Diving beetles (Dytiscidae) as predators of mosquito larvae (Culicidae) in field experiments and in laboratory tests of prey preference.

Field experiments were performed in artificial ponds to evaluate how the density of predatory diving beetles (Dytiscidae) would affect the population levels of mosquito larvae (Culicidae). Mosquitoes colonizing the ponds were predominantly species of the genus Culex. In 2000, most of the dytiscids colonizing the ponds were small (Hydroporus spp.), and these predators had no impact on the size of larval mosquito populations, not even in ponds with added dytiscids. In 2001, larger beetles (Ilybius, Rhantus, and Agabus spp.) were more common, and there were significantly fewer mosquito larvae in ponds with the highest numbers of dytiscids. There was a negative correlation between numbers of diving beetles in the ponds and the mean body length of mosquito larvae. In neither year could dytiscid densities be maintained above a certain level owing to emigration. In laboratory tests, there were marked differences between three common dytiscid species in regard to preferences for Daphnia and Culex species as prey: Colymbetes paykulli Erichson chose mosquito larvae more often, whereas both Ilybius ater (De Geer) and I. fuliginosus (Fabricius) preferred Daphnia spp. All of the tested dytiscids consumed large numbers of prey. Since some dytiscid species can efficiently decrease populations of mosquito larvae, they are probably important in the natural control of these dipterans.