Susceptibility of a malathion-resistant strain of Indianmeal moths (Lepidoptera:Pyralidae) to Bacillus thuringiensis berliner [Plodia interpunctella, biological control]

A malathion-resistant strain of Plodia interpunctella (Huebner) (IMM), was tested for susceptibility to B. thuringiensis Berliner (Bt). Five different instars were exposed to six concentrations of Dipel and Thuricide by mixing each formulation in a turkey-mash-based culture medium which served as the food. Early instars were more susceptible than the later instars to Bt (P < 0.01) while all were more susceptible to Dipel than to Thuricide (P < 0.001). The period of growth and development of the larvae was extended by exposure to the Bt from each formulation. Differences in larval susceptibility to Bt may result from the immunity and behavior of the larvae or the relative potency and repellency of Dipel versus Thuricide.