Oviposition behavior and larval ecology of <italic>Culex</italic> mosquitoes in southeast Michigan.

Abstract

The patterns of vector borne infectious disease abundance have generally been attributed to patterns of vector abundance. In the case of diseases carried by mosquitoes, adult abundance has been correlated most often with some measure of larval habitat abundance. However, the ecological processes that lead from increased larval habitat to adult abundance have not been well developed. In this dissertation, I examine two major mechanisms that help understand this connection: alleviation of density-dependent reductions in growth and survival at the larval stage, and increased adult survival via optimal oviposition strategies or avoidance of predation. I focus on the principal vectors of West Nile virus in the northern United States: <italic>Culex restuans</italic> and <italic>Cx. pipiens</italic>. When more larval habitat was provided, <italic>Culex restuans</italic> had a lower egg-clutch density, suggesting the potential alleviation of density dependent reductions in growth and survival. In addition, the oviposition pattern demonstrated that females avoided habitats containing conspecific larvae. Furthermore, in laboratory experiments, there was a significant decrease in growth and survival as a function of density (by manipulating volume) and nutrient concentration. In interspecific competition studies, <italic>Culex restuans</italic> demonstrated marginally higher growth and survival than <italic> Cx. pipiens</italic>, although for both species it appeared that intraspecific competition was stronger than interspecific competition. Experiments examining the oviposition behavior of individual female mosquitoes showed little support for oviposition favoring offspring survival, perhaps suggesting the importance of adult survival. Finally, predator enclosure experiments with Long-Eared Northern Bats (<italic>Myotis septentrionalis</italic>) showed a significant reduction in oviposition, likely due to the direct effect of bats depredating egg-laying female mosquitoes. Although I demonstrated the potential importance of density dependence in both field and laboratory studies, these mosquitoes are known to aggregate egg-clutches. In addition, examining the individual behavior experiments and the predation experiments suggests the importance of adult survival, a factor I was unable to measure directly. Understanding the importance of adult survival may have a double impact by explaining both patterns of mosquito abundance, and, more importantly, patterns of vector-borne disease abundance.