No adverse effect of an insecticidal dsRNA on nymphal survival and development of insidiosus flower bugs, Orius insidiosus (Heteroptera: Anthocoridae)

The insidious flower bug, Orius insidiosus (Say) (Heteroptera: Anthocoridae), is an important biological control agent in many cropping systems and is considered to be an important surrogate predatory insect species in evaluating the impact of plant-incorporated protectants (PIPs) expressed in GM crops.  In this study, we assessed the potential effect of a dsRNA on O. insidious nymphs using a Tier-1 laboratory testing system we developed previously.  The dsRNA causes down-regulation of the targeted gene in western corn rootworm (WCRW), Diabrotica virgifera virgifera LeConte (Coleoptera: Chrysomelidae), and results in WCRW mortality.  No mortality was observed to Orius nymphs that consumed the treated diet containing the WCRW-targeted dsRNA at 5.0 mg/ml diet, a concentration level equivalent to approximately 1000 times the 12-Day LC₅₀ value for WCRW.  Additionally, the development time of test nymphs to adults showed no significant difference between the control diet and the dsRNA treated diet with mean development times to adult of 10.7 days.  However, high mortality was observed by Day 9 in the positive control (potassium arsenate, 50µg/ml diet), confirming the effectiveness of this dietary exposure system to detect the potential for toxicity through dietary exposure.  The results of this study indicate that continuous dietary feeding exposure to the dsRNA, at a concentration level that provides a large margin of safety, has no adverse effect on the survival and development of O. insidiosus nymphs.