

CONCLUSIONS

The synergy of enhanced adulticidal toxicity recorded from EO-permethrin combinations against both strains of Ae. aegypti presents a promising role of EOs as a synergist for improving mosquitocidal efficacy, particularly in situations where conventional compounds are ineffective or inappropriate.

Zingiber cernuum (Zingiberaceae) essential oil as effective larvicide and oviposition deterrent on six mosquito vectors, with little non-target toxicity on four aquatic mosquito predators

Mosquitoes are responsible for the transmission of many pathogens and parasites, which cause serious diseases in humans and animals. Currently, botanical products have been suggested as alternative tools in the fight against arthropod vectors. In this study, the essential oil (EO) extracted from Zingiber cernuum was tested as larvicide and oviposition deterrent on six mosquito species of public health relevance, including malaria and Zika virus vectors. The EO showed high toxicity on third instar larvae of Anopheles stephensi (LC₅₀ = 41.34 μg/ml), Aedes aegypti (LC₅₀ = 44.88 μg/ml), Culex quinquefasciatus (LC₅₀ = 48.44 μg/ml), Anopheles subpictus (LC₅₀ = 51.42 μg/ml), Aedes albopictus (LC₅₀ = 55.84 μg/ml), and Culex tritaeniorhynchus (LC₅₀ = 60.20 μg/ml). In addition, low doses of Z. cernuum EO reduced oviposition rates in six mosquito species. The acute toxicity of Z. cernuum EO on four mosquito predators was scarce; LC₅₀ ranged from 3119 to 11,233 μg/ml. Overall, our results revealed that the Z. cernuum EO can be considered for the development of effective and environmental-friendly mosquito larvicides and oviposition deterrents.

Acaricidal and repellent effects of Cnidium officinale-derived material against Dermanyssus gallinae (Acari: Dermanyssidae)

The acaricidal activity of a methanolic extract and fractions from the rhizome of Cnidium officinale against Dermanyssus gallinae adults was investigated. The C. officinale methanolic extract exhibited 100% acaricidal activity after 48 h of treatment at a dose of 4000 ppm. The acaricidal constituents of the plant were sequentially partitioned with several solvents and then purified using silica gel column chromatography and high-performance liquid chromatography. Gas chromatography-mass spectrometry and nuclear magnetic resonance spectroscopy revealed (Z)-ligustilide as a constituent of C. officinale. Acaricidal activity was examined in three experimental tests (spray, fumigation and contact), with the spraying method being the most effective. The methanolic extract of C. officinale showed both contact and fumigant activities, though only fumigant activity was observed with (Z)-ligustilide. The fumigant effects of the methanolic extract and (Z)-ligustilide caused 86.5 and 62.6% mortality, respectively, of D. gallinae adults at 48 h. Among (Z)-ligustilide, acaricides (bifenthrin, cypermethrin and spinosad) and butylidenephthalide, bifenthrin displayed the highest acaricidal activity, and the activity of butylidenephthalide was 2.3-fold higher than that of (Z)-ligustilide. These results suggest that C. officinale-derived material can be used for the development of a control agent for D. gallinae.

Fumigant Activity of 6 Selected Essential Oil Compounds and Combined Effect of Methyl Salicylate And Trans-Cinnamaldehyde Against Culex pipiens pallens

We studied the knockdown activity and lethal toxicity of 6 essential oil compounds-methyl salicylate, linalool, 2-phenethyl alcohol, eugenol, β-citronellol, and trans-cinnamaldehyde-as fumigants against adult female Culex pipiens pallens in the laboratory. Of the 6 products tested, trans-cinnamaldehyde was the most toxic (LC50  =  0.26 µl/l air, 24 h) with a slow knockdown time (KT95  =  176.5 min at 0.5 µl/l air). Methyl salicylate displayed a lower toxicity (LC50  =  1.17 µl/l air, 24 h) but the fastest knockdown activity (KT95  =  16.8 min) at the sublethal concentration 0.5 µl/l air. Furthermore, the binary mixture of methyl salicylate and trans-cinnamaldehyde exhibited a combined effect of fast knockdown activity and high toxicity against Cx. p. pallens adults, showing potential for development as natural fumigants for mosquito control.

Comparative investigation of Umbellularia californica and Laurus nobilis leaf essential oils and identification of constituents active against Aedes aegypti

Umbellularia californica (California bay laurel) and Laurus nobilis (Mediterranean bay laurel) leaves may be mistaken or used as a substitute on the market due to their morphological similarity. In this study, a comparison of anatomical and chemical features and biological activity of both plants is presented. L. nobilis essential oil biting deterrent and larvicidal activity were negligible. On the other hand, U. californica leaf oil showed biting deterrent activity against Aedes aegypti . The identified active repellents was thymol, along with (-)-umbellulone, 1,8-cineole, and (-)-α-terpineol. U. californica essential oil also demonstrated good larvicidal activity against 1-day-old Ae. aegypti larvae with a LD50 value of 52.6 ppm. Thymol (LD50 = 17.6 ppm), p-cymene, (-)-umbellulone, and methyleugenol were the primary larvicidal in this oil. Umbellulone was found as the principal compound (37%) of U. californica essential oil, but was not present in L. nobilis essential oil. Umbellulone mosquito activity is here reported for the first time.