Phagostimulatory dynamics of adenine nucleotides in mosquitoes

The mosquitoes Aedes aegypti and Anopheles gambiae are vectors of major medical importance, incriminated in over half a million lives lost annually. While there has been significant focus on understanding the olfaction mechanisms underlying host-seeking in mosquitoes for the development of odour-based control tools, little is known about the mechanisms underlying gustation in blood feeding, the ultimate behaviour in the change of events leading up to disease transmission. An increased understanding of these gustatory mechanisms may be vital for advancing taste-based alternative vector control tools. Using a no-choice membrane feeding assay (papers II, III, and IV) and a spectrophotometric analysis (paper II), the feeding response of the two vectors to blood-derived adenine nucleotide diets, as proxies, and a reliable signal, for blood, was examined. While these experiments revealed that Ae. aegypti is more sensitive than An. gambiae (paper II) to the adenine nucleotide diets, both species maintained the same selectivity to the diets, with a dose-dependent bimodal feeding pattern. The latter expands the all-or-none blood-feeding theory for haematophagous arthropods to include an initial tasting step (paper II). Adenine nucleotides also regulated the proportion of An. gambiae prediuresing in a dose-dependent manner, but did not affect the volume engorged or prediuresed (paper II). A transcriptome analysis of the labrum identified putative genes that are involved in the detection and assessment of blood modalities (paper III). A shift from a high abundance of genes with structural function in the teneral age libraries to genes with cellular, neuro-communicative and modulatory function, including putative ATP receptors, in the 3 days-post-eclosion libraries was observed, providing blood feeding mosquitoes with a structurally sturdy and chemosensory-competent blood feeding organ (paper IV).  The assessment of whether the ATP sensory pathway may be a viable way of overcoming the aversive effects of antifeedants and toxicants revealed its superiority over the sugar sensory pathway. ATP induced a reflexive engorgement on toxic meals, which were directed to the midgut, in contrast to sugar-induced meals, which were directed to the crop, an observation that correlated with the rapid mortality rates. Taken together, this study expanded our mechanistic understanding of the phagostimulatory dynamics of adenine nucleotides in Ae. aegypti and An. gambiae, and the associated putative labral detection receptors in Ae. aegypti, with the establishment of a novel workflow for advancing taste-based vector control tools

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

BackgroundSugar, 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.MethodsA 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.ResultsATP 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.ConclusionsATP 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

Novel Viruses Found in Antricola Ticks Collected in Bat Caves in the Western Amazonia of Brazil

In this study, we describe the viral composition of adult Antricola delacruzi ticks collected in a hot bat cave in the state of Rondonia, Western Amazonia, Brazil. A. delacruzi ticks, are special, compared to many other ticks, in that they feed on both bats (larval blood feeding) and bat guano (nymphal and adult feeding) instead of feeding exclusively on vertebrate hosts (blood feeding). Considering this unique life-cycle it is potentially possible that these ticks can pick up/be infected by viruses not only present in the blood of viremic bats but also by virus shed through the bat guano. The viral metagenomic investigation of adult ticks showed that single-stranded negative-sense RNA viruses were the dominant group of viruses identified in the investigated ticks. Out of these, members of the Nairoviridae family were in clear majority constituting 88% of all viral reads in the data set. Genetic and phylogenetic analyses indicate the presence of several different orthonairoviruses in the investigated ticks with only distant relationship to previously described ones. In addition, identification of viral sequences belonging to Orthomyxoviridae, Iflaviridae, Dicistroviridae, Polycipiviridae, Reoviridae and different unclassified RNA viruses showed the presence of viruses with low sequence similarity to previously described viruses

Novel Viruses Found in Antricola Ticks Collected in Bat Caves in the Western Amazonia of Brazil

In this study, we describe the viral composition of adult Antricola delacruzi ticks collected in a hot bat cave in the state of Rondônia, Western Amazonia, Brazil. A. delacruzi ticks, are special, compared to many other ticks, in that they feed on both bats (larval blood feeding) and bat guano (nymphal and adult feeding) instead of feeding exclusively on vertebrate hosts (blood feeding). Considering this unique life-cycle it is potentially possible that these ticks can pick up/be infected by viruses not only present in the blood of viremic bats but also by virus shed through the bat guano. The viral metagenomic investigation of adult ticks showed that single-stranded negative-sense RNA viruses were the dominant group of viruses identified in the investigated ticks. Out of these, members of the Nairoviridae family were in clear majority constituting 88% of all viral reads in the data set. Genetic and phylogenetic analyses indicate the presence of several different orthonairoviruses in the investigated ticks with only distant relationship to previously described ones. In addition, identification of viral sequences belonging to Orthomyxoviridae, Iflaviridae, Dicistroviridae, Polycipiviridae, Reoviridae and different unclassified RNA viruses showed the presence of viruses with low sequence similarity to previously described viruses