The diamondback moth, Plutella xylostella (L.) (Lepidoptera: Plutellidae), is the main destructive insect pest of brassicaceous vegetables around the world. It has developed resistance to various classes of insecticides. However, the current status of insecticide resistance in P. xylostella has not been examined in China. In this study, concentration-mortality responses of P. xylostella to 8 insecticides, including abamectin, chlorantraniliprole, spinosad, beta-cypermethrin, chlorfenapyr, diafenthiuron, chlorfluazuron and the bio-pesticide Bacillus thuringiensis kurstaki (Btk) were evaluated. The results showed that almost all of the tested populations had developed high to very high resistance to abamectin and beta-cypermethrin, with resistance ratios ranging from 62.9 to 1494.7-fold. Chlorantraniliprole was very effective against P. xylostella in most tested populations except those from Taihe and Wuxi. Approximately 61% of tested populations displayed moderate resistance to spinosad, while other field populations showed minor changes (3-fold) in their susceptibility to this insecticide. Obvious variation (93-fold) of susceptibility to chlorfenapyr existed in field populations of which 32% displayed low level resistance, and 36% exhibited moderate resistance. Only one field population (Wuxi) showed very high resistance to chlorfenapyr (RR = 260.1). Diafenthiuron and chlorfluazuron were highly effective against all of the tested populations with resistance ratios (RR) ranging from 0.4 to 8.7 — fold. Decreased susceptibility ranging to moderate resistance to Btk was observed (RR = 3.8 – 35.3). Significant correlations were detected between the values of logLC50 of chlorantraniliprole and 4 insecticides (abamectin, spinosad, beta-cypermethrin and chlorfenapyr). The results of this study provided valuable information for choosing alternative insecticides and for integrated resistance management of P. xylostella.
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Vol. 98 • No. 1