Bacillus secretes nucleases to degrade dsRNA, thereby reducing host's susceptibility to RNAi.

RNAi technology, which can induce mortality by disrupting the transcription of essential growth and development-related genes in insects, has emerged as a groundbreaking pest control method. However, insects have developed defense mechanisms to counteract the efficiency of RNAi. The specific role of symbiotic microorganisms in this process remains poorly understood and requires further exploration. This study examines the reduced RNAi efficiency in Lepidopteran pest Helicoverpa armigera. Through screening, six Bacillus strains exhibiting dsRNA-degrading activity were identified through in vitro assays. Further investigation into one representative strain Ba 6 revealed that it significantly decreased RNAi efficiency by secreting ribonuclease into the insect gut fluid, directly degrading dsRNA, thus reducing its accumulation and blocking RNAi effects. These findings clarify the mechanism by which symbiotic bacteria influence the host's RNAi efficiency and provides a valuable reference for the development and large-scale implementation of RNA biopesticides targeting H. armigera and other lepidopteran pests.