Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/14/2003
Publication Date: 8/1/2003
Citation: LI, A.Y., DENNEHY, T.J., NICHOLS, R.L. BASELINE SUSCEPTIBILITY AND DEVELOPMENT OF RESISTANCE TO PYRIPROXFEN IN BEMISIA ARGENTIFOLII (HOMOPTERA: ALEYRODIDAE) IN ARIZONA. JOURNAL OF ECONOMIC ENTOMOLOGY. 2003. v. 96. p. 1307-1314. Interpretive Summary: The silverleaf whitefly causes millions of dollars in damages to cotton and vegetable crops each year in the desert growing areas of Arizona during the past ten years. The successful control of this pest relies on the availability of efficacious insecticides. Resistance to various traditional insecticides led to widespread control failures, and severe economic losses occurred to Arizona cotton growers in the early parts of 1990s. A novel insecticide, pyriproxyfen, which inhibits development of whitefly eggs was registered in 1996 for whitefly control in Arizona. In order to develop new strategies to reduce the risk of resistance to this important insecticide, a study was initiated in 1996 to determine the baseline susceptibility of whiteflies and to monitor development of resistance in the following years. Whitefly samples were collected each year from cotton fields throughout Arizona, and in 1999 samples were also collected from melon fields and greenhouses. Laboratory bioassays were conducted to test susceptibility of whitefly eggs to different concentrations of this insecticide. No resistance was observed during the first three years of use. In 1999, resistance was found for the first time in whiteflies from cotton, fall melons as well as from greenhouses. The results provide early warning to the emerging problem of resistance to this pivotal insecticide in the desert cropping systems of Arizona. As a result of this study, new control strategies are being developed in order to preserve the effectiveness of this insecticide.
Technical Abstract: Pyriproxyfen (Knack®) was registered in Arizona cotton, as the crucial component of a resistance management plan, to control whitefly Bemisia argentifolii (Bellows & Perring) in 1996. A statewide monitoring program was implemented at the same time to detect and monitor whitefly resistance to this novel insecticide. Bioassays involving dipping of leaves infested with whitefly eggs showed that all Arizona whiteflies tested were highly susceptible to pyriproxyfen in 1996. The LC50 estimates were in the range of 0.002 to 0.007 g pyriproxyfen/ml. Two diagnostic pyriproxyfen concentrations, 0.01 and 0.1 g /ml, were established for efficient identification of resistant whiteflies. No resistance to pyriproxyfen was detected in whiteflies in statewide surveys conducted in 1997 and 1998. Mean mortality at 0.01 g/ml dropped significantly and survivors were detected for the first time at 0.1 g/ml in 1999, the fourth year of use of pyriproxyfen in Arizona cotton. Among the five cotton locations monitored each year since 1996, four of them had whiteflies with significantly reduced susceptibility to pyriproxyfen in 1999. Similarly, reduced susceptibility to pyriproxyfen was detected in whiteflies collected from fall melons, and greenhouses in 1999. Though there have been no reports of field failures of pyriproxyfen in Arizona cotton, the reduced susceptibility of whiteflies from statewide survey in 1999 was significant. The results may indicate the development of an early stage of resistance to pyriproxyfen, and the findings should serve as early warning and substantiation of the high resistance risk of pyriproxyfen.