Development of a chitin synthesis inhibitor resistance in the diamondback moth, Plutella xylostella (L.) (Lepidoptera: Yponomeutidae). 2. The result of susceptibility tests

Abstract

The susceptibility of diamondback moth (DBM) collected from Mizobe, Kagoshima Prefecture to two chitin synthesis inhibitors was determined by the leaf-dipping method using 3rd instar larvae. Larvae were collected twice a year (Apr. and Nov.) during the period from 1989 to 1991. The DBM showed a high level of resistance against chlorfluazuron and teflubenzuron. The LCso values to chlorfluazuron increased from 11. 8 ppm in Nov. 1989 to 329 ppm in Nov. 1991. Teflubenzuron resistance first appeared in Apr. 1990 (LCso=23.9 ppm) ; the LCso value increased to 69. 4 ppm in Nov. 1991 despite the absence of spraying in the field, suggesting cross resistance between chlorfluazuron and teflubenzuron. The resistance level of both insecticides fluctuated seasonally: the resistance level was low in spring and high in autumn.