Susceptibility of Field Collected House Flies to Spinosad Before and After a Season of Use

摘要

Spinosad is a new and highly promising insecticide with anovel mode of action, and it was first available for house fly control in theUnited States in 2005. To maintain the effectiveness of this new insecticide, itwill be important to monitor populations for the evolution of resistance.We compared three bioassay methods (topical application, residual exposure,and feeding) using laboratory strains of spinosad susceptible and resistantadult house flies. Topical application was the most reliable and efficientmethod for detection of spinosad-resistant individuals. Using this bioassay weevaluated house flies that were collected before spinosad use (in 2004 and2005). We found significant differences in survival between dairies, suggestingthere was inherent variability between house fly populations prior to spinosaduse. We also evaluated field collected house flies from before and after oneseason of spinosad use (2005). There was no evidence spinosad resistance wasevolving after one season of spraying. Uses and limitations of monitoring spinosad resistance by this method are discussed.