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Mosquito numbers in 2006

Together with R.J. Beck of the Tippecanoe County Health Department and one intern, 168 visits were made to habitats that supported mosquito larvae or were suspected of supporting them.  Similar to 2005, the rainfall pattern and limited amounts of rain per rainfall event in the Lafayette resulted in relatively few mosquitoes.  Again, in contrast to 2003 and 2004, much of Tippecanoe County experienced no extensive habitats that supported development of larvae of Aedes and Psorophora mosquitoes.  The major watersheds did not flood and rainwater that collected in catch basins and soil depressions dried up before Aedes and Psorophora eggs hatched or larval development was completed. Habitats that supported the development of Culex larvae in 2003 and 2004 tended to remain dry or didn't support larvae throughout most of the summer.

One notable exception was near the town of Stockwell in southeastern Tippecanoe County.  An Indiana State Health Department (ISHD) intern collected over 800 Culex adults per trap night in a gravid trap set up adjacent to the Stockwell sewage treatment plant in late July and early August.  As reported by the ISHD, seven "pools" of these mosquitoes tested positive for West Nile virus.  An attempt was made on August 22 to locate the source(s) of the Culex mosquitoes. The entire residential area of Stockwell and areas adjacent to the sewage plant were surveyed for larval habitats, but no existing site or likely site was found.  Readers interested in the details of our investigation may contact John MacDonald.

There were notable collections of potential mosquito vectors in Tippecanoe County for the first time in 2006.  The first involved a dry ice trap set up in a wooded area in southeast Lafayette in which one female Culex tarsalis was collected on August 24. According to Siverly (1972), this species is infrequently collected in Indiana. Adult C. tarsalis have a prominent white band on the proboscis and prominent white bands on the legs.  Because of these features, specimens of C. tarsalis could be confused with commonly collected Coquillettidia perturbans.  The same trap collected one female Aedes albopictus on September 15 and another female on September 22. Larvae of Aedes japonicus were found at two sites on August 22.  One mature larva was collected from a plastic bucket in a wooded area just east of Stockwell, together with Aedes triseriatus larvae.  Another mature larva of A. japonicus was collected from a small, concrete ornamental pond filled with decaying leaves together with early stage larvae of Orthopodomyia signifera and Culex restuans,plus large numbers of "drain fly" larvae (Diptera; Psychodidae).  The ornamental pond was situated in a shaded residential yard in West Lafayette was drained and cleaned by the homeowners.

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