Observations on midgut of Apis mellifera workers (Hymenoptera: Apoidea) under controlled acute exposures to a Bacillus thuringiensis-based biopesticide.

Morphostructural investigations have been carried out on Apis mellifera workers treated with singlecontrolled acute exposures to a biopesticide containing Bacillus thuringiensis (Bt ), to detect midgut changes until96 h. Our findings show concentration-dependence of these changes, reflecting in different degrees on bothmortalityand behaviour. In particular, some midgut changes are also found 96 h after treatment. Our results show that thetested product does not affect survival at presumable environmental concentrations, so confirming the lesser toxicityof Bt -based biopesticides compared to other pesticides. However, in the light of the discovered long-term changes,we discuss the opportunity of taking into account possible chronic exposures to Bt -based products on A. mellifera .