Blood-Feeding Success of the Mosquito Aedes aegypti Depends on the Transmission Route of Its Parasite Edhazardia aedis

Abstract

We examined the effect of the microsporidian parasite Edhazardia aedis on the blood-feeding success of its host, the yellow fever mosquito Aedes aegypti. To do so, we exposed mosquito larvae to parasite spores at four intensities and three ages. The amount of blood obtained by adult female mosquitoes increased with increasing age at exposure and with decreasing intensity of exposure. These associations were only partly explained by the direct effects of the parasite on blood-feeding behaviour. Much of the associations were due to the parasite causing indirect effects to the mosquito because of correlations among its life history traits. The parasite increased age at pupation and decreased wing length, both of which were associated with the size of blood meals. Thus, trade-offs implicit in the host's life history - the correlations between wing length, age at pupation and blood meal size - were crucial in determining the parasite's effect on the host's blood-feeding success. E. aedis has two types of spores, a uninucleate spore used for horizontal transmission and a binucleate spore used for vertical transmission. This allowed us to investigate the influence of different transmission routes on the host's blood-feeding behaviour. While blood-feeding success decreased as the number of uninucleate spores increased, it was not influenced by the number of binucleate spores. Thus the parasite decreases its impact on the host, i.e. its virulence, during the part of the life cycle when transmission is vertical.