Monitoring Early Season Mosquito and Bird Populations: Implications for West Nile Virus in Lancaster County, Nebraska

West Nile virus (WNV) surveillance e_orts in Nebraska focus on the late summer and early fall months. We studied mosquito and bird populations in Lancaster County, Ne- braska to evaluate the potential for WNV transmission in the late spring and early summer, prior to occurrences of human WNV infections. Culex tarsalis is the most important vec- tor of WNV in Nebraska and was the focal species for the study. Mosquitoes were trapped at six locations representing three habitat types from May 14 to July 11, 2007. The C. tarsalis population, as estimated by the number of individuals caught in the traps each night, peaked early in the study period and then declined. Surveys of avian communities at the sites showed that competent WNV reservoir species were present throughout the study period. We also tested Culex mosquitoes for the presence of WNV. One of 95 pools of Culex mosquitoes tested for WNV using the Rapid Analyte Measurement Platform (RAMP) method returned a positive reading. Modeling the distribution of the RAMP test results indicated that additional pools might have contained mosquitoes with WNV. The high C. tarsalis population observed in the late spring and the WNV-positive pools suggest that studying early season mosquito populations can provide valuable information for evaluating the risk of West Nile virus to humans later in the year.