Exploiting nectar and blood feeding cues and phagostimulants to optimise Attractive Targeted Sugar Baits against a sand fly vector of leishmaniasis.

Abstract

BackgroundLeishmaniasis presents a major public health problem for a large number of countries requiring effective integrated management of the vector, sand flies, for sustained control. Such strategies need to be economically and environmentally sustainable and adaptable to the behaviour of local vectors. One such tool is Attractive Targeted Sugar Baits (ATSB) that exploit the necessity of sand flies to acquire sugars between bloodmeals. Here we explored the kinetics and cues for sugar and blood feeding to improve the efficacy of ATSBs against sand flies. MethodsA fluorescent assay was developed to quantify sugarmeals to assess the feeding efficiency of colony-reared female Lutzomyia longipalpis sand flies. ResultsSand flies showed a range of preferences for different sugars presented on cotton wool and could be manipulated to deposit them into the crop and/or midgut. We found that the combination of 10% sucrose and 10% fructose allowed flies to obtain the largest sugarmeals taken to the crop. Sugarmeals were taken to both the crop and midgut when it contained 200 mM bovine serum albumin (BSA) as a source of protein and 1 mM adenosine triphosphate (ATP) as a phagostimulant. Using this combination, the efficacy of the ingested insecticide fipronil was significantly increased; reducing the 50% lethal concentration from 584 {micro}M to 1.65 {micro}M in a sugarmeal that promoted the simultaneous uptake of the insecticide into the midgut as well as the crop. ConclusionsIn this study we highlight the potential of understanding the cues used by vectors to sugar feed and blood feed. By incorporating blood feeding phagostimulants, such as BSA and ATP, in ATSB we vastly improve their killing efficiency against sand flies. This demonstrates a new approach to target these disease vectors. Author SummaryMany insect vectors of disease use sugars, such as nectar, as fuel to enable them to obtain blood, that in turn sustains parasite transmission. In most blood feeding Diptera sugars are diverted to the crop where it is stored and released into the midgut for energy whereas blood is taken directly to the midgut where it is digested to provide nutrients for egg development. For sand flies the cues required to switch between sugar and blood feeding programmes are unknown but if they were they could be exploited to improve Attractive Targeted Sugar Baits (ATSB) as a means of poisoning sand flies when they sugar feed. In this study we find that the sand fly, Lutzomyia longipalpis, uses a combination of physical cues (biting/piercing vs sucking) and meal composition to allow them to efficiently feed on nectar and blood. We show that they sense protein and adenosine triphosphate (ATP) to direct blood to the midgut and we demonstrate that this can be turned to our advantage to improve the lethality of ATSB. We show that inclusion of bovine serum albumin as a source of protein and the phagostimulant ATP can trick sand flies to blood feed on sugar and direct the insecticide fipronil to the midgut where it was 355-fold more potent than in sugar alone. These results show the potential of phagostimulants to improve the efficacy and selectivity of ATSB towards blood feeding arthropods, including sand flies, and highlights the value of understanding the feeding programmes of disease vectors in general.