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 thewestern 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 ofmagnitude
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 (34matches) than with that of A. bipunctata (six matches).