Bioinsecticides Induce Developmental Defects in Non-Target Larvae.

Bioinsecticides made from the bacterium () are the bestselling bioinsecticide worldwide. Among bioinsecticides, those based on the strain subsp. () are widely used in farming to specifically control pest lepidopteran larvae. Although there is much evidence of the lack of acute lethality of products for non-target animals, only scarce data are available on their potential non-lethal developmental adverse effects. Using a concentration that could be reached in the field upon sprayings, we show that products impair growth and developmental time of the non-target dipteran . We demonstrate that these effects are mediated by the synergy between bacteria and insecticidal toxins. We further show that bioinsecticides trigger intestinal cell death and alter protein digestion without modifying the food intake and feeding behavior of the larvae. Interestingly, these harmful effects can be mitigated by a protein-rich diet or by adding the probiotic bacterium into the food. Finally, we unravel two new cellular mechanisms allowing the larval midgut to maintain its integrity upon aggression: First the flattening of surviving enterocytes and second, the generation of new immature cells arising from the adult midgut precursor cells. Together, these mechanisms participate to quickly fill in the holes left by the dying enterocytes.