Stability of fenvalerate resistance in the leafminer parasitoid Diglyphus begini (Hymenoptera: Eulophidae)

We studied the stability of field-selected resistance to fenvalerate in Diglyphus begini (Ashmead), a major parasitoid of Liriomyza spp. leafminers. After up to 10 mo of laboratory rearing without exposure to insecticide, the LC50 to fenvalerate declined significantly in females, but not in males. Adults of both sexes from resistant colonies remained significantly less susceptible than adults from susceptible colonies and showed low mortality at concentrations equivalent to field-recommended application rates of fenvalerate. Comparison with previously reported data suggests that resistance in D. begini is not less stable than resistance in the leafminer Liriomyza trifolii (Burgess). The persistence of resistance in D. begini may be especially valuable in integrated pest management programs that use pyrethroids intermittently