Mosquito populations in the Powder River basin, Wyoming : a comparison of natural, agricultural and effluent coal bed natural gas aquatic habitats
Doherty, Melissa Kuckler.
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Coal bed natural gas development in northeastern Wyoming has increased surface water in ranching and agricultural areas over undeveloped land. This increase of water increases larval habitat for mosquitoes, potentially increasing adult populations of West Nile virus vector mosquitoes. I compared adult and larval mosquito populations in four different habitat types in the Powder River basin including agricultural, natural, CBNG and upland sagebrush steppe. Adult mosquitoes were sampled weekly (2004) or bi-weekly (2005) using CDC miniature black-light traps baited with dry ice. A fixed-effect mixed model indicated that in a normal rainfall year (2005) mature CBNG ponds had the highest adult mosquito populations of all sites sampled, and the highest population of the WNV vector Culex tarsalis. In a drought year (2004) where total rainfall from May - August was 59% of the seasonal average, agricultural areas had the highest mosquito abundance, likely due to increased irrigation. Adult Culex tarsalis tested positive for WNV across the PRB in 2004 and 2005, with highest minimum infection rates in those areas with large Culex tarsalis populations.Larval mosquitoes were sampled bi-weekly from 13 May - 24 August 2005, using a 350 ml dipper in a 20 point vegetated transect along the pond perimeter. Pond vegetation characteristics were recorded between 3 and 17 August including vegetation density, type and class. Larval Culex tarsalis were the most abundant mosquito in the region, representing 47.7% of the total sampled population. A fixed-effects mixed model found Culex tarsalis produced at similar rates in natural, new, old and outlet CBNG sources; irrigated agriculture produced significantly less (P <or= 0.02) Culex tarsalis in 2005. New and old CBNG ponds and outlets also produced Culex tarsalis over a longer period of time than natural or irrigated agricultural sites. This study indicates that CBNG ponds are significantly increasing the overall population of vector mosquitoes in the PRB, as well as adding to the duration of larval habitats that would normally be ephemeral. Thus CBNG ponds and associated habitats enhance mosquito abundance and may serve to increase pathogen transmission in an otherwise arid ecosystem.