ESTIMATING RESISTANCE TO METHOMYL IN THE TOMATO PINWORM (LEPIDOPTERA,GELECHIIDAE) USING A PHEROMONE TRAP BIOASSAY

The tomato pinworm, Keiferia lycopersicella (Walsingham), is an import ant pest of tomatoes in the southern and southwestern United States an d Mexico. A field-based method for assessing resistance of adults to t he carbamate insecticide, methomyl, was developed by incorporating var ying doses of technical insecticide into the adhesive of pheromone tra ps. The mortalities of male and female adults were similar whether exp osed to methomyl, either by topical or pheromone trap bioassays. Larva e were less susceptible than adults to methomyl by topical application . Therefore, adult male susceptibility provides a good estimate of adu lt female susceptibility but may overestimate larval susceptibility. N evertheless, using the pheromone trap bioassay and making comparisons of field populations with a laboratory strain suggested that all field populations evaluated were less susceptible to methomyl than the labo ratory strain. Populations in Mexico were more susceptible than popula tions in California, where methomyl is used more often. Populations in Florida were either intermediate in susceptibility or were similar to those in California. Copyright (C) 1996 Elsevier Science Ltd.