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

Abstract

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. honeybees / Bacillus thuringiensis var. aizawai /kurstaki / bioassay / mortality / morphostructural changes Electronic supplementary material The online version of this article (

Possible interference of Bacillus thuringiensis in the survival and behavior of Africanized honey bees (Apis mellifera)

“…The survival of A. mellifera worker bees fed with a product based on B. thuringiensis var. aizawai and kurstaki at different concentrations (field dose 100.0 g/hL; low concentration, 40.00 g/hL; and very high concentration, 24,400.00 g/hL); selectivity was found at low concentration (40.00 g/hL) because it did not induce the death in Africanized honey bees at the end of 96 h 32 . The field dose (100.0 g/hL) caused resulted in a mortality rate of 5%, which was not significantly different from the control, whereas the high concentration (24,400.0 g/hL) resulted in a mortality rate of 15% at the end of the experimental period, which was significantly different from the control 32 .…”

“…aizawai and kurstaki at different concentrations (field dose 100.0 g/hL; low concentration, 40.00 g/hL; and very high concentration, 24,400.00 g/hL); selectivity was found at low concentration (40.00 g/hL) because it did not induce the death in Africanized honey bees at the end of 96 h 32 . The field dose (100.0 g/hL) caused resulted in a mortality rate of 5%, which was not significantly different from the control, whereas the high concentration (24,400.0 g/hL) resulted in a mortality rate of 15% at the end of the experimental period, which was significantly different from the control 32 . In other studies, the comparison of three strains of B. thuringiensis (IPS 82, BR 81, and BR 147), all reduced the survival of Africanized honey bees ( A. mellifera ) workers when incorporated into the diet 33 owing to the mode of action of bacteria in insects.…”

“…kurstaki HD-1 42 and in studies with larvae that were fed diets containing B. thuringiensis proteins (Cry1C or Cry2A) 43 . However, D’Urso et al 32 found that changes in the intestine had occurred at 96 h after treatment with B. thuringiensis . Some acute effects may occur in the long term in the intestinal epithelium of the bees that have ingested Bt, despite the apparent absence of toxicity (i.e., no alteration in survival of the bees).…”

“…Some acute effects may occur in the long term in the intestinal epithelium of the bees that have ingested Bt, despite the apparent absence of toxicity (i.e., no alteration in survival of the bees). This may mask other physiological disruptions that are harmful to bees, particularly in the case of exposure to biological products in combination with other environmental stressors 32 , 44 .…”

Sublethal effects of commercial plant protection product containing spores Bacillus amyloliquefaciens QST 713 (formerly subtilis) on winter adult honeybees

“…Also, the effect of different B. thuringiensis strains on the longevity of Africanized honeybee is reported (Libardoni et al 2018). Pathological observations on midgut (the irregular epithelium profile, numerous irregular cellular fragments of different sizes interspersed with the fibrils of the peritrophic membrane) of adult worker bees under controlled acute exposure to a Bacillus thuringiensis -based biopesticide were observed (D'Urso et al 2017). Except for the laboratory studies, also the field assessment on the colony performance after aerial application of Bacillus thuringiensis subsp.…”