Sweet Fennel Essential Oil Repels Drosophila suzukii via an Orco-Mediated Pathway

Essential oils are promising alternatives to conventional chemical pesticides due to their toxic, repellent or oviposition-deterrent effects against many kinds of pests. Sweet fennel essential oil is widely recognized for its pharmacological, antimicrobial, and acaricidal properties. Moreover, several studies have demonstrated its insecticidal and repellent activities against insects. In this study, we found that sweet fennel essential oil exhibited strong dose-dependent repellent activity in the dual-choice still-air assay and oviposition behavioral assays against Drosophila suzukii adults. Next, we confirmed that trans-anethole was the most abundant constituent in sweet fennel essential oil using GC-MS. In addition, the results of the behavioral assays indicated that trans-anethole displayed comparable repellency against D. suzukii. Furthermore, an Orco knockout homozygous strain (Orco^-/-) was generated using CRISPR-Cas9 genome editing, and the EAG responses of Orco^-/- flies to sweet fennel oil and trans-anethole were completely abolished. The repellency elicited by sweet fennel oil and trans-anethole were also dramatically reduced. Taken together, these laboratory results not only reveal that sweet fennel oil holds potential in pest management but also demonstrate that its repellency is mediated by the Orco pathway.