Crowding effects in the yellow fever mosquito (Aedes aegypti) and its impact on insecticide sensitivity

Aedes aegypti is a globally important mosquito species because it is a principle vector of dengue, yellow fever, and chikungunya. In order to better control A. aegypti populations it’s necessary to thoroughly understand its ecology, life history traits and response to control methods (primarily insecticides). Larval density is important because it has strong effects on survival and future fitness. Density effects can result from resource competition or crowding, the latter of which has received less research attention despite its ecological importance. Both physical and chemical components cause crowding interactions in larval mosquitoes, which result in increased mortality, prolonged development, and reduced size.

The objectives of this research were to determine how different crowding conditions affect insecticide sensitivity. I hypothesized that stress due to crowding would increase insecticide sensitivity and that a specific density can be determined where the combined effect becomes biologically significant. Preliminary results indicate that when larvae are reared at various crowding densities (without resource competition) but later exposed to insecticide at equal densities they exhibit similar sensitivity. However, when larvae were reared at equal densities but exposed at various crowding densities there appears to be a protective effect of crowding, as more densely crowded larvae were significantly less sensitive.These results are somewhat counterintuitive and future efforts will determine underlying mechanisms of observed effects. This research provides important insights into how mosquitoes may respond to control efforts as well as providing empirical recommendations on designing laboratory toxicity tests to better reflect ecological conditions in natural mosquito populations.