Injection, soaking, and oral delivery systems induce RNA interference-mediated silencing in the mealybug, Ferrisia...

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.

This study explored the RNAi functionality in F. gilli using three main delivery methods: injection, soaking, and oral delivery. The αCOP, 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.

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 for subsequent field evaluation. Published 2025. This article is a U.S. Government work and is in the public domain in the USA.