Two species of Culex mosquitoes are common throughout much of North America. Culex restuans Theobold is a native species, whereas Culex pipiens L. is a European immigrant that has been in North America since the 1600s. Larvae of Cx. restuans are numerically dominant in spring and early summer but Cx. pipiens dominates by mid-summer. This transition is termed the "Culex crossover" and has been previously explored in larval populations, largely because Cx. pipiens is more likely to transfer West Nile virus to humans. Adult mosquitoes of both species were captured in 14 light traps in Lucas County, OH, between May and October 1980-2011. We examined this 31-yr, continuous record of adult populations for signs of a species crossover, relationships between abundances of both species and climate factors, and evidence of interspecific competition. The total cumulative degree-days (above 0°C), total cumulative precipitation, and total number of each species were calculated for each day of January-September (annual) and May-September (mosquito season) of each year. On average, adult Cx. pipiens became numerically dominant over Cx. restuans on day 175 ± 21 (June 24), consistent with the Culex crossover reported for their larvae. Pearson correlations showed that abundances of both species were related to temperature and precipitation, but Cx. pipiens tended to be positively related to climatic factors, whereas Cx. restuans showed negative correlations. Moreover, abundances of the two species were more positively than negatively related to one another, providing no evidence of interspecific competition.
Keywords: Culex crossover; Culex pipiens; Culex restuans; competition; mosquito.
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