Toxicity of Different Serotypes and Toxins of Bacillus thuringiensis to Resistant and Susceptible Indianmeal Moths (Lepidoptera: Pyralidae)1

Abstract

Fifty-seven isolates of Bacillus thuringiensis (BT) known to be toxic to larvae of Indianmeal moths, Plodia interpunctella (Hübner), were tested for activity against an Indianmeal moth colony resistant to the HD-l strain of BT. Twenty-one of the isolates, representing five of the eight serotypes tested, were active against the BT-resistant moths. Fifteen of the isolates, representing serotypes 4a,4c (kenyae), 6 (entomocidus), 7 (aizawai), 9 (tolworthi), and 10 (darmstadiensis), had no significant toxicity toward house flies, Musca domestica L., indicating that their toxicity toward the BT-resistant Indianmeal moths resulted from differences in the structure, composition, or function of the spore-crystal complex and not from exotoxin contamination. Bioassays confirmed that the Indianmeal moths were resistant to spores and crystals but susceptible to β-exotoxin.