Variation in susceptibility of Diadegma insulare (Hymenoptera : Ichneumonidae) to permethrin

Six field populations of the parasitoid Diadegma insulare (Cresson) were co llected from Mexico and the United States and tested for their susceptibili ty to permethrin by using a glass-vial residue bioassay. Significant differ ences existed in susceptibility. with one population significantly more sus ceptible than the other five. Susceptibility of D. insulare increased when they were reared for several generations in the greenhouse in the absence o f selection. D. insulare was less suceptible to permethrin than the adult s tage of its host, Plutella xylostella (L.), from a laboratory colony, but m ore susceptible than those hosts collected from a commercial field. Our dat a suggest that a field population of D. insulare appeared to increase its t olerance to permethrin much more slowly than P. xylostella.