Abstract
We investigated susceptibility to two diamide and ten other insecticides in four local populations of the diamondback moth, Plutella xylostella collected from cabbage (Brassica oleracea var. capitata) fields in Asahi City, a rape flower (Brassica rapa var. nippo-oleifera) field and a daikon (Raphanus sativus var. longipinnatus) field in Minamibousou City from October to December 2013 in Chiba Prefecture. For the larvae of two Asahi populations, fed with cabbage leaf disks treated with flubendiamide or chlorantraniliprole, the corrected mortalities at 72 hours after treatment were zero and the leaf areas damaged by the larvae were not significantly different from that of the control, showing a reduced susceptibility to these diamide insecticides. On the other hand, these diamide insecticides were highly effective against two Minamibousou populations. Spinetoram, emamectin benzoate, indoxacarb, tolfenpyrad, Bt and cartap hydrochloride were highly effective against all four populations.
