Oral delivery of dsRNA to Asian citrus psyllid, Diaphorina citri

Diaphorina citri Kuwayama (Hemiptera: Liviidae), also known as Asian citrus psyllid is one of the most important pests of citrus due to its role as a vector of the phloem-limited bacteria Candidatus Liberibacter asiaticus, the causal agent of the Huanglongbing (HLB) or citrus greening disease. The use of RNA interference (RNAi) as a biopesticide is rapidly becoming advanced tool in managing pests and arthropod vectors. Optimizing delivery and dose of dsRNA to different target organisms can present unique challenges.  In this study two oral delivery methods were tested for dsRNA designed to knock down Clathrin heavy chain (CHC) expression in nymphs and adults of D. citri given ingestion-access to: 1) 20% sucrose solution and 2) leaflets/cut stem of orange jasmine Murraya paniculata following dsRNA uptake from dsRNA-water solution at final concentration 100 ng. μL-1.  The qRT-PCR analysis confirmed dsRNA ingestion based on knockdown using both methods, which employed a 48-h dsRNA-access feeding and a three-day incubation-access period. Significant (p < 0.05) knockdown of CHC gene expression in D. citri was observed, ranging from 18–50%. The CHC expression was significantly reduced (p < 0.05) in D. citri following ingestion of dsRNA in a 20% sucrose solution, resulting in 50% and 30% knockdown for nymphal and adult stages, respectively. While nymphs and adults ingested dsRNA delivered via the orange jasmine plant system, gene expression was reduced by only 18 % in the nymphal stage.