A laboratory bioassay was developed for determining the toxicity of spinosad, chlorfenapyr, and thiamethoxam against the eggplant flea beetle, Epitrix fuscula Crotch, on eggplant foliage. Four days after initial exposure, LC50 values were 1.99, 2.50, and 0.88 ppm for spinosad, chlorfenapyr, and thiamethoxam, respectively. By dividing the recommended field rate in ppm by the LC50 value, a field toxicity ratio was determined and ranged from 13.5 for spinosad to 73.9 for thiamethoxam. The high ratios suggest that field rates for all three insecticides could likely be reduced. This was supported by field studies in 2000 in which reduced rates of spinosad and thiamethoxam significantly reduced flea beetle numbers on eggplant. Mortality produced by thiamethoxam occurred more quickly than that for the other tested materials as shown with LT50 values of 1.8, 3.0, and 3.6 and days for thiamethoxam, chlorfenapyr, and spinosad, respectively. Persistence studies indicated that while all three of the tested compounds initially produced high levels of mortality, chlorfenapyr and thiamethoxam produced 50% or greater mortality after 6 d. Our data suggest that future management strategies for E. fuscula on eggplant can be successfully altered to meet the changing needs of the producer. Spinosad was recently registered, is effective against the E. fuscula, and offers a viable alternative to carbamate and pyrethroid insecticides. Thiamethoxam and chlorfenapyr offer high levels of toxicity to E. fuscula and upon registration will offer additional effective tools for management.
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Vol. 95 • No. 2