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Title: INTER-REGIONAL DIFFERENCES IN BASELINE TOXICITY OF BEMISIA ARGENTIFOLII (HOMOPTERA: ALEYRODIDAE) TO THE TWO INSECT GROWTH REGULATORS BUPROFEZIN AND PYRIPROXYFEN

Author
item TOSCANO, NICK - UNIV CA, RIVERSIDE
item PRABHAKER, NILIMA - UNIV CA, RIVERSIDE
item Castle, Steven
item Henneberry, Thomas

Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/1/2001
Publication Date: 2/1/2002
Citation: Toscano, N.C., Prabhaker, N., Castle, S.J., Henneberry, T.J. 2002. Inter-regional differences in baseline toxicity of bemisia argentifolii (homoptera: aleyrodidae) to the two insect growth regulators buprofezin and pyriproxyfen. Journal of Economic Entomology 94:1538-1546.

Interpretive Summary: Silverleaf whitefly (SLWF) populations have devastated agricultural crops in California and Arizona causing damage of over $200 million annually. Resistance to every class insecticide chemistry is known. Baseline toxicity responses of 53 populations to buprofezin and pyriproxyfen showed temporal differences using a leaf spray bioassay technique. Six to seven populations had higher LC_50 values over time, but not greater survival when exposed to the two insecticides. A difference in relative susceptibility to buprofezin in 1997 in San Joaquin Valley showed LC_50S ranging from 16 to 22 mg (AI)/liter^-l compared with LC_50s of l to 3 mg (AI)/liter^-l in Imperial, Palo Verde and Yuma Valley. In subsequent years SLW from these and other locations showed an increase in buprofezin susceptibility. Regional differences in susceptibilities to pyriproxyfen at the same location were minimal. SLWF LC_50S to pyriproxyfen were higher from Palo Verde Valley, CA, compared with Imperial, San Joaquin Valley or Yuma. LC_50s declined at all locations in 1999. However, no correlation was observed between buprofezin and pyriproxyfen toxicity in any of the strains. Toxicity differences may be due to inherent geographical differences or past chemical use which may confer positive or negative cross-resistance.

Technical Abstract: A survey of 53 Bemisia argentifolii Bellows & Perring populations from different agricultural regions in California and Arizona was conducted from 1997 to 1999 to establish baseline toxicological responses to buprofezin and pyriproxyfen. Although both compounds proved to be highly toxic even in minute quantities to specific stages, geographical and temporal differences in responses were detected using a leaf spray bioassay technique. Monitoring for three years revealed that six to seven populations had higher LC50 values but not greater survival when exposed to these two insecticides. A significant difference in relative susceptibility to buprofezin was first observed in late season 1997 in San Joaquin Valley populations with LC_50S ranging from 16 to 22 mg (AI)/liter^-l compared with LC_50s of l to 3 mg (AI)/liter^-l in Imperial, Palo Verde Valley and Yuma populations. Whiteflies collected in subsequent years from these and other locations showed an increase in susceptibility to buprofezin. Regional differences in susceptibilities to pyriproxyfen were minimal within the same years. Three years of sampling revealed consistently higher LC_50S to pyriproxyfen in populations from Palo Verde Valley, CA, compared with whiteflies from Imperial, San Joaquin Valley or Yuma. As was the case with buprofezin, a decline in LC_50s to pyriproxyfen was observed in whiteflies from all locations sampled in 1999. However, no correlation was observed between buprofezin and pyriproxyfen toxicity in any of the strains. The variable toxicities observed to both compounds over a period of 3 yr may be due principally to inherent differences among geographical populations or due to past chemical use which may confer positive or negative cross-resistance to buprofezin or pyriproxyfen.