A field evaluation of four larval mosquito control methods in urban catch basins.

Effective control of mosquitoes in rural Midwestern communities that lack organized mosquito control districts would be aided by baseline data on optimal breeding sites, interannual effects of climate on population emergence and abundance, and efficacy of various control options under field conditions. During 19 surveillance weeks in the summer of 2005, we sampled 100 catch basins each week that were distributed among 10 study zones. Catch basins within each study zone were subjected to 1 of 4 different mosquito control methods or were left untreated. Of the 10 study zones, 5 were in high-intensity urban areas and 5 in low-intensity urban areas. During the study period, treatment of urban catch basins with Altosid XR extended residual briquets resulted in a 69.5% reduction in mosquito larvae numbers. However, the product did not provide sustained treatment for the 120-150 days suggested by the manufacturer. Vectolex WSP, when applied according to manufacturer's suggestions, resulted in a 73.4% reduction in mosquito larvae. VectolexWSP effectiveness was impacted by heavy rainfalls early in the surveillance period. Cleaning catch basins once or twice during the surveillance period resulted in a 40.1% and a 39.9% reduction in mosquito larvae, respectively. Catch basins in high-intensity urban areas comprised 27.7% of the total collection compared to 72.3% from low-intensity urban areas. The AltosidXR extended residual briquets and the VectolexWSP products both impacted the number of mosquito larvae collected. However, a single treatment to control mosquitoes in this study area may not be sufficient. We suggest that treatment of urban catch basins is optimized when accompanied by a comprehensive surveillance plan, and that a combination of treatments or multiple treatments during the season may be necessary to mitigate risks of vector-borne infectious diseases in areas with similar climate and precipitation trends.