Assessment of resistance risk to fipronil and cross resistance to other insecticides in the Musca domestica L. (Diptera: Muscidae).

Fipronil, a phenyl-pyrazole insecticide has been used frequently for the control of disease vector house flies, Musca domestica L., (Diptera: Muscidae) worldwide including Pakistan. This experiment was performed to determine the selection and assessment of fipronil resistance evolution along with cross resistance to other three insecticides. After 26 generations of selection, the house fly strain developed 430-fold resistance to fipronil compared to a susceptible strain. Realized heritability (h(2)) of resistance to fipronil was 0.05. The projected rate of resistance development revealed that if 30-90% house flies were selected then a tenfold increase in lethal concentration 50 happened after 95.51-26.59 generations for fipronil (h(2)=0.05, Slope=2.34). At similar slope, if h(2)=0.15, then 31.84-8.86 generations are required for tenfold increase in LC50 at 30-90% selection intensity, respectively. Likewise, if h(2)=0.25, then similar would occur in 19.10-5.32 generations. Differences in any of the variable would affect the rate of resistance development. Selection with fipronil did not increase the level of resistance to lambda-cyhalothrin, profenofos and indoxacarb, suggesting no cross resistance to these insecticides. The results of our study concluded that house flies have the potential to develop resistances following continued selection pressure with fipronil.