Abstract
Females of all blood-feeding arthropod vectors must find and feed on a host in order to produce offspring. For tsetse—vectors of the trypanosomes that cause human and animal African trypanosomiasis—the problem is more extreme, since both sexes feed solely on blood. Host location is thus essential both for survival and reproduction. Host population density should therefore be an important driver of population dynamics for haematophagous insects, and particularly for tsetse, but the role of host density is poorly understood. We investigate the issue using data on changes in numbers of tsetse (Glossina morsitans morsitans Westwood) caught during a host elimination experiment in Zimbabwe in the 1960s. During the experiment, numbers of flies caught declined by 95%. We aimed to assess whether models including starvation-dependent mortality could explain observed changes in tsetse numbers as host density declined. An ordinary differential equation model, including starvation-dependent mortality, captured the initial dynamics of the observed tsetse population. However, whereas small numbers of tsetse were caught throughout the host elimination exercise, the modelled population went extinct. Results of a spatially explicit agent-based model suggest that this discrepancy could be explained by immigration of tsetse into the experimental plot. Variation in host density, as a result of natural and anthropogenic factors, may influence tsetse population dynamics in space and time. This has implications for Trypanosoma brucei rhodesiense transmission. Increased tsetse mortality as a consequence of low host density may decrease trypanosome transmission, but hungrier flies may be more inclined to bite humans, thereby increasing the risk of transmission to humans. Our model provides a way of exploring the role of host density on tsetse population dynamics and could be incorporated into models of trypanosome transmission dynamics to better understand how spatio-temporal variation in host density impacts trypanosome prevalence in mammalian hosts.
Highlights
For any blood-feeding arthropod vector, the process of finding and feeding on a host is essential for reproduction
Tsetse flies are the vectors of human and animal African trypanosomiasis
We develop models including starvation-dependent mortality to explain changes in numbers of the savannah tsetse Glossina morsitans morsitans caught during a host elimination experiment in Zimbabwe in the 1960s
Summary
For any blood-feeding arthropod vector, the process of finding and feeding on a host is essential for reproduction. It has been variously proposed that: (i) tsetse feed opportunistically [6]; (ii) feeding rates increase linearly or exponentially following each meal [5]; (iii) there is a fixed non-feeding period of about three days after each meal followed by intense activity leading to feeding within 0.3–0.8 days [7,8]. These ideas have not incorporated the impact of host density on the probability of feeding
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