Bacillus thuringiensis Bioinsecticides Induce Developmental Defects in Non-Target Drosophila melanogaster Larvae

Abstract

Bioinsecticides made from the bacterium Bacillus thuringiensis (Bt) are the bestselling bioinsecticide worldwide. Among Bt bioinsecticides, those based on the strain Bt subsp. 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 a concentration that could be reached in the field upon sprayings, we show that Btk products impair growth and developmental time of the non-target dipteran Drosophila melanogaster. We demonstrate that these effects are mediated by the synergy between Btk bacteria and Btk insecticidal toxins. We further show that Btk 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 Lactobacillus plantarum into the food. Finally, we unravel two new cellular mechanisms allowing the larval midgut to maintain its integrity upon Btk 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.

Bacillus thuringiensis Cry1A toxins divert progenitor cells toward enteroendocrine fate by decreasing cell adhesion with intestinal stem cells

“…Drosophila were reared on standard medium (0.8% Agar, 2.5% sugar, 8% corn flour, 2% yeast) at 25 ° C with a 12h light/12h dark cycle. For oral infection, after 2 h of starvation to synchronize the food intake, ten 5 to 6 day-old non-virgin females were transferred onto a fly medium vial covered with a filter disk soaked with water (control) or a suspension of spores, (corresponding to 10 6 CFU of spores per 4 cm 2 and per individual female (Loudhaief et al, 2017; Nawrot-Esposito et al, 2020)), crystals, protoxin or activated toxins. The quantity of crystals, protoxin or activated toxins deposited on the filter disc corresponded to 30% of the spore weight, Btk crystals representing between 25% and 30% of the total weight of the 1:1 spore/crystal mix (Agaisse and Lereclus; 1995; Monroe, (1961); Murty et al, 1994).…”

“…Recent studies provide evidences that Btk also exhibits some adverse effects on non-susceptible organisms. First, we have shown that Btk spores and toxins at concentrations close to those recovered on vegetables after spraying induce growth defects and developmental delay in Drosophila larvae (Nawrot-Esposito et al, 2020). Increasing spore and toxin doses ultimately led to larval lethality (Babin et al, 2020).…”

“…Recently, Bt has also been implicated in foodborne outbreak events and the strains identified were indistinguishable from the commercial ones (Biggel et al, 2021; Bonis et al, 2021; Johler et al, 2018). Furthermore, we have shown that Btk spores and toxins at concentrations close to those recovered on vegetables after spraying induce growth defects and developmental delay in Drosophila larvae (Nawrot-Esposito et al, 2020). Increasing spore and toxin doses ultimately led to larval lethality (Babin et al, 2020).…”

Determination, distribution, and environmental fate of Bacillus thuringiensis spores in various honeybee matrices after field application as plant protection product

“…Although Bt strains are assumed to be selective on target pests, recent reports indicate cross-order effects (van Frankenhuyzen et al 2017). For example, the Coleopteran-targeted formulation can cause negative effects on Lepidopteran (Redmond et al 2020), the Lepidopteran-targeted formulation on Coleopteran and the Dipteran (Coyle et al 2000;Babin et al 2020;Nawrot-Esposito et al 2020), and Diptera-targeted formulation on Coleopteran (Tudoran et al 2020). Regarding the effects on bees, differences in the sensitivity of adult worker bees to different Bt products were reported (Brighenti et al 2007;Mommaerts et al 2010;D'urso V, Mazzeo G, Vaccalluzzo V, Sabella G, Bucchieri F, Viscuso R, Vitale DG, , 2017;Libardoni et al 2018;Potrich et al 2018;Steinigeweg et al 2021).…”

“…The most studied insecticidal toxins are Cry-toxins as δ-endotoxins affecting the susceptible insects after oral uptake (Bravo et al 2011 andBravo et al, 2017;Mendoza-Almanza et al 2020). Several reports regarding direct and indirect cross-effects of Bt formulations and their toxins across insect taxa and orders recently indicated the semi-specificity of Bt (van Frankenhuyzen 2017; Redmond et al 2020;Coyle et al 2000;Babin et al 2020;Nawrot-Esposito et al 2020;Tudoran et al 2020). Lepidopterantargeted formulation, containing Bta ABTS 1857, has demonstrated increasing mortality of adult and larvae of honeybees after chronic exposure under laboratory conditions (Steinigeweg et al 2021).…”