Diamondback moth (Lepidoptera: Plutellidae) resistance to insecticides in Hawaii: intra-island variation and cross-resistance

Diamondback moth, Plutella xylostella (L.). larvae from 10 field populations in Hawaii were tested for susceptibility to DDT, diazinon, permethrin, and fenvalerate. Data were analyzed by probit methods and by ANOVA (analysis of variance), which has some advantages compared with probit and diagnostic dose tests for resistance. Relative to a laboratory strain, maximum resistance ratios at LC50 were 130 for DDT, 15 for diazinon, 5 for permethrin, and 3 for fenvalerate. Significant intra-island variation in susceptibility among populations occurred. Some populations separated by less than 10 km differed in susceptibility, but variation among islands was not significant. Results suggest that past selection by insecticides othen than pyrethroids (e.g., DDT and diazinon) caused some cross-resistance to permethrin. Sequences, rotations, and combinations of conventional insecticides are unlikely to retard resistance development in the diamondback moth due to cross-resistance. Management of the diamondback moth with pathogens, natural enemies, cultural controls, and limited insecticide use may slow evolution of resistance