VETERINARY ENTOMOLOGY Selection for Resistance to Imidacloprid in the House Fly (Diptera: Muscidae)

The house ßy,Musca domestica L. (Diptera: Muscidae), continues to be a primary pest of livestock facilities worldwide. This pest also has shown a propensity for pesticide resistance development when under high selection pressures. In this study the house ßy strain FDmwas created by a 20% contribution from each of Þve colonies collected from dairies in Florida with known imidacloprid resistance. TheFDmstrainwas used to evaluate the level of imidacloprid resistance after Þve selections near the LC70 value of each selected generation. Overall, the mean selection mortality was 72.7, with males being considerably more susceptible than females. The unselected (F0) FDm strain showed considerable susceptibility to imidacloprid after its creation, compared with the Þve parental strains. Between 9,500 and 14,000 virgin house ßieswere used in each selection. After the Þfth and Þnal selection, a 331-fold increase in imidacloprid resistance at the LC70 was observed over the parentalFDmstrain. Inparallel studies, theFDmstrain showed increasing toleranceof thecommercial imidacloprid product QuickBayt. These results suggest that livestock producers should use caution when choosing pesticides and consider rotating ßy baits, as is encouraged with other pesticide treatment regimes on farms.