State-dependent domicile leaving rates in Anopheles gambiae

Simon P W Zappia,Alex M Chubaty,Bernard D Roitberg

doi:10.1186/s12936-017-2166-4

Abstract

BackgroundTransmission of Plasmodium greatly depends on the foraging behaviour of its mosquito vector (Anopheles spp.). The accessibility of blood hosts and availability of plant sugar (i.e., nectar) sources, together with mosquito energy state, have been shown to modulate blood feeding (and thus biting rates) of anopheline mosquitoes. In this study, the influence of mosquito starvation status and availability of nectar on the decision of female Anopheles gambiae mosquitoes to leave a bed net-protected blood host was examined.MethodsTwo small-scale mesocosm experiments were conducted using female mosquitoes starved for 0, 24 or 48 h, that were released inside a specially constructed hut with mesh-sealed exits and containing a bed net-protected human volunteer. Floral cues were positioned on one side of the hut or the other. Several biologically plausible exponential decay models were developed that characterized the emigration rates of mosquitoes from the huts. These varied from simple random loss to leaving rates dependent upon energy state and time. These model fits were evaluated by examining their fitted parameter estimates and comparing Akaike information criterion.ResultsStarved mosquitoes left domiciles at a higher rate than recently fed individuals however, there was no difference between 1- and 2-day-starved mosquitoes. There was also no effect of floral cue placement. The best fitting emigration model was one based on both mosquito energy state and time whereas the worst fitting model was one based on the assumption of constant leaving rates, independent of time and energy state.ConclusionsThe results confirm that mosquito-leaving behaviour is energy-state dependent, and provide some of the first evidence of state-dependent domicile emigration in An. gambiae, which may play a role in malarial transmission dynamics. Employment of simple, first-principle, mechanistic models can be very useful to our understanding of why and how mosquitoes leave domiciles.

Highlights

Transmission of Plasmodium greatly depends on the foraging behaviour of its mosquito vector (Anopheles spp.)
There was no effect of experiment end time on the proportion of mosquitoes leaving the hut across the three starvation treatments (p = 0.1; see Additional file 1)
The authors end by referring back to their attempt to view the results through the lens of simple, underlying mechanisms. Such approaches may provide great utility to help sift through various explanations for outcomes in complex environments. These experiments provide some of the first evidence for state-dependent domicile emigration in An. gambiae

Summary

Introduction

Transmission of Plasmodium greatly depends on the foraging behaviour of its mosquito vector (Anopheles spp.). The accessibility of blood hosts and availability of plant sugar (i.e., nectar) sources, together with mosquito energy state, have been shown to modulate blood feeding (and biting rates) of anopheline mosquitoes. The influence of mosquito starvation status and availability of nectar on the decision of female Anopheles gambiae mosquitoes to leave a bed net-protected blood host was examined. Malaria dynamics may depend greatly on the distribution of hosts, vectors, the ease of movement between human habitations (where Anopheles mosquitoes forage for blood), and on the availability and distribution of plant sugars (i.e., nectars) [1, 2]. It is recognized that sugar (generally nectar) is critical to survival of Anopheles mosquitoes in nature, for both males and females [e.g., 5]. Many of these nectar sources are located outside of domiciles, as noted above, sugar sources may Zappia et al Malar J (2018) 17:25 impact the distribution of resource-seeking mosquitoes in space and time

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