NERVE INSENSITIVITY RESISTANCE TO PYRETHROIDS IN HELIOTHINE LEPIDOPTERA

A neurophysiological assay developed previously was used to assess the incidence of nerve insensitivity resistance to synthetic pyrethroids in field strains of Helicoverpa armigera. Almost 70% of individuals fr om a sample of a highly pyrethroid-resistant population from Jiangsu P rovince, China were nerve-insensitive. Subsequent selection resulted i n a strain homogeneous for expression of this mechanism. Likewise, ove r 95% of a sample from a strain of the insects from Andhra Pradesh, In dia were nerve-insensitive and a homogeneous strain was developed. Dev elopment of a nerve-insensitive laboratory strain of Heliothis viresce ns was undertaken but homozygosity could not be obtained. It is sugges ted that high fitness costs may be associated with this mechanism. The incidence of nerve insensitivity in Heliothine pests is reviewed and the role of phenotypic expression assays in molecular studies highligh ted.