Effects of purified or plant-produced Cry proteins on Drosophila melanogaster (Diptera: Drosophilidae) larvae

Abstract

Although genetically engineered crops producing insecticidal Cry proteins from Bacillus thuringiensis (Bt) are grown worldwide, few studies cover effects of Bt crops or Cry proteins on dipteran species in an agricultural context. We tested the toxicity of six purified Cry proteins and of Bt cotton and Bt maize tissue on Drosophila melanogaster (Diptera: Drosophilidae) as a surrogate for decomposing Diptera. ELISA confirmed the presence of Cry proteins in plant material, artificial diet, and fly larvae, and concentrations were estimated. Median concentrations in emerging adult flies were below the limit of detection. Bioactivity of purified Cry proteins in the diet was confirmed by sensitive species assays using Heliothis virescens (Lepidoptera: Noctuidae). Purified Cry1Ab, Cry1Ac, Cry1B, Cry1C, Cry1F, or Cry2Aa, or leaf material from stacked Bt cotton (Bollgard II producing Cry1Ac and Cry2Ab) or Bt maize (SmartStax producing Cry1A.105, Cry1Fa2, Cry2Ab2, Cry3Bb1, Cry34Ab1 and Cry35Ab1) had no consistent effects on D. melanogaster survival, developmental time, adult body mass or morphometrics. However, D. melanogaster showed longer developmental time and smaller wing size when fed with cotton leaves from plants infested with H. virescens caterpillars compared to flies fed with leaves from uninfested plants, while no such effects were obvious for maize.

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

“…Our data show that the impacts are mainly due to the synergy between Btk spores and crystals since either the spores ( Btk ΔCry ) or the purified crystals alone do not promote detectable developmental delay or growth defects in Drosophila larvae. This is in agreement with the study analyzing the safety of Btk purified Cry toxins on Drosophila larval development [ 18 ].…”

“…The increasing environmental dispersion of Btk bioinsecticides and the persistence of the spores in the environment [ 13 , 14 , 15 , 16 ] raise the question of their long-term putative effects on both health and environment. There are many data sets showing that Btk spores and Cry toxins do not display harmful effects against non-target organisms [ 17 , 18 ]. Nevertheless, there are also studies suggesting that Btk spores and crystals may have unintended impacts on non-target animals.…”

Bacillus thuringiensisbioinsecticides induce developmental defects in non-targetDrosophila melanogasterlarvae

“…Nonetheless, the impacts are mainly due to the synergy between Btk spores and crystals since either the spores (Btk ΔCry ) or the purified crystals alone do not promote detectable developmental delay or growth defects in Drosophila larvae. These data are in agreement with the study analyzing the safety of Btk purified Cry toxins on Drosophila larval development (Haller et al, 2017).…”

“…The increasing environmental dispersion of Btk bioinsecticides raises the question of their long-term putative effects on both health and environment. Although there are many data showing that the Cry toxins produced by Btk do not display harmful effects against non-target organisms (Haller et al, 2017;Rubio-Infante and Moreno-Fierros, 2016), there are also studies suggesting that Cry toxins and/or Bt products may have unintended impacts on nontarget animals. For example, the presence of Cry1Ab toxins produced by GM maize in water streams surrounding maize fields delays the growth and increases the mortality of trichopteran species whose larvae have an aquatic lifestyle (Rosi-Marshall et al, 2007;Tank et al, 2010).…”

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

“…However, most of them suggested susceptibility to Btk, but they used mainly late 3rd instar larvae preparing for pupation, which do not feed much. In addition, these studies used Bt preparations, especially field isolates, that possibly contained highly toxic β-exotoxins, which are not authorized in commercial Bt formulations [40][41][42][43][44][45][46][47] . So far, no study addressed the effects of chronic exposure to commercial Bt formulations on developing stages of these Dipterans that are present in Bt-treated areas.…”