Differential side-effects of Bacillus thuringiensis bioinsecticide on non-target Drosophila flies

Abstract

Biopesticides based on Bacillus thuringiensis (Bt) spores and toxins are alternate pest management solutions widely used to control insect pests. Their increasing use could lead to accumulation in the environment, hence leading to chronic exposure of non-target organisms. Here, we tested for potential non-intentional side-effects of chronic exposure to Bt biopesticide on larvae of non-target Drosophila species present in Bt-treated areas. Doses up to those recommended for field application (106 CFU/g of fly medium) had no effect on the fly development, whereas doses 10 to 100-fold higher (107-108 CFU/g) increased developmental time and decreased adult emergence rates in a dose-dependent manner and with varying effect amplitudes for all the species and strains tested. For all them, all larvae died before pupation at the highest dose tested (109 CFU/g). Focusing on D. melanogaster, delayed development and reduced emergence resulted from stage-dependent larval mortality, and fitness-related traits of adult flies emerging from surviving Bt biopesticide exposure were moderately increased. The effects of Bt biopesticide seemed to result from the spores/cleaved toxins synergy, and possibly additives. While recommended doses had no effect on non-target Drosophila species, misuse or local accumulation of Bt bioinsecticides in the environment could have non-intentional side-effects on fly populations with potential implications for their associated communities.