Model for Managing Resistance to Fenvalerate in the Diamondback Moth (Lepidoptera: Plutellidae)

ABSTRACf Evolution of resistance to the pyrethroid insecticide fenvalerate in the dia-mondback moth, Plutella xylostella (L.), was simulated by a computer model. Predictions from the model agree with data documenting development of diamondback moth resistance to fenvalerate in Ban-chau, Taiwan, in <4 years. Sensitivity analyses varying fecundity (4-fold), initial R gene frequency (10,OOO-fold),initial population density (lOO-fold),and per-centage of larvae escaping insecticide exposure (0-20%) resulted in predicted times for resistance development under Ban-chau conditions ranging from <1-4 years. Simulations of 15 management strategies suggest that under tropical conditions, spray frequency must be less than two per cabbage cycle or spray concentration less than the LC " of susceptible larvae to substantially delay resistance development. Adoption of alternative tactics for management of the diamondback moth is strongly urged. KEY WORDS insecticide resistance, pyrethroid, modeling, Plutella xylostella, cabbage pest management, fenvalerate, resistance management PESTRESISTANCEto insecticides threatens agricul-tural production and human health throughout th