Baseline susceptibility to chlorantraniliprole of Brazilian populations of Plutella xylostella

Chlorantraniliprole, a new anthranilic diamide, is an insecticide that has recently been registered in Brazil to control several lepidopterans, including the diamondback moth, Plutella xylostella (L.). Chemical control of this pest has been particularly difficult because of its evolution of resistance to previous insecticide classes. To deploy a chlorantraniliprole resistance-monitoring program, the susceptibility of P. xylostella populations from different regions of Brazil was assessed using concentration-mortality bioassays before the commercial release of chlorantraniliprole. Mortality data were subjected to Probit analysis to estimate lethal parameters. Dosing by immersion or by spraying in a Potter tower were both suitable but topical application was not. All of the P. xylostella populations were highly susceptible to chlorantraniliprole (LC50 0.015–0.056 mg a.i./l of water) with those from the Northeast being the most tolerant. LC99 values were also low (0.065–0.281 mg a.i./l). The susceptibility variation among the populations was notably low, with the highest tolerance ratio being 3.8 fold, indicating a low variability of response among the Brazilian populations to this insecticide. A discriminating concentration of 0.3 mg a.i./l was obtained from the baseline data and proved to be effective for evaluating other populations, causing 100% mortality. The baseline data reflect the natural variation of these P. xylostella populations to chlorantraniliprole, rather than variations caused by previous exposure.

► Leaf dip is suitable to assess chlorantraniliprole toxicity to Plutella xylostella.
► Populations of Plutella xylostella were very susceptible to chlorantraniliprole.
► A diagnostic concentration of 0.3 mg a.i./l is recommended for monitoring resistance.