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 single controlled acute exposures to a biopesticide containing Bacillus thuringiensis (Bt), to detect midgut changes until 96 h. Our findings show concentration-dependence of these changes, reflecting in different degrees on both mortality and behaviour. In particular, some midgut changes are also found 96 h after treatment. Our results show that the tested product does not affect survival at presumable environmental concentrations, so confirming the lesser toxicity of 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.