Injection, soaking, and oral delivery systems induce RNA interference-mediated silencing in the mealybug, Ferrisia gilli Gullan (Hemiptera: Pseudococcidae)

Authors: Bansal, Raman; Fernandez, Esther

Submitted to: Pest Management Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/28/2025
Publication Date: 4/17/2025
Citation: Bansal, R., Fernandez, E.M. 2025. Injection, soaking, and oral delivery systems induce RNA interference-mediated silencing in the mealybug, Ferrisia gilli Gullan (Hemiptera: Pseudococcidae). Pest Management Science. Available: https://doi.org/10.1002/ps.8826.
DOI: https://doi.org/10.1002/ps.8826

Interpretive Summary: Pistachio growers in California are facing a growing problem with Gill’s mealybug (GMB) as traditional pesticides are becoming less and less effective. Here, a new approach called RNA interference (RNAi) was investigated for its functionality in GMB. RNAi for pest management works by targeting specific genes crucial for insect survival. To deliver RNAi-inducing molecules to GMB, three methods injection, soaking, and oral delivery were tested in the laboratory. All delivery methods induced RNAi response with a varying degree and injection was most effective in reducing the target gene expression. The oral delivery via topical-feeding method, which involved applying the RNAi molecules directly on GMB's mouth, showed promising results. Overall, this study demonstrated that the RNAi is functional in GMB. The topical-feeding delivery method optimized here can be adopted and scaled for laboratory testing of RNAi gene targets for eventual field application.

Technical Abstract: BACKGROUND The mealybug Ferrisia gilli Gullan (Hemiptera: Pseudococcidae) has emerged as a major pest on pistachio in California. The indiscriminate use of a select group of chemicals has limited the effectiveness of available options to control F.'gilli. RNA interference (RNAi) represents a novel mode-of-action to provide an alternative for F.'gilli control. RESULTS This study explored the RNAi functionality in F.'gilli using three main delivery methods: injection, soaking, and oral delivery. The aCOP, an essential eukaryotic gene encoding for subunit alpha of coatomer protein complex-I, was targeted. All delivery methods triggered RNAi response measured through a reduction in target gene transcripts; however, RNAi efficacy varied among the three methods. Injection demonstrated superior efficacy, achieving a 76% reduction in transcript levels. By contrast, the soaking delivery exhibited lower efficacy, resulting in a 27% decrease in transcript levels. Owing to its field relevance, the oral delivery employed through the topical-feeding method was standardized and optimized for both nymph and adult stages. Topical-feeding of target gene double-stranded RNA resulted in a reduction in transcript levels as high as 65% and a stage-specific phenotypic response, with a significant reduction in nymphal survival but no impact on adult survival. CONCLUSION Our research demonstrates conclusively that RNAi functions effectively in F.'gilli. Successful gene silencing observed via oral delivery supports developing the RNAi for field control of F.'gilli. Furthermore, the topical-feeding delivery method established here can be adopted for large-scale gene discovery in subsequent field evaluation.