ARS | Publication request: Selection for Resistance to Imidacloprid in the House Fly (Diptera: Muscidae)

Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 30, 2010
Publication Date: January 15, 2011
Citation: Kaufman, P.E., Nunez, S.C., Geden, C.J., Scharf, M.E. 2011. Selection for Resistance to Imidacloprid in the House Fly (Diptera: Muscidae). Journal of Economic Entomology. 103(5):1937-1942. DOI: 01.1603/EC10165

Interpretive Summary: House flies continue to be major pests of livestock, poultry and humans throughout the world. Fly control is a difficult matter in part because of the rapidity with which house flies have developed resistance to insecticides that are used to control them. In recent years several new insecticides with novel modes of action have been introduced for fly control, yet some farmers have reported that these novel products are already showing decreased potency in the field. In a previous study it was documented that house flies are indeed showing early signs of resistance to imidacloprid, the most commonly used of these “new” insecticides for fly control. The purpose of this study, conducted by scientists at the University of Florida and ARS’s Center for Medical, Agricultural and Veterinary Entomology (Gainesville, Florida), was to document the rapidity with which house flies can become resistant to imidacloprid. After five generations of moderate selection, a colony of house flies established from field collections displayed resistance levels that were over 300X higher than in unselected flies from the same colony. These resistant flies showed substantial tolerance to QuickBayt, a commercial formulation of this insecticide that is widely used by farmers. The results demonstrate that there is an urgent need to rotate use of imidacloprid with other management methods in order to prevent resistance from reaching levels that would result in the collapse of fly-control efforts in the field.

Technical Abstract: House flies, Musca domestica L., continue 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 a house fly strain, FDm was created by a 20% contribution from each of five colonies collected from dairies in Florida with known imidacloprid resistance. The FDm strain was used to evaluate the level of imidacloprid resistance following five 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 following its creation, as compared to the five parental strains. Between 9,500 and 14,000 virgin house flies were used in each selection. Following the fifth and final selection, a 331-fold increase in imidacloprid resistance at the LC70 was observed over the parental FDm strain. In parallel studies, the FDm strain showed increasing tolerance of the commercial imidacloprid product, QuickBayt. These results suggest that livestock producers should use caution when choosing pesticides and consider rotating fly baits, as is encouraged with other pesticide treatment regimes on farms.