Citrus Thrips (Thysanoptera: Thripidae) Resistance Monitoring in California

Abstract

Tolerance of adult female citrus thrips, Scirtothrips citri (Moulton), to chlorfenapyr, cyfluthrin, and spinosad was monitored at 10 sites in California in 1996. Chlorfenapyr and spinosad have yet to be used commercially in California and baseline LC90s were estimated to assist in future resistance monitoring efforts. The LC90s for chlorfenapyr ranged from 0.505 to 4.13 mg (AI)/liter and for spinosad from 2.09 to 5.37 mg (AI)/liter. On California citrus, cyfluthrin use, 1991-1996, has been restricted to the San Joaquin Valley and to a single application per year on navel oranges. Compared with the LC90 from the most susceptible site outside the San Joaquin Valley, resistance ratios ranged from 6.2 to 56.6 at 4 sites within the valley. The 56.6-fold resistance observed at the site in Kern County is a cause for concern and may be the result of citrus thrips exposure to pyrethroids applied to nearby cotton and vegetables. Strategies for slowing further escalation of pyrethroid resistance are discussed.