Resistance of the little house fly to insecticides on poultry facilities

F i l t h fly control on poultry facilities in California is not limited to the house fly but also includes the little house fly. In fact, the little house fly, Fannia canicularis (L.), is of greater economic importance to poultry producers than the house fly, Musca domestica L., mainly because it occurs during the cool and wet season, when standard manure-drying practices are not always reliable control options. With California’s population growth of the past 20 years, urban and suburban communities have extended into areas previously dedicated to poultry production. Since the little house fly readily coexists with humans, it is not surprising that complaints by residents to public health officials have increased with the population growth. During a seven-year period, the greatest proportion of legal notices filed in connection with infestations of various fly species in Riverside County occurred during the peak of the little house fly season (fig. 1). To meet the need for more immediate and effective control of little house fly, poultry producers have relied heavily on the use of insecticides, thus setting the stage for development of insecticide resistance. The pyrethroid permethrin has become the predominant insecticide for filth fly control on poultry facilities in recent years. Before pyrethroids were commercially available for fly control, they were found to be nearly as toxic to field-collected, organophosphate-resistant house flies as to susceptible house flies. Since their introduction for fly control on livestock and poultry facilities in the late 1970s, several cases of house fly resistance to pyrethroids have been reported, implying that the same problems might be developing in the little house fly populations. In light of the 17-year time span since the last published survey of little house fly resistance to insecticides in California, and the advent of pyrethroids as a completely new class of commercially available insecticides, we conducted a study to determine the current status of resistance of this species in various areas of the state. Our results suggested that, although resistance was higher for permethrin than for the other insecticides tested, levels were not excessive at any of the sites.