BIOASSAY FOR DETECTING PYRETHROID NERVE INSENSITIVITY IN AUSTRALIAN HELICOVERPA-ARMIGERA (LEPIDOPTERA, NOCTUIDAE)

A simple locomotory knockdown bioassay was used to detect Kdr-like ner ve insensitivity to pyrethroids in pyrethroid resistant Australian cot ton bollworms, Helicoverpa armigera (Hubner), larvae. Resistant popula tions with high-level nerve insensitivity had >250-fold resistance to knockdown compared with susceptible populations. Pyrethroid resistant populations without nerve insensitivity were only 2.5 times more resis tant to knockdown than susceptible individuals. Use of a discriminatin g dose, slightly in excess of the KD100 of the resistant strains lacki ng nerve insensitivity, is suggested as an easy, rapid method to monit or for nerve insensitivity to pyrethroids in H. armigera larvae.