Spatial variation in food supply, mating behavior, and sexually transmitted disease epidemics

Mating behavior helps to shape the epidemiology of sexually transmitted infections (STIs) by determining the rate at which infectious and susceptible individuals make contact. To the extent that mating behavior shows spatial variation, it is expected that STI epidemics will also show spatial heterogeneity (provided that dispersal is limited). However, empirical data are lacking for natural systems. Here, therefore, we investigate the association between local mating behavior and STI epidemiology in natural populations of the two-spot ladybird, Adalia bipunctata, and dissect the causes of this variation. Variation in mating behavior was observed over local and regional spatial scales and high mating rate led to stronger local epidemics of the STI. Initial ecological observations suggested that reduced mating rate was associated largely with low food supply (and possibly to a lesser extent with local population density) and not with differences in thermal environment. We tested the potential role of food supply in fuelling STI epidemics in laboratory populations and confirmed that high food provision led to greater STI transmission. We conclude that food supply is strongly associated with mating rate in the field and that this produces heterogeneity in STI epidemiology. A consequence is that STI-induced sterility will reduce reproduction in habitat patches of high food quality.