MOSQUITO SPECIES COMPOSITION AND ITS IMPLICATIONS FOR DISEASE TRANSMISSION IN AN IOWA WETLAND

  Sara L. Sheeley, Matthew J. Hjortshoj, Bradley H. Hess, Jonathan M. Eastman, Edward J. Brown and David R. Mercer 

   Mosquitoes serve as vectors in many disease cycles.  Because some mosquito species are better vectors for certain illnesses than others, we must understand the species composition in an area to assess the risk of disease transmission.  Beaver Creek Wetlands (Black Hawk County, IA) was surveyed from May 3 to July 24, 2002.  Factors that may influence mosquito development, including water pH, temperature, electrical conductivity, total alkalinity, depth, turbidity, and dissolved oxygen, were measured at 6-24 sites each week.  Percentage and type of plant cover, amount of detritus, other invertebrates, and concentrations of nitrate, nitrite, phosphate, and bacteria were also estimated.  Mosquito larvae sampled were raised to adulthood and identified.  A correlation matrix suggested few relationships between factors measured and mosquito production.  A scale of relative risk of mosquito-borne disease was created for the sites sampled based on the numbers of mosquitoes at each sample site and their published vector capabilities.

   Although the wetlands produced relatively few mosquitoes during our survey, many of the species represented in the samples are competent vectors for illnesses such as Western and Eastern Equine Encephalitis, St. Louis Encephalitis, and West Nile Virus.  The most common mosquitoes found were Aedes vexans and Culex tarsalis.  Less common vector species were Uranotaenia sapphirina and Culex salinarius.  The majority of vector species were found in temporary pools, which dried and refilled throughout the survey.  Larger, more permanent water bodies and channels produced far fewer mosquitoes, and therefore, fewer competent vectors.  Open water did not produce mosquitoes. 

   Although many significant correlations were found among putative developmental factors, none of the factors measured correlated significantly with total mosquito production.  Anopheline mosquitoes correlated significantly with alkalinity and bacteria, but very few anopheline mosquitoes were found.  Wetlands provide numerous ecological benefits, but apparently do not represent a high mosquito-borne disease risk.

We are very grateful for the support provided by the Roy J. Carver Charitable Trust, the Iowa Space Grant Consortium, and the Department of Biology, University of Northern Iowa.