Field resistance of Brazilian Plutella xylostella to diamides is not metabolism-mediated

Abstract

The indiscriminate use of chlorantraniliprole has led Plutella xylostella (L.) (Lepidoptera: Plutellidae) populations from northeast of Brazil to resistance. There is no information in Brazil about the current status of P. xylostella resistance to other diamides and the mechanisms underlying it. The study aimed to assess the susceptibility of P. xylostella from brassica producing areas in the northeast of Brazil to three diamides: chlorantraniliprole, cyantraniliprole and flubendiamide by estimating concentration-response curves. In addition, the activity of detoxification enzymes and their inhibition were examined to exclude their association with the resistance. Activity of three detoxification enzyme complexes was assessed: esterase, glutathione S-transferase and mixed function oxidase. Low mortality (0–10%) was observed among all assessed field populations at label doses, suggesting control failure in the field. Resistance ratios (RR50) for the populations varied from 7500- to 28 000-fold (chlorantraniliprole), from 12- to 2000-fold (cyantraniliprole), and from 2900- to 519 000-fold (flubendiamide). Cross-resistance among diamides was observed as expected. Significant synergism ratio [SR50 = 2.22 (1.57–3.14)] for chlorantraniliprole was observed only by diethylmaleate, though not enough to explain diamide resistance. Although enzymatic activities varied significantly among populations, no correlation with levels of susceptibility was observed and metabolic detoxification is not a major factor associated with diamide resistance in these populations, which may be explained by target site alteration. These results show that very high resistance to diamides quickly developed in these populations of P. xylostella. The findings of this study suggest that novel insecticides must be wisely used to avoid quick selection of resistance and loss of the efficacy in the field.