Malathion resistance in larvae of some southern Minnesota populations of the indianmeal moth, Plodia interpunctella (Lepidoptera: Pyralidae), infesting bulk-stored shelled corn

Larvae of 21 field collected populations of the Indianmeal moth, Plodia interpunctella , infesting stored shelled corn in southern Minnesota were tested for their susceptibility to malathion in the laboratory. A population that was a composite of the 21 populations and a malathion susceptible population were also tested for their susceptibility to malathion, pirimiphos-methyl and chlorpyrifos-methyl. Comparison of the LD sub(50) values of the field populations with the malathion susceptible population indicated that the field populations were ca. 33- to 625-fold resistant to malathion.