ECOLOGY OF CULEX-TARSALIS (DIPTERA, CULICIDAE) - FACTORS INFLUENCING LARVAL ABUNDANCE IN MESOCOSMS IN SOUTHERN-CALIFORNIA

Colonization and succession of mosquitoes and macroinvertebrate predators were studied in 30-m2 ponds (mesocosms) during summer and fall 1987. Larval abundance of Cx. tarsalis Coquillette was lower during the hot, summer months than during the fall. In all studies, larval populations declined markedly 2-3 wk after habitat flooding. Although predator abundances differed in these studies, sometimes by an order of magnitude, the common predators colonized mesocosms in the following order: Triops, hydrophilid beetle larvae, dytiscid beetle larvae, mesoveliids, dragonfly and damselfly naiads, and notonectids. The similarity of the colonization phenologies probably resulted from the vagility of the adult insects and species-specific developmental rates. Stepwise multiple regression was used to identify factors potentially affecting larval mosquito populations. For most studies, coleopteran larvae were related inversely to per capita change in the entire larval population and the third- and fourth-instar subpopulation (i.e., large coleopteran larval populations were associated with large declines in the Cx. trasalis larval population). Maximum water temperatures and pond age (days after flooding) also were identified as significant factors affecting larval abundance and per capita change of mosquitoes. Potentially lethal water temperatures (greater than or equal to 35 degrees C) occurred during the summer; however, the declines in larval abundance of Cx. tarsalis were not restricted to (or obviously associated with) periods of high water temperature. Our results indicated that predation by coleopteran larvae and factor(s) associated with pond age, such as mosquito ovipositional preferences, significantly affected Cx. tarsalis larval populations.