Developing green insecticides to manage olive fruit flies? Ingestion toxicity of four essential oils in protein baits on Bactrocera oleae

Effective and eco-friendly plant-borne insecticides for developing lure and kill control tools against tephritid flies are scarce. Herein, the activity of four essential oils (EOs) obtained from two Apiaceae, Pimpinella anisum L. and Trachyspermum ammi (L.) Sprague, and two Lamiaceae, Thymbra spicata L. and Ocimum gratissimum L., was evaluated against the olive fruit fly, Bactrocera oleae (Rossi), a key pest of olive groves. The EO chemical composition was determined by gas chromatography coupled with mass spectrometry (GC-MS) analyses. The four EOs incorporated in protein baits were tested for ingestion toxicity on B. oleae adults, mimicking lure and kill assays. Results showed concentration-dependent toxicity, with mortality rates ranging from 6.5% (P. anisum EO at 0.03% w/v concentration) to 100% (P. anisum EO at 0.5% w/v concentration, T. ammi EO at 1% w/v). The best efficacy was achieved by EOs from T. ammi and P. anisum, showing LC50 values of 633 ppm and 771 ppm, respectively, far encompassing currently published findings on the ingestion toxicity of EOs on tephritid adults. Thymol (58.3%), p-cymene (24.7%) and γ-terpinene (14.2%), and (E)-anethole (98.3%) were the major constituents of T. ammi and P. anisum EOs, respectively. Thymol (57.0%), p-cymene (12.4%) and γ-terpinene (6.9%), and carvacrol (41.4%) and p-cymene (41.2%) were the predominant components in O. gratissimum and Th. spicata EOs, respectively. Further field research on the efficacy of these EOs incorporated in food baits against the olive fruit fly is ongoing to boost their real-world application, contributing to develop alternative tools for the sustainable management of B. oleae.