Τowards an RNA-based biocontrol approach of olive fruit fly

Abstract: Olive fruit fly (Bactrocera oleae) is the most serious insect pest of olive (Olea europea) fruits in the world with causing severe crop yield and monetary losses. The control of B. oleae remains almost exclusively based on insecticides, an approach that is dangerous for the environment. Clearly, alternative approaches for olive fruit fly control are an urgent need. Exogenous RNA interference (exo-RNAi) is a promising tool in modern pest management which offers extreme specificity of action and minimal environmental risk (Dalakouras et al., 2020). RNAi is a conserved eukaryotic mechanism that is triggered by double stranded RNAs (dsRNAs) that are processed into 20-25-nt small RNAs (sRNAs) which target complementary mRNAs for degradation and/or translational arrest. Exogenous application in plants of such RNA molecules designed to target insect essential genes can be taken up by them and, ideally, lead to their lethality. In order to prove the concept and investigate whether sRNAs can indeed be applied in olive trees and transported to the fruits so as to be taken up by the B. oleae larvae, we introduced by trunk injection 22-nt sRNAs (chemically synthesized, CY3-labelled). Confocal microscopy revealed that the oligonucleotides were transported through the xylem to the fruits already 48 hrs post application and, importantly, taken up by the B. oleae larvae. Future studies optimizing formulation and delivery methods and selecting the most suitable gene targets should pave the way towards the development of novel RNA-based biocontrol compounds for olive fruit fly management.