Oral RNAi reduces survival and grain loss in Rhyzopertha dominica, including phosphine-resistant populations.

BACKGROUND: Phosphine fumigation remains a cornerstone of stored-grain protection, yet widespread resistance in Rhyzopertha dominica threatens its long-term effectiveness. RNA interference (RNAi) through ingestion of double-stranded RNA (dsRNA) offers a sequence-specific mode-of-action (MoA) distinct from conventional insecticides. However, practical development requires identification of orally effective target genes, demonstration of grain-protection benefits, and validation of efficacy in phosphine-resistant populations. RESULTS: Oral delivery of dsRNA produced dose-dependent reductions in adult survival, with survival ranging from 3% to 12% among the five target-gene treatments at 300 ng μL-1 after 10 days of continuous exposure, compared with >90% in the controls. Target transcript levels were reduced to 15-48% of control levels following dsRNA exposure, confirming RNAi activity. dsRNA treatment also substantially reduced grain damage, with relative grain weight loss reduced to as low as 8% of the water-treated control at 300 ng μL-1. Oral RNAi remained effective across populations with different levels of phosphine resistance, with corrected mortality reaching ≈82% by Day 10 in the highly resistant population (RR = 1173.63). CONCLUSION: Oral RNAi can suppress R. dominica populations and reduce grain damage while maintaining efficacy in phosphine-resistant populations under the conditions tested. These findings support RNAi as a complementary MoA that may help diversify management options for stored-grain protection and resistance management. © 2026 The Author(s). Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.