Is Anopheles gambiae attraction to floral and human skin-based odours and their combination modulated by previous blood meal experience?

Elison E Kemibala,Leonard E G Mboera,Teun Dekker,Kija Ng’Habi,Rodrigo Silva,Anitha Philbert,Jesse Saroli,Agenor Mafra-Neto,Woodbridge A Foster

doi:10.1186/s12936-020-03395-2

Abstract

BackgroundMosquitoes use odours to find energy resources, blood hosts and oviposition sites. While these odour sources are normally spatio-temporally segregated in a mosquito’s life history, here this study explored to what extent a combination of flower- and human-mimicking synthetic volatiles would attract the malaria vector Anopheles gambiae sensu stricto (s.s.)MethodsIn the laboratory and in large (80 m2) outdoor cages in Tanzania, nulliparous and parous A. gambiae s.s. were offered choices between a blend of human skin volatiles (Skin Lure), a blend of floral volatiles (Vectrax), or a combination thereof. The blends consisted of odours that induce distinct, non-overlapping activation patterns in the olfactory circuitry, in sensory neurons expressing olfactory receptors (ORs) and ionotropic receptors (IRs), respectively. Catches were compared between treatments.ResultsIn the laboratory nulliparous and parous mosquitoes preferred skin odours and combinations thereof over floral odours. However, in semi-field settings nulliparous were significantly more caught with floral odours, whereas no differences were observed for parous females. Combining floral and human volatiles did not augment attractiveness.ConclusionsNulliparous and parous A. gambiae s.s. are attracted to combinations of odours derived from spatio-temporally segregated resources in mosquito life-history (floral and human volatiles). This is favourable as mosquito populations are comprised of individuals whose nutritional and developmental state steer them to diverging odours sources, baits that attract irrespective of mosquito status could enhance overall effectiveness and use in monitoring and control. However, combinations of floral and skin odours did not augment attraction in semi-field settings, in spite of the fact that these blends activate distinct sets of sensory neurons. Instead, mosquito preference appeared to be modulated by blood meal experience from floral to a more generic attraction to odour blends. Results are discussed both from an odour coding, as well as from an application perspective.

Highlights

Mosquitoes use odours to find energy resources, blood hosts and oviposition sites
The positive results achieved through the universal coverage of long-lasting insecticide-treated nets (LLINs) and indoor residual spraying (IRS) have caused the community, policy makers and other malaria control stakeholders to redirect resources toward these interventions and away from other vector control techniques [9]
Laboratory experiments In the laboratory experiment, a total of 292 females were captured in the traps, 157 non-parous and 135 parous out of 480 female mosquitoes that were released during the experiment

Summary

Introduction

Mosquitoes use odours to find energy resources, blood hosts and oviposition sites. While these odour sources are normally spatio-temporally segregated in a mosquito’s life history, here this study explored to what extent a combination of flower- and human-mimicking synthetic volatiles would attract the malaria vector Anopheles gambiae sensu stricto (s.s.) Methods: In the laboratory and in large (80 m2) outdoor cages in Tanzania, nulliparous and parous A. gambiae s.s. were offered choices between a blend of human skin volatiles (Skin Lure), a blend of floral volatiles (Vectrax), or a combination thereof. Several interventions have been reported to play substantial roles in this decline, including improved case management and Kemibala et al Malar J (2020) 19:318 malaria diagnostic methods, as well as the deployment of long-lasting insecticide-treated nets (LLINs) and indoor residual spraying (IRS) to reduce interactions between mosquito vectors and humans [2, 6,7,8]. To complement current interventions and to sustain the gains of universal coverage by LLINs and IRS, further exploration of novel and innovative strategies is of paramount importance

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