Stability and persistence of aldrin and methyl-parathion resistance in western corn rootworm populations (Coleoptera: Chrysomelidae)

The susceptibilities of laboratory and field-collected western corn rootworm populations (Diabrotica virgifera virgifera LeConte) to methyl-parathion and aldrin were estimated by topical application of insecticide during 2002 to determine the stability of resistance in the absence of selective pressures. Most of the laboratory-reared and field-collected populations were significantly resistant to both insecticides. Average LD50 values of laboratory and field-collected populations were 19- and 13-fold greater than the susceptible population in methyl-parathion bioassays, respectively, and 204- and 125-fold greater in the aldrin bioassays, respectively. The presence of aldrin and methyl-parathion resistance in field-collected populations strongly suggests that both resistance traits are stable in the absence of selection pressure and that neither mechanism is associated with a strong fitness disadvantage.