BACTERIAL ENRICHMENT IN THE SURFACE MICROLAYER OF AN ANOPHELES-QUADRIMACULATUS (DIPTERA, CULICIDAE) LARVAL HABITAT

Sampling of the surface microlayer of water in a marsh habitat of Anop heles quadrimaculatus Say in Michigan revealed it to be enriched with bacteria compared with subsurface water samples. Concentrations of tot al numbers of bacteria ranged from 18.8 x 10(6)/ml to 65.4 x 10(6)/ml (mean, 35.9 x 10(6)/ml; n = 13) in surface microlayer samples, and fro m 3.8 x 10(6)/ml to 14.3 x 10(6)/ml (mean, 7.8 x 10(6)/ml; n = 13) in subsurface samples. Specifically, the surface microlayer had higher co ncentrations of three morphotypes of bacteria (cocci, rods, and rods a ttached to detritus particles). Given that bacteria are an important f ood of mosquito larvae, we suggest that the interfacial feeding behavi or of An. quadrimaculatus larvae allows them to exploit the surface mi crolayer, a food-rich zone.