Diamondback Moth (Lepidoptera: Plutellidae) in South Texas: A Technique for Resistance Monitoring in the Field

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Abstract
In laboratory bioassays with selected insecticides labeled for application to cabbage, responses of field populations of diamondback moth larvae (Plutella xylostella (L.)), were compared with the response of a population in culture at the Texas A&M University Experiment Station, Weslaco. Insecticides tested were permethrin (pyrethroid), endosulfan (cyclodiene), methomyl (carbamate), methamidophos (organophosphate), and Bacillus thuringiensis Berliner (biological). At the LC90, resistance ratios were 13 for permethrin and 145 for methamidophos. This is the first documented occurrence of resistance to synthetic insecticides in North American diamondback moth larval populations. Results from bioassays with the susceptible colony were used to develop a field technique for monitoring diamondback moth larvae insecticide resistance in the field. The technique appears to be useful in making decisions about insecticide application in production fields in south Texas.