BACKGROUND One concern with the adoption of RNAi‐based genetically engineered (GE) crops is the potential harm to valued non‐target organisms. Species of Coccinellidae (Coleoptera) are important natural enemies and might be exposed to the insecticidal dsRNA produced by the plant. To assess their susceptibility to dietary RNAi, we fed Adalia bipunctata and Coccinella septempunctata with a dsRNA designed to target the vATPase A of the western corn rootworm, Diabrotica virgifera virgifera (Dvv dsRNA). Specific dsRNAs designed to target the vATPase A of the two ladybird beetle species served as positive controls. RESULTS Our results revealed that both species were sensitive to dietary RNAi when ingesting their own dsRNAs, with C. septempunctata being more sensitive than A. bipunctata. Dvv dsRNA also adversely affected the two ladybird beetles as indicated by a significantly (but marginally) prolonged developmental time for A. bipunctata and a significantly reduced survival rate for C. septempunctata. These results, however, were obtained at Dvv dsRNA concentrations that were orders of magnitude higher than expected to occur in the field. Gene expression analyses confirmed the bioactivity of the dsRNA treatments and the results from the feeding bioassays. These results are consistent with the bioinformatics analyses, which revealed a higher number of 21‐nucleotide‐long matches, a requirement for effective RNAi, of the Dvv dsRNA with the vATPase A of C. septempunctata (34 matches) than with that of A. bipunctata (six matches). CONCLUSION Feeding bioassays revealed that two ladybird species are responsive to dietary RNAi. The two species, however, differed in their sensitivity. © 2019 Society of Chemical Industry

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.

Potentially adverse effects on ecosystem functioning by the planting of insect-resistant, genetically engineered plants or by the direct application of insecticidal compounds are carefully evaluated in pre-market risk assessments. To date, few studies have assessed the potential risks of genetically engineered crops or insecticidal compounds on the survival and fitness of dipteran species, despite their important contribution to ecosystem services such as decomposition in agricultural systems. Therefore, we propose that Drosophila melanogaster Meigen (Drosophilidae) be used as a surrogate species for the order Diptera and for the functional guild of soil arthropod decomposers in pre-market risk assessments. We developed two assays to assess the toxicity of gut-active insecticidal compounds to D. melanogaster. One assay uses groups of fly larvae, and the other uses individuals. Cryolite, a mineral pesticide, proved to be an adequate positive control. The effects of cryolite on D. melanogaster larvae were comparable between the two assays. Statistical power analyses were used to define the number of replications required to identify different effect sizes between control and treatment groups. Finally, avidin, E-64, GNA, and SBTI were used as test compounds to validate the individual-based assay; only avidin adversely affected D. melanogaster. These results indicate that both D. melanogaster assays will be useful for early tier risk assessment concerning the effects of orally active compounds on non-target dipterans.

No abstract

No abstract