Increased arbovirus transmission risk from interactions between competition and pesticide exposure in larval mosquitoes

Larval mosquitoes occupying container and ephemeral habitats often experience high competitive stress, reducing the number of subsequent adults and affecting their physiology.   Mosquito control often includes application of pesticides to larval habitats, altering the number of larvae present and thus modifying competition.  The vectorial capacity of the adult population for arboviruses such as dengue virus is a function of the population size and the physiology of the individual adults, affecting survival, susceptibility and biting rate.  Thus, the risk of arbovirus transmission may be a complex function of competition and pesticide exposure experienced in the larval environment.  We explored these interactions using a modified vectorial capacity model, varying relationships and parameter values linking pesticide exposure and competition to adult population size, daily survival probability, susceptibility to infection and biting rate.  Under most conditions examined, there were regions of parameter space where increasing pesticide increased the transmission risk from the adult population.  This was driven partly by competitive release, with more adults emerging from high competition containers when treated with pesticide than when untreated due to the relaxation of competition.  However, when competitive release was not included there were still regions of parameter space where pesticide exposure increased arbovirus transmission risk.  Further work is needed to determine the likelihood of this occurring in the field and to develop control strategies that minimize this effect.