The abundance and seasonal distribution of Culex mosquitoes in Iowa during 1995-97

The abundance and seasonal distribution of Culex mosquitoes were monitored by measuring oviposition activity during the summers of 1995, 1996, and 1997. Five species of culicine mosquitoes laid egg rafts in ovitraps. Egg rafts of 4 Culex species - Cx. restuans (54.98%), Cx. pipiens (25.41%), Cx. salinarius (12.18%), and Cx. tarsalis (0.14%) - constituted more than 92% of the total egg rafts collected. Culiseta inornata (0.1%) was the only other species to lay viable egg rafts in the ovitraps. A small percentage (7.19%) of egg rafts did not hatch; thus identification was not possible. Compared with New Jersey light trap data in a nearby area, the abundance of Cx. tarsalis and Cs. inornata was markedly underestimated with ovitraps. These data may also reflect differences in the specific location of the 2 trap sites rather than attractiveness of ovitraps for Cx. tarsalis and Cs. inornata. In general, Cx. restuans oviposition activity began in late May, and it was the dominant Culex species through June. After July 1, the number of egg rafts laid by Cx. restuans decreased continually until the end of the summer. Culex pipiens and Cx. salinarius oviposition began in early June and increased gradually during the summer. Over the course of a summer, there were about twice as many Cx. pipiens as there were Cx. salinarius. A crossover in the number of Cx. pipiens and Cx. restuans egg rafts occurred in late July or early August, depending on the year. By late August each year, Cx. pipiens was the most abundant species. At this time, Cx. restuans and Cx. salinarius populations were similar, but each was about half of the Cx. pipiens population. Differences in the abundance of all 3 species could not be explained by changes in ambient temperature (both minimum and maximum) or relative humidity, either within or among years.