Adenosine triphosphate overrides the aversive effect of antifeedants and toxicants: a model alternative phagostimulant for sugar-based vector control tools.

BACKGROUND: Sugar, when used as the phagostimulant in attractive toxic bait control tools, limits the efficacy and selectivity of this technology. Thus, more potent and selective phagostimulants than sugar are required to improve this technology. The potency of adenosine triphosphate (ATP) as an alternative model phagostimulant was assessed to determine its capacity to override the aversive effects of select antifeedants and toxicants. How ATP and sucrose modulate the rate of toxicity in the yellow fever mosquito Aedes aegypti was also examined. METHODS: A no-choice feeding assay was used to investigate the phagostimulatory ability of ATP to override the aversive effects of structurally divergent antifeedant and toxicant compounds, and to modulate the rate of toxicity over 24 h. Binary combinations of antifeedant and toxicant compounds, at various concentrations, were similarly assessed for enhanced lethal potency. In comparison, no-choice open access and cotton wick feeding assays were used to determine the phagostimulatory role of sucrose in the ingestion of boric acid-laced diets. Dissections of the guts were performed to determine the diet destination as dependant on the phagostimulant. RESULTS: ATP is a potent phagostimulant that dose dependently overrides aversion to antifeedant and toxicant tastants. Feeding on antifeedant- or toxicant-laced diets that was induced by ATP selectively resulted in rapid knockdown (nicotine, lobeline and caffeine) or death (boric acid and propylene glycol), with a combination of the two lethal compounds inducing a synergistic effect at lower concentrations. ATP- and sucrose-induced feeding predominantly directed the antifeedant- or toxicant-laced meals to the midgut and the crop, respectively. CONCLUSIONS: ATP is an efficacious alternative model phagostimulant to sucrose that overrides the aversive effects of antifeedants and toxicants, resulting in rapid toxic effects. Furthermore, this study demonstrates that variation in the rate of toxicity between ATP- and sugar-induced feeding is at least partly regulated by the differential feeding response, volume imbibed and the destination of the meals. Additional research is needed to identify structurally related, stable analogues of ATP due to the ephemeral nature of this molecule. For future applications, the workflow presented in this study may be used to evaluate such analogues for their suitability for use in attractive bait stations designed to target a broad range of haematophagous arthropods and prevent off-target species' feeding.

Identification of Bioactive Volatile Organic Compounds Using Combined Gas Chromatography and Single Sensillum Recording.

Most arthropods rely heavily on their sense of smell (i.e., olfaction) to locate and discriminate among mates, food, and egg laying sites. The odors emanating from these resources are composed of blends of volatile compounds that are detected by olfactory sensory neurons (OSNs) that are housed in hair-like structures, called sensilla, on the olfactory organs of arthropods. By inserting an electrode into a single sensillum and recording the activity of the OSNs while stimulating with volatile compounds eluting from a gas chromatograph, combined gas chromatography and single sensillum recording (GC-SSR) provides a high-resolution tool to identify bioactive compounds and to functionally characterize the peripheral olfactory system of arthropods.

Combined Gas Chromatography and Single Sensillum Recording for Mosquitoes.

Combined gas chromatography and single sensillum recording (GC-SSR) joins together the established volatile compound separation and relative quantification techniques of GC with the ability to functionally screen olfactory sensory neurons (OSNs) for volatile selectivity and sensitivity using SSR. With minimal equipment modification, including a splitter and a heated transfer line, half of the effluent from the gas chromatograph column is directed to the flame ionization detector and half to the mosquito antennae. This GC-SSR combination provides a bioassay capable of determining the salient natural ligands for individual OSNs and of providing accurate and comparable dose-response curves irrespective of differences in the volatility of the compounds.