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Behavioural and antennal responses of Aedes aegypti (l.) (Diptera: Culicidae) gravid females to chemical cues from conspecific larvae.

ABSTRACT: Mass trapping of gravid females represents one promising strategy for the development of sustainable tools against Aedes aegypti. However, this technique requires the development of effective odorant lures that can compete with natural breeding sites. The presence of conspecific larvae has been shown to stimulate oviposition. Hence, we evaluated the role of four major molecules previously identified from Ae. aegypti larvae (isovaleric, myristoleic, myristic [i.e. tetradecanoic], and pentadecanoic acids) on the oviposition of conspecific females, as well as their olfactory perception to evaluate their range of detection. Using flight cage assays, the preference of gravid females to oviposit in water that previously contained larvae (LHW) or containing the four larval compounds was evaluated. Then, compounds and doses inducing the highest stimulation were challenged for their efficacy against LHW. Only isovaleric acid elicited antennal response, suggesting that the other compounds may act as taste cues. Pentadecanoic acid induced significant oviposition stimulation, especially when dosed at 10 ppm. Myristoleic acid and isovaleric acid deterred oviposition at 10 and 100 ppm, while no effect on oviposition was observed with myristic acid irrespectively of the dose tested. When the four compounds were pooled to mimic larvae's chemical signature, they favored oviposition at 1 ppm but negatively affected egg-laying at higher concentrations. When properly dosed, pentadecanoic acid and the blend of compounds may be promising lures for ovitraps as they could compete with LHW. Due to their low volatility, their effect should be further evaluated under field conditions, in addition with long-range attractants for developing effective tools against gravid females.

SUBMITTER: Boullis A

PROVIDER: S-EPMC7904138 | biostudies-literature | 2021

REPOSITORIES: biostudies-literature

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Behavioural and antennal responses of Aedes aegypti (l.) (Diptera: Culicidae) gravid females to chemical cues from conspecific larvae.

Boullis Antoine A Mulatier Margaux M Delannay Christelle C Héry Lyza L Verheggen François F Vega-Rúa Anubis A

PloS one 20210224 2

Mass trapping of gravid females represents one promising strategy for the development of sustainable tools against Aedes aegypti. However, this technique requires the development of effective odorant lures that can compete with natural breeding sites. The presence of conspecific larvae has been shown to stimulate oviposition. Hence, we evaluated the role of four major molecules previously identified from Ae. aegypti larvae (isovaleric, myristoleic, myristic [i.e. tetradecanoic], and pentadecanoi ...[more]

PMID: 33626104

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Project description:BackgroundDescribing spatio-temporal occurrence and habitat characteristics of Aedes mosquito larvae is crucial for the control of Aedes borne viral diseases. This study assessed spatio-temporal abundance and habitat characteristics of Aedes larvae in the Southern Afar Region, Ethiopia.MethodsImmature mosquitoes were surveyed in Awash Sebat, Awash Arba, and Werer towns of the Southern Afar Region once per month from May 2022 to April 2023. Larvae and pupae surveys were carried out along the available water-holding containers. The collected larvae/pupae were reared to adults and identified by species/genus morphologically. The physical and chemical properties of the habitats were also characterized.ResultsA total of 9099 Aedes larvae/pupae were collected, of which 53.6% (4875) were from Awash Sebat, 29.5% (2687) from Awash Arba and 16.9% (1537) from Werer. Water-holding tyres harboured the highest number of Aedes larvae/pupae followed by water-storage drums. All the Aedes larvae/pupae reared to adults were morphologically identified as Aedes aegypti. The overall Container Index was 47.28%, House Index 18.19%, Breteau Index 59.94% and Pupal Index 171.94. Significant positive relations were observed in the occurrences of Ae. aegypti larvae/pupae with water-holding tyre (AOR = 15.89, CI = 3.55-71.09, p < 0.001), water storage drums (AOR = 19.84, CI = 4.64-84.89, p < 0.001), domestic habitat (AOR = 3.76, CI = 1.27-11.12, p = 0.017), and significant negative relations were observed with Ae. aegypti larvae/pupae occurrence and tap water source (AOR = 0.08, CI = 0.02-0.31, p = 0.001). Ae. aegypti larvae/pupae densities showed positive relations with dissolved oxygen (β = 0.523, p < 0.001) and total hardness (β = 0.475, p = 0.034) of water.ConclusionsDiverse types of artificial water-holding containers were positive for Ae. aegypti larvae/pupae. Ae. aegypti larvae/pupae were abundant in used water-holding tyres, water storage drums, and cement tanks in Awash Sebat, Awash Arba, and Werer towns. This could put the residents of the towns at high risk of infections with Ae. aegypti transmitted viral diseases such as chikungunya and dengue outbreaks. Thus, we recommend artificial water-holding container management as a strategy to control Ae. aegypti and hence the arboviral diseases transmission.

Project description:BackgroundAedes aegypti, which is widely distributed in the Lao People's Democratic Republic (PDR), is the primary vector of arboviral diseases. Chemical insecticides have been intensively used to eliminate mosquito-borne diseases, resulting in the development of insecticide resistance. However, little is known about the insecticide resistance of mosquito populations in Lao PDR and the mechanisms responsible for it, which have important implications for vector management programs. Here, we examined the phenotypic and haplotypic profiles of insecticide resistance in populations of Ae. aegypti larvae from central Lao PDR.MethodsAe. aegypti larvae were collected from four sites in Lao PDR, and their susceptibility to temephos, deltamethrin, permethrin, and Bacillus thuringiensis israelensis (Bti) was tested using larval bioassays. Synergistic tests were also conducted to evaluate the activity of insecticide-metabolizing enzymes in the larvae. Deltamethrin-resistant and Deltamethrin-susceptible larvae were then genotyped for knockdown resistance (kdr) mutations to determine the associations between each genotype and resistance.ResultsAe. aegypti larvae from central Lao PDR were considered to be "resistant" (<98% mortality) to organophosphates and pyrethroids. The bio-insecticide Bti remains effective against such larvae. The resistance mechanisms of Ae. aegypti larvae were found to vary among populations, especially for pyrethroid resistance. Kdr mutations were significantly associated with deltamethrin resistance in Ae. aegypti from the Xaythany population. In contrast, synergist assays with piperonyl butoxide suggested that cytochrome P450 monooxygenases played an important role in the resistance seen in the Khounkham and Thakhek populations.ConclusionThis study obtained information that will aid the design and implementation of insecticide-based vector management of Ae. aegypti in central Lao PDR. Ae. aegypti larvae from central Lao PDR were highly susceptible to Bti, while they were resistant to temephos at a diagnostic dose of 0.0286 mg/L. Given the limited number of insecticides that are approved for vector control, it is important to alternate between temephos and other larvicides, such as Bti and pyriproxyfen. The differences in pyrethroid resistance mechanisms seen among the Ae. aegypti populations highlight the need to tailor vector-control strategies to each region to increase the success of dengue control in Lao PDR.

Project description:BackgroundThe entomopathogenic fungus Metarhizium anisopliae is a candidate for the integrated management of the disease vector mosquito Aedes aegypti. Metarhizium anisopliae is pathogenic and virulent against Ae. aegypti larvae; however, its half-life is short without employing adjuvants. Here, we investigated the use of neem oil to increase virulence and persistence of the fungus under laboratory and simulated field conditions.MethodsNeem was mixed with M. anisopliae and added to recipients. Larvae were then placed in recipients at 5-day intervals for up to 50 days. Survival rates were evaluated 7 days after exposing larvae to each treatment. The effect of neem on conidial germination following exposure to ultraviolet radiation was evaluated under laboratory conditions. Statistical tests were carried out using ANOVA and regression analysis.ResultsLaboratory bioassays showed that the fungus alone reduced survival to 30% when larvae were exposed to the treatment as soon as the suspension had been prepared (time zero). A mixture of fungus + neem resulted in 11% survival at time zero. The combination of fungus + neem significantly reduced larval survival rates even when suspensions had been maintained for up to 45 days before adding larvae. For simulated-field experiments 1% neem was used, even though this concentration is insecticidal, resulting in 20% survival at time zero. However, this toxic effect was reduced over time. When used alone under simulated-field conditions the fungus rapidly lost virulence. The formulation fungus + neem effectively maintained fungal virulence, with larval survival rates significantly reduced for up to 45 days after preparation of the suspensions. The effective half-life of the fungus or neem when used separately was 6 and 13 days, respectively. The half-life of fungus formulated in 1% neem was 34 days. Conidia suspended in neem maintained high levels of germination even following a 2-h exposure to ultraviolet radiation.ConclusionsA combination of the entomopathogenic fungus M. anisopliae with neem oil effectively increases the half-life and virulence of the fungus when tested against Ae. aegypti larvae, even under simulated field conditions. Neem oil also protected the fungus from the damaging effects of ultraviolet radiation.

Dataset Information

Behavioural and antennal responses of Aedes aegypti (l.) (Diptera: Culicidae) gravid females to chemical cues from conspecific larvae.

Publications

Behavioural and antennal responses of Aedes aegypti (l.) (Diptera: Culicidae) gravid females to chemical cues from conspecific larvae.

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