The effects of mating and blood feeding on the immune defense of female Aedes aegypti mosquitoes

Mating and consequent reproduction have variable effects on the immune defenses of female insects, ranging from immune enhancement to immune suppression. Blood feeding, which is necessary to induce egg production in anautogenous insect species, also impacts immunity, with variable effects in different insect species. Because immunity is a key component of vector competence, and mating and blood feeding can influence immunity, we investigated the effects of these processes on immune defense in the yellow fever mosquito, Aedes aegypti. To explore both aspects of reproduction, we measured survival, bacterial load, and bacterial prevalence in response to mating and blood feeding in adult female Ae. aegypti infected with various doses of the opportunistic bacterial pathogen, Serratia marcescens. When we challenged females with a high dose of S. marcescens, we found that mating induced significantly higher survival probabilities and bacterial loads in non-blood fed individuals. Mating improved survival after infection with a moderate dose of S. marcescens as well, but when we challenged females with a low dose, we observed no effect of mating on survival or bacterial load. Thus, the effects of mating on immune defense appear to be dose dependent. Blood feeding, on the other hand, consistently reduced survival regardless of dose. By exploring how key life history traits impact immune defense, our results continue to advance a thorough understanding of how Ae. aegypti defend against infection.