Comparative studies on the melanization response of male and female mosquitoes against microfilariae

The melanization response of adult male and female Aedes trivittatus and the black-eyed Liverpool strain of Aedes aegypti against intrathoracically inoculated Dirofilaria immitis microfilariae (mff) was assessed at 1, 3, and 5 days postinoculation (PI). The melanization reaction of males is significantly less effective than the response elicited by female mosquitoes. No mff in male A. aegypti and only 17% of mff recovered from A. trivittatus were fully melanized by day 5 PI compared with 80% and 100% complete melanization of recovered mff from A. aegypti and A. trivittatus females, respectively. A significantly greater percentage of mff retained their viability in males, and inoculation of heat-killed mff did not significantly increase the melanization response as compared with female mosquitoes. Males have significantly lower total hemocyte populations and hemolymph volumes than females, and the possible relationship of hemocyte numbers and reduced melanization capabilities in males is discussed.