The toxicity and physiological effects of Bacillus thuringiensis toxins and formulations on Thaumetopoea pityocampa, the pine processionary caterpillar

Toxicity of Bacillus thuringiensis Cry1B, Cry1C, and Cry1E toxins and B. th uringiensis-based bioinsecticides (Cordalene, Dipel, Foray 48B, and Foray 7 6B) was investigated in Thaumetapoea pityocampa (precessionary moth) larvae . Cry1B was toxic, while Cry1C and Cry1E were nontoxic. The toxicity of: th e bioinsecticides analyzed was of the same magnitude as that of the active purified toxins and determined mainly by one of the toxins present in the b ioformulate. We also demonstrated that only the active toxins were able to produce cytotoxic effects on the midgut epithelial cells and specifically b ound to T. pityocampa brush border membrane. Analysis of the receptor model of the active toxins showed that Cry1B did not compete for the Cry1A bindi ng site. This finding provides useful information for optimizing the use of B. thuringiensis toxins against Cry1C pityocampa. (C) 1999 Academic Press.