The midgut bacterial flora of wild Aedes triseriatus, Culex pipiens, and Psorophora columbiae mosquitoes.

The midgut bacterial flora of wild-caught Aedes triseriatus, Culex pipiens, and Psorophora columbiae mosquitoes was investigated. Dissected midgut contents were examined using quantitative aerobic bacterial cultures. Individual colonies (n = 134) were subcultured and identified to species. Midgut bacterial counts changed dramatically during mosquito development. A 280-1,100-fold decrease in the bacterial population occurred between the larval stage and pupal emergence, whereas a subsequent 70-16,000-fold increase occurred after blood-feeding. Bacterial identifications revealed a complex flora with up to nine genera identified during any stage of development. Species most frequently isolated were Serratia marcescens, Klebsiella ozonae, Pseudomonas aeruginosa, and Enterobacter agglomerans. The presence of genetically well-characterized bacteria in the midgut flora of mosquitoes may provide a means of expressing novel genetic products in vector species.