Insecticide resistance in house flies from the United States: Resistance levels and frequency of pyrethroid resistance alleles

• Levels of resistance to six insecticides varies between states in the USA.
• Resistance to permethrin was high and found at similar levels at most sites.
• The frequency of Vssc resistance alleles varied between sites.
• The frequency of CYP6D1v1 was relatively consistent between sites.
• The kdr-his allele provides less resistance than kdr or super-kdr.

Although insecticide resistance is a widespread problem for most insect pests, frequently the assessment of resistance occurs over a limited geographic range. Herein, we report the first widespread survey of insecticide resistance in the USA ever undertaken for the house fly, Musca domestica, a major pest in animal production facilities. The levels of resistance to six different insecticides were determined (using discriminating concentration bioassays) in 10 collections of house flies from dairies in nine different states. In addition, the frequencies of Vssc and CYP6D1 alleles that confer resistance to pyrethroid insecticides were determined for each fly population. Levels of resistance to the six insecticides varied among states and insecticides. Resistance to permethrin was highest overall and most consistent across the states. Resistance to methomyl was relatively consistent, with 65–91% survival in nine of the ten collections. In contrast, resistance to cyfluthrin and pyrethrins + piperonyl butoxide varied considerably (2.9–76% survival). Resistance to imidacloprid was overall modest and showed no signs of increasing relative to collections made in 2004, despite increasing use of this insecticide. The frequency of Vssc alleles that confer pyrethroid resistance was variable between locations. The highest frequencies of kdr, kdr-his and super-kdr were found in Minnesota, North Carolina and Kansas, respectively. In contrast, the New Mexico population had the highest frequency (0.67) of the susceptible allele. The implications of these results to resistance management and to the understanding of the evolution of insecticide resistance are discussed.

Frequencies of Vssc alleles in house flies collected from nine states across the USA. Vssc alleles are susceptible (white), kdr-his (speckled), kdr (cross-hatched) and super-kdr (black).Figure optionsDownload as PowerPoint slide