Host choice by mosquitoes is a critical component in the transmission of mosquito borne viruses.  Birds are important hosts for mosquitoes and crucial reservoirs for many encephalitis viruses.  Several virus vectors have been shown to switch from feeding on birds in spring and early summer to mammals in late summer and fall. This shift drives the timing of encephalitis epidemics in humans.  The factors that drive the host shift in mosquitoes, however, remain unclear.  One prominent hypothesis proposes that birds migrating into and out of habitats cause fluctuations in the proportions of available bird and mammal hosts.  Another prominent hypothesis maintains that young-of-the-year birds are preferred hosts for mosquitoes and that young-of-the-year are a major component of mosquito blood meals in spring and early summer.  After young-of-the-year fledge, mosquitoes switch to feeding upon mammals in the absence of their preferred host.  We sought to test a modified version of this hypothesis by examining the relationship of mosquitoes, birds and frogs at a study site in Alabama, using a seven year data set generated at this site.  We broaden the scope of the latter hypothesis to include other aspects of host biology, such as mate attraction, brooding/nesting, and territory defense.  We sought to test whether or not mosquitoes target hosts that are actively attracting mates, recently recruited and/or rearing young. Host use was determined by PCR-identification of source of blood in guts of field-collected mosquitoes.  

Results/Conclusions

Host use by mosquitoes varied temporally within years among host species.  More importantly, the host use for each species showed remarkable temporal consistency from year to year.  In addition, generalist mosquitoes (those which fed from all host classes) fed on host species that were in their breeding season, while specialist mosquitoes (which fed predominantly within a single host class) did not. For example, Culex peccator, a generalist mosquito that fed on bullfrogs, did so during the period when males were calling, whereas Culex territans, a mosquito that specializes on frogs, fed on bullfrogs during other parts of the year.  Our findings suggest that seasonal patterns of host use by generalist mosquitoes are reflect the reproductive biology of host animals.   Generalist mosquitoes are important bridge vectors, infecting humans and other susceptible mammalian hosts after acquiring virus from avian reservoirs.  These results contribute to our understanding of the biological factors which underlie seasonal patterns of host use which, in turn, drive epidemics of human disease.