The potential impact on mosquito larvae by threespine stickleback (Gasterosteus aculeatus) and mosquitofish (Gambusia affinis) in four constructed wetlands

Mosquitofish (Gambusia affinis Baird and Girard) and threespine stickleback (Gasterosteus aculeatus) thrive in freshwater marsh habitats, in places where mosquito (Culicidae) larvae occur. This study assessed the potential impacts of mosquitofish (Gambusia affinis) and threespine stickleback (Gasterosteus aculeatus) on mosquito and other macroinvertebrate communities living in constructed wetland Hydrocotyle beds. Littoral macrofauna was collected at 48 sites within Allen, Gearheart, Hauser, and Aldergrove marshes in Arcata, California. Sites were sampled every two weeks from May through September of 2005 for fish and available prey by utilizing minnow traps and a 1 liter dipper. Stomach samples of juvenile and adult threespine stickleback and mosquitofish were compared with abundance and seasonal changes of potential prey to determine monthly diet preferences. Niche overlap value (Cxy (0.33)) demonstrated that little overlap was occurring in diet between both species. In addition, both species were utilizing potential prey items in proportion to their abundance. As mosquito larvae and other prey densities increased, both stickleback and mosquitofish diversified their prey selection to include a variety of prey. However, during this diversification in prey selection, mosquitofish exhibited a Type III feeding response to mosquito larvae, while stickleback showed no clear response to the increase of mosquitoes. This difference in feeding response is likely due to concentration of predator search in the preferred habitat of the prey, palatability, prey vulnerability, and response to other prey items. The lack of predation on mosquito larvae, coupled with periodic consumption of mosquito larvae predators such as Dytiscidae, show stickleback would be inadequate as a biological control agent of mosquitoes in constructed wetlands. Mosquitofish significantly consumed mosquito larvae more than any other prey (p 0.05), and consumed significantly greater numbers of mosquito larvae than stickleback when stomach samples from all marshes were examined. The positively correlated mosquitofish feeding response to increased numbers of mosquito larvae, especially in Allen Marsh, makes this fish a good choice for biological control of mosquitoes in heavily vegetated wetlands.