Inheritance of resistance and cross-resistance to deltamethrin in Plutella xylostella (Lepidoptera: Plutellidae) from Pakistan

A field population of Plutella xylostella (L) from Pakistan was found to be highly resistant to deltamethrin (> 500-fold) but had little or no resistance to spinosad, fipronil, indoxacarb, abamectin, Bacillus thuringiensis (Bt) var kurstaki, Bt var aizawai or Cry1Ac when compared with a susceptible laboratory population, Lab-UK. A sub-population was selected for six generations (laboratory G(3)-G(8)) with deltamethrin (delta-SEL), while a second sub-population was left unselected (UNSEL). Bioassays at G(9) found that selection with deltamethrin gave resistance ratios of > 230 compared with UNSEL (> 6730 compared with Lab-UK). The delta-selected population showed no apparent cross-resistance to spinosad, fipronil or indoxacarb. Logit regression analysis of F, reciprocal crosses between delta-SEL and Lab-UK indicated that resistance to deltamethrin in the delta-SEL population was inherited as an autosomal, incompletely dominant (D-LC = 0.67) trait. A direct test of monogenic inheritance based on a back-cross of F-1 progeny with delta-SEL suggested that resistance to deltamethrin was controlled by more than one factor. (c) 2005 Society of Chemical Industry