Susceptibility of the pine processionary caterpillar Thaumetopoea pityocampa (Lepidoptera : Thaumetopoeidae) toward delta-endotoxins of Bacillus thuringiensis under laboratory conditions

A series of natural crystal proteins from B. thuringiensis subsp. alesti 12 -25, caucasicus, galleriae 11-67, galleriae 6-96, kenyae, and shondungensis and spore-crystal preparations from finitimus 11-66 and from a recombinant strain of B. thuringiensis subsp. kurstaki expressing Cry1Ga1 only, were a ssessed as a toxic agent for the pine processionary caterpillar, Thaumetopo ea pityocampa. Some preparations had a thoroughly investigated composition and contained Cry1Aa, Cry1Ab2, Cry1Ab7, Cry1D, Cry1F, Cry1Ga1, Cry9Aa, Cry2 6 crystal proteins, whereas crystals of B. thuringiensis subsp. caucasicus, kenyae, and shondungensis harboured predominantly unidentified toxins dist ant from commonly used prototypes. Bioassays were based on the simultaneous assignment of each treatment to gr oups of 20 full sibling first-instar larvae, obtained from broods of a popu lation from North-western Italy. The toxin was applied to pine needles by t he leaf dipping method and the effect was registered in both feeding inhibi tion and mortality. B. thuringiensis subsp. caucasicus, kenyae, galleriae 6 -96, alesti, and galleriae 11-67 gave the best results in terms of both fee ding inhibition and larval mortality. Broods tested in B. thuringiensis bio assays showed a substantial variation in susceptibility to the toxins, sugg esting the potential development of resistance in the population.