Ultra low concentration deltamethrin loaded patch development and evaluation of its repellency against dengue vector Aedes (S) albopictus

BACKGROUND

Mosquito repellents and emanators confer protection against mosquito bites through spatial action of emanated vapours which are released into the adjoining environment. Synthetic insecticides released into the environment in ultra low volume vapour phase deter the mosquitoes from biting humans in a protected space.

METHODS

Formulation patches were prepared using the solvent evaporation method over a backing membrane and using Dibutylphthalate (DBT) as a plasticizer. The effect of formulation variables on the deltamethrin release from the patch matrices were studied under accelerated conditions, whereas, HPLC was used for quantitative estimation of deltamethrin. The prepared patch formulations were subjected to physicochemical studies, such as, deltamethrin content, thickness, weight variation, percent moisture content, moisture uptake, surface area and surface pH determination. Deltamethrin-polymer interaction and compatibility was ascertained using DSC and FT-IR, while surface morphology and deltamethrin distribution in the patch were studied using SEM technique. Repellent activity of the patch formulations was evaluated against Ae. albopictus mosquitoes.

RESULTS

Blends of polymeric combinations of polyvinylpyrrolidone (PVP) and ethyl-cellulose (EC) with admixture of deltamethrin provided prolonged repellent activity against Ae. albopictus mosquitoes. Physicochemical characterisation indicated the suitability of deltamethrin patch formulation with the polymeric combinations of PVP and EC. Patches were very effective against laboratory reared Ae. albopictus mosquitoes. No significant difference was observed between the performance of test patches and commercially available repellent cream Mosqshield®.

CONCLUSION

Deltamethrin loaded patches provided effective repellency against Ae. albopictus mosquitoes. The study emphasised that deltamethrin released to the environment in low concentration could be an excellent spatial repellent against hematophagous mosquitoes.

Promising Aedes aegypti repellent chemotypes identified through integrated QSAR, virtual screening, synthesis, and bioassay

Molecular field topology analysis, scaffold hopping, and molecular docking were used as complementary computational tools for the design of repellents for Aedes aegypti, the insect vector for yellow fever, chikungunya, and dengue fever. A large number of analogues were evaluated by virtual screening with Glide molecular docking software. This produced several dozen hits that were either synthesized or procured from commercial sources. Analysis of these compounds by a repellent bioassay resulted in a few highly active chemicals (in terms of minimum effective dosage) as viable candidates for further hit-to-lead and lead optimization effort.

Identification of repellent and insecticidal constituents of the essential oil of Artemisia rupestris L. aerial parts against Liposcelis bostrychophila Badonnel

The aim of this research was to determine the chemical composition and insecticidal and repellent activity of the essential oil of Artemisia rupestris L. aerial parts against the booklice Liposcelis bostrychophila Badonnel and isolation of insecticidal and repellent constituents from the essential oil. The essential oil of A. rupestris was obtained by hydrodistillation and analyzed by GC-MS. A total of 30 components of the essential oil of A. rupestris was identified and the principal compounds in the essential oil were α-terpinyl acetate (37.18%), spathulenol (10.65%), α-terpineol (10.09%), and linalool (7.56%), followed by 4-terpineol (3.92%) and patchoulol (3.05%). Based on bioactivity-guided fractionation, the four active constituents were isolated from the essential oil and identified as α-terpineol, α-terpinyl acetate, 4-terpineol and linalool. The essential oil of A. rupestris exhibited contact toxicity against L. bostrychophila with LD₅₀ value of 414.48 µg/cm². α-Terpinyl acetate (LD₅₀ = 92.59 µg/cm²) exhibited stronger contact toxicity against booklice than α-terpineol (LD₅₀ = 140.30 µg/cm²), 4-terpineol (LD₅₀ = 211.35 µg/cm²), and linalool (LD₅₀ = 393.16 µg/cm²). The essential oil of A. rupestris (LC₅₀ = 6.67 mg/L air) also possessed fumigant toxicity against L. bostrychophila while the four constituents, 4-terpineol, α-terpineol, α-terpinyl acetate and linalool had LC₅₀ values of 0.34, 1.12, 1.26 and 1.96 mg/L air, respectively. α-Terpinol and α-terpinyl acetate showed strong repellency against L. bostrychophila, while linalool and 4-terpinol exhibited weak repellency. The results indicate that the essential oil of A. rupestris aerial parts and its constituent compounds have potential for development into natural insecticides or fumigants as well as repellents for control of insects in stored grains.

A host-plant-derived volatile blend to attract the apple blossom weevil Anthonomus pomorum - the essential volatiles include a repellent constituent

BACKGROUND

Plant volatiles are promising cues for trapping pest insects. This study started with a recently identified complex blend released by prebloom apple trees and aimed to reduce the number of compounds in the blend while maintaining the attraction of the target pest, the apple blossom weevil Anthonomus pomorum. An evaluation was made to determine whether attraction to plant volatiles is a general feature in this species.

RESULTS

Laboratory-based bioassays with field-collected weevils demonstrated repellency by volatiles from the non-host walnut, indicating that preference for plant odours is not a general feature in this species. By a subtractive bioassay approach, the original number of compounds in the apple-plant-released blend was stepwise reduced from 12 to 6 while maintaining weevil attraction. This resulting blend was as attractive as the full blend and as a blossom-bud-carrying apple twig. It was found to be composed of two synergistically interacting constituents, of which the first containing benzenoids was behaviourally inactive, and the second comprising the remaining compounds was even repellent.

CONCLUSIONS

This study enhances knowledge of the interaction of behaviourally effective constituents in complex odour blends and contributes to the development of an efficient monitoring system involving plant volatiles for the apple blossom weevil.

Behavioral and toxicological responses of Rhodnius prolixus and Triatoma infestans (Hemiptera: Reduviidae) to 10 monoterpene alcohols

The effect on locomotor activity, the repellency, and the knock-down produced by 10 monoterpene alcohols were evaluated on first-instar nymphs of Rhodnius prolixus and Triatoma infestans, vectors of Chagas disease. A video tracking technique was used to evaluate locomotor activity and repellency by exposure to papers impregnated with monoterpenes. Eugenol on R. prolixus and (S)-cis-verbenol on T. infestans did not modify the locomotor activity. The remaining monoterpenes produced hyperactivity on both species, although the concentration required was at least a 1,000 times higher than that of deltamethrin (positive control). Carvacrol, eugenol, and geraniol resulted as repellent as N,N-diethyl-m-toluamide (positive control) for both species. A similar result was observed for almost every monoterpene on T. infestans. Knock-down effect was evaluated by exposing the nymphs in closed recipients. The order of increasing toxicity on R. prolixus was (KT50 values in min): geraniol (213.7) < alpha-terpineol (164.5) < linalool (124.2) < carvacrol (111.6) < eugenol (89.8) < thymol (78.9), and on T. infestans: alpha-terpineol (289.8) < eugenol (221.3) < carvacrol (164.2) < linalool (154.9) < thymol (96.7). All monoterpenes were less toxic than the positive control, dichlorvos (3.6 min for R. prolixus and 3.9 min for T. infestans). After 7 h of exposure, (-)-carveol, citronellol, and menthol (on both species) and geraniol (on T. infestans) produced < 50% of knock-down. After these results, it is worthwhile to explore more deeply the potential of these compounds as tools for controlling Chagas disease vectors.

Can topical insect repellents reduce malaria? A cluster-randomised controlled trial of the insect repellent N,N-diethyl-m-toluamide (DEET) in Lao PDR

Background

Mosquito vectors of malaria in Southeast Asia readily feed outdoors making malaria control through indoor insecticides such as long-lasting insecticidal nets (LLINs) and indoor residual spraying more difficult. Topical insect repellents may be able to protect users from outdoor biting, thereby providing additional protection above the current best practice of LLINs.

Methods and Findings

A double blind, household randomised, placebo-controlled trial of insect repellent to reduce malaria was carried out in southern Lao PDR to determine whether the use of repellent and long-lasting insecticidal nets (LLINs) could reduce malaria more than LLINs alone. A total of 1,597 households, including 7,979 participants, were recruited in June 2009 and April 2010. Equal group allocation, stratified by village, was used to randomise 795 households to a 15% DEET lotion and the remainder were given a placebo lotion. Participants, field staff and data analysts were blinded to the group assignment until data analysis had been completed. All households received new LLINs. Participants were asked to apply their lotion to exposed skin every evening and sleep under the LLINs each night. Plasmodium falciparum and P. vivax cases were actively identified by monthly rapid diagnostic tests. Intention to treat analysis found no effect from the use of repellent on malaria incidence (hazard ratio: 1.00, 95% CI: 0.99–1.01, p = 0.868). A higher socio-economic score was found to significantly decrease malaria risk (hazard ratio: 0.72, 95% CI: 0.58–0.90, p = 0.004). Women were also found to have a reduced risk of infection (hazard ratio: 0.59, 95% CI: 0.37–0.92, p = 0.020). According to protocol analysis which excluded participants using the lotions less than 90% of the time found similar results with no effect from the use of repellent.

Conclusions

This randomised controlled trial suggests that topical repellents are not a suitable intervention in addition to LLINs against malaria amongst agricultural populations in southern Lao PDR. These results are also likely to be applicable to much of the Greater Mekong Sub-region.

Trial Registration

This trial is registered with number NCT00938379

Neem derivatives are not effective as toxic bait for tephritid fruit flies

Neem derivatives have been widely touted as replacements for pesticides. A feasible replacement of synthetic insecticides in the management of fruit flies could be to use neem products in baits. This study evaluated the bioactivity of neem (Azadirachta indica A. Juss) derivatives in bait for adults of Anastrepha fraterculus (Wiedemann) and Ceratitis capitata (Wiedemann). The estimated LCs50 values for A. fraterculus and C. capitata were 7,522 ppm (18.40 ppm of azadirachtin) and 1,368 ppm (3.35 ppm of azadirachtin), respectively, using an aqueous extract of neem seeds in bait after 10 d of experimentation. No significant differences in the mortality of A. fraterculus and C. capitata adults exposed to baits made from different extracts and neem oil were observed after 3 h or 2 or 6 d; differences among the treatments were observed only on the 10th day of the evaluation. We conclude that neem derivatives applied as a bait spray over citrus plants did not demonstrate a toxic effect on A. fraterculus and C. capitata. The reasons for the low efficacy of the neem bait on Tephritid fruit flies are discussed.

A repellent net as a new technology to protect cabbage crops

Floating row covers or insect-proof nets with fine mesh are effective at protecting vegetable crops against aphids but negatively impact plant health, especially under warm conditions. Furthermore, in control of cabbage insect pests, aphid parasitoids cannot enter the fine-mesh nets, leading to frequent aphid outbreaks. To surmount these difficulties, a 40-mesh-size repellent net treated with alphacypermethrin was studied in laboratory and field tests. Results showed both irritant and repellent effects of the alphacypermethrin-treated net on Myzus persicae (Sulzer) (Hemiptera: Aphididae) and its parasitoid Aphidius colemani (Haliday) (Hymenoptera: Braconidae). Under field conditions, there were no pests on cabbage protected with the repellent net. The repellent net allowed combining a visual and repellent barrier against aphids. Because of this additive effect, repellent nets allowed covering cabbage permanently with adequate protection against all pests.

Reduction of mosquito biting-pressure: spatial repellents or mosquito traps? A field comparison of seven commercially available products in Israel

The present study assessed the personal protection efficiency of seven commercially available mosquito control devices (MCD) under field conditions in Israel. Trials were performed in a high biting-pressure area inhabited by large populations of mosquito and biting midge species, using human volunteers as bait in landing catch experiments. Results show that under minimal air-movement, three spatial repellent based products (ThermaCELL(®) Patio Lantern, OFF!(®) PowerPad lamp, and Terminix(®) ALLCLEAR Tabletop Mosquito Repeller) significantly reduced the biting-pressure (t-test - P<0.01) when positioned at short distances from a volunteer (3, 7.5, and 10ft.), with the ThermaCELL unit being most effective (96.1, 89.9, and 76.66% reduction, respectively). No significant differences were seen between the three aforementioned devices at distances of 3 and 7.5ft., while at a distance of 10ft., only the ThermaCELL patio lantern repelled significantly more mosquitoes then the Terminix ALLCLEAR Tabletop Mosquito Repeller (t-test, P<0.05). In contrast, mosquito traps using attracting cues to bait mosquitoes (Dynatrap(®), Vortex(®) Electronic Insect Trap, Blue Rhino(®) SV3100) either significantly increased or had no effect on the biting-pressure at short distances compared with the unprotected control. Trials conducted over large areas showed that only the Blue Rhino trap was able to significantly reduce the biting-pressure (40.1% reduction), but this was only when operating four units at the corners of an intermediate sized area.

From Chemistry to Behavior. Molecular Structure and Bioactivity of Repellents against Ixodes ricinus Ticks

Tick-borne zoonoses are considered as emerging diseases. Tick repellents represent an effective tool for reducing the risk of tick bite and pathogens transmission. Previous work demonstrated the repellent activity of the phenylpropanoid eugenol against Ixodes ricinus; here we investigate the relationship between molecular structure and repellency in a group of substances related to that compound. We report the biological activity of 18 compounds varying for the presence/number of several moieties, including hydroxyl and methoxy groups and carbon side-chain. Each compound was tested at different doses with a bioassay designed to measure repellency against individual tick nymphs. Both vapor pressure and chemical features of the tested compounds appeared to be related to repellency. In particular, the hydroxyl and methoxy groups as well as the side-chain on the benzene ring seem to play a role. These results are discussed in light of available data on chemical perception in ticks. In the course of the study new repellent compounds were identified; the biological activity of some of them (at least as effective as the “gold standard” repellent DEET) appears to be very promising from a practical point of view.

Evaluation of the effectiveness of malaria vector control measures in urban settings of Dakar by a specific anopheles salivary biomarker

Standard entomological methods for evaluating the impact of vector control lack sensitivity in low-malaria-risk areas. The detection of human IgG specific to Anopheles gSG6-P1 salivary antigen reflects a direct measure of human–vector contact. This study aimed to assess the effectiveness of a range of vector control measures (VCMs) in urban settings by using this biomarker approach. The study was conducted from October to December 2008 on 2,774 residents of 45 districts of urban Dakar. IgG responses to gSG6-P1 and the use of malaria VCMs highly varied between districts. At the district level, specific IgG levels significantly increased with age and decreased with season and with VCM use. The use of insecticide-treated nets, by drastically reducing specific IgG levels, was by far the most efficient VCM regardless of age, season or exposure level to mosquito bites. The use of spray bombs was also associated with a significant reduction of specific IgG levels, whereas the use of mosquito coils or electric fans/air conditioning did not show a significant effect. Human IgG response to gSG6-P1 as biomarker of vector exposure represents a reliable alternative for accurately assessing the effectiveness of malaria VCM in low-malaria-risk areas. This biomarker tool could be especially relevant for malaria control monitoring and surveillance programmes in low-exposure/low-transmission settings.

The repellency of lemongrass oil against stable flies, tested using video tracking

Lemongrass oil (Cymbopogon citratus) is an effective repellent against mosquitoes (Diptera: Culicidae) and house flies (Diptera: Muscidae). In this study, its effectiveness was assessed on stable flies (Diptera: Muscidae) in laboratory conditions. First, we demonstrated that lemongrass oil is an active substance for antennal olfactory receptor cells of Stomoxys calcitrans as indicated by a significant increase in the electroantennogram responses to increasing doses of lemongrass oil. Feeding-choice tests in a flight cage with stable flies having access to two blood-soaked sanitary pads, one of which was treated with lemongrass oil, showed that stable flies (n = 24) spent significantly more time in the untreated zone (median value = 218.4 s) than in the treated zone (median value = 63.7 s). No stable flies fed on the treated pad, whereas nine fed on the untreated pad. These results suggest that lemongrass oil could be used as an effective repellent against stable flies. Additional studies to confirm its spatial repellent and feeding deterrent effects are warranted.

Biological activities of Zingiber officinale (Zingiberaceae) and Piper cubeba (Piperaceae) essential oils against pulse beetle, Callosobruchus chinensis (Coleoptera: Bruchidae)

Zingiber officinale (Zingiberaceae) and Piper cubeba (Piperaceae) was essential oils were investigated for repellent, insecticidal, antiovipositional, egg hatching, persistence of its insecticidal activities against pulse beetle, Callosobruchus chinensis (Coleoptera: Bruchidae). Essential oil vapours repelled bruchid adults significantly as oviposition was found reduced in choice oviposition assay. Z. officinale and P. cubeba essential oils caused both fumigant and contact toxicity in C. chinensis adults. In fumigation toxicity assay, median lethal concentrations (LC50) were 0.34 and 0.27 microL cm(-3) for Z. officinale and P. cubeba essential oils, respectively, while in contact toxicity assay, LC50 were 0.90 and 0.66 microL cm(-2) for Z. officinale and P. cubeba essential oils, respectively. These two essential oils reduced oviposition in C. chinensis adults when treated with sublethal concentrations by fumigation and contact method. Oviposition inhibition was more pronounced when adults come in contact than in vapours. Both essential oils significantly reduced egg hatching rate when fumigated. Persistence in insecticidal efficiency of both essential oils decreased with time. P. cubeba showed less persistence than Z. officinale essential oil because no mortality was observed in C. chinensis adults after 36 h of treatment with P. cubeba and after 48 h of treatment of Z. officinale essential oil. Fumigation with these essential oils has no effect on the germination of the cowpea seeds. Findings of the study suggest that Z. officinale and P. cubeba essential oils can be useful as promising agent in insect pest management programme.

Interruption of the semiochemical-based attraction of ambrosia beetles to ethanol-baited traps and ethanol-injected trap trees by verbenone

We examined the extent to which verbenone, a bark beetle antiaggregation pheromone, interrupted the semiochemical-based attraction of ambrosia beetles. Field trapping studies conducted in Ohio showed that a verbenone dispenser with a release rate of 50 mg/d at 25°C reduced the attraction of Anisandrus sayi Hopkins, Euwallacea validus (Eichhoff), Hypothenemus dissimilis (Zimmermann), Xylosandrus germanus (Blandford), and Xyleborinus saxesenii (Ratzeburg) to ethanol-baited traps. A verbenone dispenser attached to ethanol-injected Magnolia virginiana L. trap trees deployed in Ohio also reduced ambrosia beetle attacks compared to trap trees without a verbenone dispenser. Subsequent field trials demonstrated a direct relationship between distance from a verbenone dispenser and ambrosia beetle attacks on trap trees in Ohio in 2011 and 2012 and Tennessee in 2012, but not in Tennessee and Virginia in 2011. Assessment of the influence of verbenone on the probability of attacks above a density threshold found that although attacks occurred on trap trees regardless of their proximity to a verbenone dispenser, the higher density of attacks per tree occurred on trap trees farthest away from the verbenone source in Ohio and Tennessee. Verbenone alone could be somewhat useful for discouraging ambrosia beetle attacks on individual trees or on a small spatial scale, but deployment of verbenone might be most effective when integrated as part of a "push-pull" strategy.

Biting deterrence and insecticidal activity of hydrazide-hydrazones and their corresponding 3-acetyl-2,5-disubstituted-2,3-dihydro-1,3,4-oxadiazoles against Aedes aegypti

BACKGROUND

Taking into account the improvement in insecticidal activity by the inclusion of fluorine in the hydrazone moiety, the authors synthesized new 4-fluorobenzoic acid hydrazides and 3-acetyl-2,5-disubstituted-2,3-dihydro-1,3,4-oxadiazoles, substituting a phenyl group or a heteroaryl ring carrying one or two atoms of F, Cl and Br, and investigated their biting deterrent and larvicidal activities against Aedes aegypti for the first time.

RESULTS

The compound 3-acetyl-5-(4-fluorophenyl)-2-[4-(dimethylamino)phenyl]-2,3-dihydro-1,3,4-oxadiazole (17) produced the highest biting deterrent activity (BDI = 1.025) against Ae. Aegypti, followed by 4-fluorobenzoic acid [(phenyl)methylene] hydrazide (1). These activity results were similar to those of N,N-diethyl-meta-toluamide (DEET), which showed a proportion not biting of 0.8-0.92. When compounds 1 and 17 were tested on cloth worn on human volunteers, compound 1 was not repellent for some volunteers until present in excess of 500 nmol cm(-2) , while compound 17 was not repellent at the highest concentration tested (1685 nmol cm(-2) ). In the larvicidal screening bioassays, only compounds 10, 11, 12 and 17 showed 100% mortality at the highest screening dose of 100 ppm against Ae. aegypti larvae. Compounds 11 and 12 with LD50 values of 24.1 and 30.9 ppm showed significantly higher mortality than 10 (80.3 ppm) and 17 (58.7 ppm) at 24-h post-treatment.

CONCLUSION

The insecticidal and biting deterrent activities were correlated with the presence of a halogen atom on the phenyl or heteroaryl substituent of the hydrazone moiety.

Effect of Aedes aegypti exposure to spatial repellent chemicals on BG-Sentinel™ trap catches

BACKGROUND

An integrated approach to reduce densities of adult Aedes aegypti inside homes is currently being evaluated under experimentally controlled field conditions. The strategy combines a spatial repellent (SR) treatment (applied indoors) with the Biogents Sentinel™ (BGS) mosquito trap positioned in the outdoor environment. In essence, when combined, the goal is to create a push-pull mechanism that will reduce the probability of human-vector contact. The current study measured BGS recapture rates of Ae. aegypti test cohorts that were exposed to either SR or control (chemical-free) treatments within experimental huts. The objective was to define what, if any, negative impact SR may have on BGS trap efficacy (i.e., reduced BGS collection).

METHODS

Aedes aegypti females were exposed to SR compounds within experimental huts in the form of either treated fabric (DDT and transfluthrin) or mosquito coil (metofluthrin). Test cohorts were released within individual screen house cubicles, each containing 4 BGS traps, following SR exposure according to treatment. Two separate test cohorts were evaluated: (i) immediate release (IR) exposed from 06:00-12:00 hours and released at 12:00 hours and (ii) delayed release (DR) exposed from12:00-18:00 hours and released at 05:30 hours the following day. BGS recapture was monitored at 09:30, 13:30 and 15:30 hours and the cumulative recapture by time point quantified.

RESULTS

Exposure of Ae. aegypti females to either DDT or metofluthrin did not significantly impact BGS capture as compared to cohorts of non-exposed females. This was true for both IR and DR exposure populations. IR cohorts exposed to transfluthrin resulted in significantly lower BGS recapture compared to matched controls but this effect was primarily due to high mosquito mortality during transfluthrin trials.

CONCLUSION

Our data indicate no more than minor and short-lived impacts (i.e., reduced attraction) on BGS trap catches following exposure to the pyrethroid compounds transfluthrin and metofluthrin and no change in recapture densities using DDT as compared to matched controls. These findings suggest a combined SR and BGS approach to vector control could function as a push-pull strategy to reduce Ae. aegypti adults in and around homes.

Repellency of DEET, picaridin, and three essential oils to Triatoma rubida (Hemiptera: Reduviidae: Triatominae)

The kissing bug, Triatoma rubida (Uhler) is a common hematophagous bug in Tucson, AZ, and is responsible for causing severe allergic reactions in some bitten individuals. DEET, picaridin, tea tree oil, peppermint oil, and citronella oil were tested for repellency to T. rubida and its ability to probe and feed on a small restrained rat. No long range repellency was observed with any of the test materials. The lowest repellent concentrations observed were: 10% DEET, 7% picaridin; 30% tea tree oil, 3.3% peppermint oil, and 0.165% citronella oil. Only citronella oil was able to stop all probing and feeding by T. rubida. Citronella oil appears to be a promising potential repellent to prevent sleeping people from being bitten by kissing bugs.

Repellency of cassia bark, eucalyptus, and star anise oils and their major constituents to Leptotrombidium pallidum (Acari: Trombiculidae)

Leptotrombidium pallidum (Nagoya, Miyagawa, Mitamura & Tamiya) is a primary vector of Orientia tsutsugamushi (Hyashi), the causative agent of scrub typhus. An assessment is made of the repellency to L. pallidum larvae (chiggers) of cassia bark, eucalyptus, and star anise oils and major constituents (E)-cinnamaldehyde, 1,8-cineole, and (E)-anethole of the corresponding oils. Results were compared with those of conventional repellents DEET (N,N-diethyl-3-methylbenzamide), IR3535 [(ethyl 3-[acetyl(butyl)amino]propanoate)], and permethrin. Based on the median repellent concentration (RC50) values, (E)-cinnamaldehyde, (E)-anethole, cassia bark oil, and star anise oil (RC50, 0.95-1.52 mg/cm2) exhibited significantly more potent repellency than DEET (3.85 mg/cm2). (E)-cinnamaldehyde, (E)-anethole, cassiabark oil, 1,8-cineole, and star anise oil were approximately 43, 16, 11, 8, and 4 times more effective than IR3535 (CC5, 6.51%) as judged by the median climbing distance-disturbing concentration (CC50) values. The median residual duration time of repellency (RT50) was significantly more pronounced in DEET (RT50, 323 min) than in all essential oils and constituents (108-167 min). In the light of global efforts to reduce the level of highly toxic synthetic repellents, the three essential oils and their major constituents described merit further study as potential biorepellents for the control of L. pallidum populations.

Synthesis and biological activity of substituted urea and thiourea derivatives containing 1,2,4-triazole moieties

A series of novel thiourea and urea derivatives containing 1,2,4-triazole moieties were synthesized and evaluated for their antifungal and larvicidal activity. Triazole derivatives 3a-e and 4a-e were synthesized by reacting thiocarbohydrazide with thiourea and urea compounds 1a-e and 2a-e, respectively, in a 130-140 °C oil bath. The proposed structures of all the synthesized compounds were confirmed using elemental analysis, UV, IR, 1H-NMR and mass spectroscopy. All compounds were evaluated for antifungal activity against plant pathogens, larvicidal and biting deterrent activity against the mosquito Aedes aegypti L. and in vitro cytotoxicity and anti-inflammatory activity against some human cell lines. Phomopis species were the most sensitive fungi to these compounds. Compounds 1b, 1c, 3a and 4e demonstrated selectively good activity against Phomopis obscurans and only 1b and 4e showed a similar level of activity against P. viticola. Compound 3d, with a LD50 value of 67.9 ppm, followed by 1c (LD50 = 118.8 ppm) and 3e (LD50 = 165.6 ppm), showed the highest toxicity against Aedes aegypti larvae. Four of these compounds showed biting deterrent activity greater than solvent control, with the highest activity being seen for 1c, with a proportion not biting (PNB) value of 0.75, followed by 1e, 2b and 1a. No cytotoxicity was observed against the tested human cancer cell lines. No anti-inflammatory activity was observed against NF-kB dependent transcription induced by phorbol myristate acetate (PMA) in human chondrosarcoma cells.

Operational use of household bleach to "crash and release" Aedes aegypti prior to Wolbachia-infected mosquito release

Dengue (family Flaviviridae, genus Flavivirus, DENV) remains the leading arboviral cause of mortality in the tropics. Wolbachia pipientis has been shown to interrupt DENV transmission and is presently being trialled as a biological control. However, deployment issues have arisen on methods to temporarily suppress wild mosquito populations before Wolbachia-infected mosquito releases. By suppressing wild populations, fewer Ae. aegypti releases are required to achieve a sustainable Wolbachia density threshold. Furthermore, public distress is reduced. This study tests the application of domestic bleach (4% NaCIO) to temporarily "crash" immature Aedes populations in water-filled containers. Spray application NaClO (215 ppm) resulted in a mean 48-h mortality of 100, 100, 97, and 88% of eggs, second-instar larvae, fourth-instar larvae, and pupae, respectively. In the field, NaClO delayed ovipositing by 9 d in cooler months, and 11 d in hotter months, after which oviposition resumed in treated receptacles. We found bleach treatment of pot-plant bases did not cause wilting, yellowing, or dropping of leaves in two ornamental plants species. Domestically available NaClO could be adopted for a "crash and release" strategy to temporarily suppress wild populations of Ae. aegypti in containers before release of Wolbachia-infected mosquitoes. The "crash and release" strategy is also applicable to other mosquito species, e.g., Aedes albopictus (Skuse), in strategies using released mosquitoes.

Formulas of components of citronella oil against mosquitoes (Aedes aegypti)

The mosquito Aedes aegypti is an epidemic vector of several diseases such as dengue fever and yellow fever. Several pesticides are used to control the mosquito population. Because of their frequent use, some mosquitoes have developed resistance. In this study, we used the Y-tube olfactometer to test essential oils of Cymbopogon species and screened specific formulas of components as repellents against Ae. aegypti. At 400 μL, the extracted oil of citronella grass (Cymbopogon nardus) and myrcene produced a low-active response by inhibiting mosquito host-seeking activity. Citronella grass, lemon grass (Cymbopogon citratus), citral and myrcene also produced a low-treatment response to repellents, for more potential to affect host-seeking behavior. Furthermore, the mixture of citral, myrcene, and citronellal oil (C:M:Ci = 6:4:1) greatly affected and inhibited host-seeking behavior (76% active response; 26% treatment response with 40 μL; 42.5%, 18% with 400 μL; and 19%, 23% with 1000 μL). As compared with the result for N,N-diethyl-3-methylbenzamide (DEET; 44%, 22% with 400 μL), adjusting the composition formulas of citronella oil had a synergistic effect, for more effective repellent against Ae. aegypti.

A field bioassay to evaluate potential spatial repellents against natural mosquito populations

A field bioassay evaluating candidate chemicals as aerial repellents was developed and evaluated against natural mosquito populations in Beltsville, MD. The bioassay consisted of an attractive source surrounded by a grid of 16 septa containing a volatile candidate aerial repellent, compared with an attractive source without such a grid. The attractive source was a Centers for Disease Control and Prevention light trap supplemented with carbon dioxide. Significant sources of variation included weather, position, and the differential response of mosquito species. Despite these sources of variation, significant repellent responses were obtained for catnip oil, E,Z-dihydronepetalactone, and DEET.

Repellents inhibit P450 enzymes in Stegomyia (Aedes) aegypti

The primary defence against mosquitoes and other disease vectors is often the application of a repellent. Despite their common use, the mechanism(s) underlying the activity of repellents is not fully understood, with even the mode of action of DEET having been reported to be via different mechanisms; e.g. interference with olfactory receptor neurones or actively detected by olfactory receptor neurones on the antennae or maxillary palps. In this study, we discuss a novel mechanism for repellence, one of P450 inhibition. Thirteen essential oil extracts from Colombian plants were assayed for potency as P450 inhibitors, using a kinetic fluorometric assay, and for repellency using a modified World Health Organisation Pesticide Evaluations Scheme (WHOPES) arm-in cage assay with Stegomyia (Aedes) aegypti mosquitoes. Bootstrap analysis on the inhibition analysis revealed a significant correlation between P450-inhibition and repellent activity of the oils.

Field evaluation of repellency of a polyherbal essential oil against blackflies and its dermal toxicity using rat model

In the present study we have evaluated the repellent activity of mixture of Curcuma longa, Zanthoxylum limonella and Pogostemon heyneanus essential oils in 1:1:2 ratio at 5%, 10% and 20% concentration against blackflies in northeastern India. Initially the essential oil mixture tested here has been found effective against Aedes albopictus mosquitoes. The average protection recorded in 20% concentration (170.56 ± 4.0; 95% CI = 162.09-179.02) was higher as compared to other two concentrations (F = 90.2; p<0.0001; df = 53). Percentage repellency and repellency index was found to be higher in 20% concentration (p ≤ 0.017). No appreciable clinical and behavioral signs were observed in the acute dermal toxicity using rat model. No changes were observed in biochemical profiles of treatment group animals. Similarly, no prominent lesions were observed in vital organs of treatment in both the sexes. The study concludes that tested repellent is safe for use and has multi-insects repellent property.

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

Thymus magnus, an endemic species, is found in the Republic of Korea. The volatile compounds extracted by SPME from T. magnus were investigated for their chemical composition and electrophysiological response against the Asian tiger mosquito, Aedes albopictus. The volatile compounds of T. magnus as determined by gas chromatography mass spectrometry were gamma-terpinene (33.0%), thymol (29.9%), beta-bisabolene (8.9%), p-cymene (8.3%), alpha-terpinene (5.0%), myrcene (4.7%), beta-caryophyllene (4.0%), alpha-thujene (2.7%), camphene (1.3%), carvacrol (1.2%), and alpha-pinene (1.1%). Among these candidates, thymol exhibited complete (100%) repellent activity against female Ae. albopictus, an effect that was confirmed through evaluating the electrophysiological response on the antenna of Ae. albopictus. The effectiveness of a binary 1:2 mixture of thymol and vanillin (0.05:0.1 microl per cm2) was found to be significantly more effective than thymol alone for a period of 120 min. In addition, thymol, alpha-terpinene, and carvacrol showed high larvicidal activity against on the third-stage larvae with LC50 values of 0.9 microl per 100 ml.