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.

Multi-Omic Analysis of Symbiotic Bacteria Associated With Aedes aegypti Breeding Sites

“…Short-chain fatty acids, like isovaleric acid and butyric acid, have been shown to act as deterrents to ovipositing females of Culex spp. and Aedes albopictus (Hwang et al, 1980;Boullis et al, 2021). Likewise, aromatic compounds like indole mediate oviposition of Anopheles gambiae and Culex spp.…”

“…Metabolites of bacterial origin, particularly from Klebsiella (or other related taxa with similar metabolic outputs) could act as guiding and/or decision-making modulating sensory cues (either olfactory or gustatory) for other conspecific females to access the quality of the breeding site ( Ponnusamy et al, 2008 ; Boullis et al, 2021 and references therein). It is known that Klebsiella is present in larvae-positive breeding sites ( Dada et al, 2014 ) and that bacteria from this genus produce volatile compounds ( Rees et al, 2017 ).…”

“…As thriving larvae alter their niche, potentially modifying the microbial composition ( Scolari et al, 2021 ), these bacteria-derived volatile compounds could accumulate in the headspace of the water. Identifying the nature of these molecules, and using them in chemical ecology and behavioral assays seems to be a promising avenue to explore, as Boullis et al (2021) recently highlighted, due to the fact that their mechanism of action has not yet been elucidated.…”

Semiochemical oviposition cues to control Aedes aegypti gravid females: state of the art and proposed framework for their validation

“…Pentadecanoic acid and the blend of compounds at a ratio mimicking the one observed in larvae induced significant stimulation, with OAI values of 0.38 at 10 ppm for pentadecanoic acid and 0.21 at 1 ppm for the blend. Interestingly, these candidates were as efficient for inducing oviposition as the water that previously contained larvae [ 61 ].…”

“…In this context, some compounds originating from mosquito immature stages were tested for their potential in deterring oviposition. First, myristoleic acid, a long-chain fatty acid identified in larval extracts, induced high oviposition deterrence, with an OAI of −0.70 at 100 ppm [ 61 ]. Interestingly, all the esters identified in mosquito eggs, such as methyl dodecanoate and methyl (Z)-9-hexadecenoate, were deterrents for females, with OAI values of −0.92 and −0.86, respectively, at 100 ppm [ 47 ].…”