Biocidal efficacy of dilute essential oil-in-water emulsion adjuvants against spotted-wing drosophila, Drosophila suzukii.

Growing concerns over pesticide resistance, environmental impact, and human health risks have intensified the search for safer, more sustainable pest management solutions. Among the alternatives, essential oils (EOs) have gained attention for their biodegradability, low toxicity to humans, and suitability for use in organic production systems. This study explores the biocidal potential of dilute oil-in-water emulsions containing carvacrol and eugenol against the invasive fruit pest Spotted Wing Drosophila, Drosophila suzukii Matsumura, through laboratory and field assays. The result demonstrates that carvacrol at 1% (w/v) caused >87% corrected mortality in contact toxicity tests and reduced adult emergence from treated fruit to 0.8 ± 0.37 flies at 3 days after spraying (DAS), compared to 7.2 ± 1.32 in controls. In contrast, eugenol at 1% caused ∼39% total mortality and reduced emergence to 5.4 ± 1.33 flies at 3 DAS. Fumigation assays showed carvacrol at 80 µL induced 94.2 ± 3.76% mortality, while eugenol caused 22.5 ± 5.24% mortality at the same dose. Combining 1% EO with Entrust® enhanced efficacy, with carvacrol + Entrust® achieving >95% mortality by 48 h and reducing emergence to <4 flies at 10 DAS. Phytotoxicity was observed at EO concentrations ≥2%, especially for carvacrol. These findings highlight the potential of EO emulsions as dual-function agents, serving as both biopesticides and adjuvants, and their integration into sustainable pest control strategies.