Bacillus thuringiensis bioinsecticides induce developmental defects in non-target Drosophila melanogaster larvae

Bioinsecticides made from the bacterium Bacillus thuringiensis (Bt) are the best-selling bioinsecticide worldwide. Among Bt bioinsecticides, those based on the strain Bt var. kurstaki (Btk) are widely used in farming to specifically control pest lepidopteran larvae. Although there is much evidence of the lack of acute lethality of Btk products for non-target animals, only scarce data are available on their potential non-lethal developmental adverse effects. Using doses that could be reached in the field upon sprayings, we have shown that Btk products impair growth and developmental time of the non-target dipteran Drosophila melanogaster. These effects are mediated by the synergy between Btk bacteria and Btk insecticidal toxins, which induces a significant apoptosis of larval enterocytes, resulting in a decreased intestinal capacity to digest proteins. The harmful effects can be mitigated by a protein-rich diet or by adding the probiotic bacterium Lactobacillus plantarum into the food. Finally, we showed that the larval midgut maintain its integrity upon Btk aggression thanks to both the flattening of surviving enterocytes and the generation of new immature cells arising from the adult midgut precursor cells.