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1 June 2013 Monitoring Changes in Bemisia tabaci (Hemiptera: Aleyrodidae) Susceptibility to Neonicotinoid Insecticides in Arizona and California
S. J. Castle, N. Prabhaker
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Bemisia tabaci (Gennadius) biotype B is a highly prolific and polyphagous whitefly that established in much of North America during the 1980s. Neonicotinoid insecticides have been fundamental in regaining control over outbreak populations of B. tabaci, but resistance threatens their sustainability. Susceptibility of B. tabaci in the southwestern United States to four neonicotinoid insecticides varied considerably across populations within each year over a 3 yr period. Using a variability ratio of highest LC50 to lowest LC50 in field-collected whitefly adults from Arizona and California, the ranges of LC50s across all tests within compounds were highest to imidacloprid and lowest to thiamethoxam. Patterns of susceptibility were similar among all four neonicotinoid insecticides, but the greater variability in responses to imidacloprid and significantly higher LC50s attained indicated higher resistance levels to imidacloprid in all field populations. Further evidence of differential toxicities of neonicotinoids was observed in multiple tests of dinotefuran against imidacloprid-resistant lab strains that yielded significant differences in the LC50s of dinotefuran and imidacloprid in simultaneous bioassays. To test the possibility that resistance expression in field-collected insects was sometimes masked by stressful conditions, field strains cultured in a greenhouse without insecticide exposure produced significantly higher LC50s to all neonicotinoids compared with LC50s attained directly from the field. In harsh climates such as the American southwest, resistance expression in field-collected test insects may be strongly influenced by environmental stresses such as high temperatures, overcrowding, and declining host plant quality.

© 2013 Entomological Society of America
S. J. Castle and N. Prabhaker "Monitoring Changes in Bemisia tabaci (Hemiptera: Aleyrodidae) Susceptibility to Neonicotinoid Insecticides in Arizona and California," Journal of Economic Entomology 106(3), 1404-1413, (1 June 2013).
Received: 9 August 2012; Accepted: 15 February 2013; Published: 1 June 2013

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desert environment
host plant
insecticide resistance
systemic uptake bioassay
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