Effect of marsh design on the abundance of mosquitoes in experimental constructed wetlands in southern California.

The species composition and abundance of larval mosquitoes were studied in the vegetated regions of 2 types of experimental constructed wetlands: one-phase marshes, which have continuous vegetation throughout the marsh, and 3-phase marshes, which have 2 vegetated regions separated by a region of comparatively deeper open water. Larvae of Culex spp. were significantly more abundant in one-phase marshes than in 3-phase marshes. Larval populations in one-phase marshes also contained proportionately more older larval instars (stages III and IV) than did populations in 3-phase marshes. Mortality rates of larvae increased during the summer and were higher in 3-phase marshes than in one-phase marshes during the initial 6 wk of the study. Differences in mortality rates between marsh types were related to predator abundance during the first 6 wk of the study and thereafter were not strongly associated with predator populations. An infusion of decaying bulrush (Schoenoplectus californicus) stimulated oviposition by gravid Culex stigmatosoma more than by gravid Culex quinquefasciatus and Culex tarsalis. Culex erythrothorax was the most abundant host-seeking species collected in CO2-baited traps; however, larvae were rarely collected during routine dip sampling and egg rafts were never collected in oviposition studies.