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Relative susceptibility of Frankliniella occidentalis and Frankliniella intonsa to pesticides
The western flower thrips, Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae), has been considered as a major thrips species after its invasion in 1993 in Korea although recently F. intonsa (Trybom) was found as a dominant species locally. To explain their asymmetrical abundance in the field, we hypothesized differential insecticide susceptibility of both thrips species as an underlying mechanism. Laboratory assays were conducted to know their susceptibility to different pesticides including chlorfenapyr, chlorpyrifos, thiamethoxam, spinosad, s-metolachlor, and metalaxyl by direct spray, residue, and oral ingestion. Results showed that both thrips species were highly susceptible to chlorfenapyr and mortality reached 100% within 12 hours in F. occidentalis in all the assays while 9 hours in F. intonsa in direct spray and residual assays. The LT50[h] values of tested insecticides were significantly lower than that of herbicide or fungicide regardless of exposure methods except metalaxyl from direct spray. The insecticides tested here differed considerably in species specific toxicity, and F. intonsa is generally more susceptible to the insecticides irrespective of exposure methods.
