Toxicity and repellent activity of a carlina oxide nanoemulsion toward the South American tomato pinworm, Tuta absoluta

Abstract

Plant essential oil (EO)-based insecticides represent a promising tool for Integrated Pest Management (IPM), though their formulation is limited by poor physicochemical properties. EO encapsulation into stable formulations, like nanoemulsions (NEs), could boost EO efficacy and stability. Carlina acaulis L. roots contain an EO recently studied for its excellent insecticidal activities, and chiefly composed of carlina oxide (> 97%). Herein, we developed two carlina oxide NEs (0.25% and 0.5% w/w) through ultrasounds exposure and characterized them by dynamic light scattering (DLS). The NE insecticidal and repellent activities were tested on Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae) eggs, larvae, and adults. Nanoemulsions tested showed a monomodal size ditribution and the polydispersity index (PDI) indicaticating a low grade of polydispersity. The 0.25% (w/w) NE showed significant contact toxicity on T. absoluta eggs with high hatching inhibition. 11 days post-treatment. The highest larvicidal effect was observed in translaminar toxicity tests, with complete mortality after 24 h. The NE did not achieve significant oviposition deterrence. Overall, the tested green NE showed promising effectiveness as ovicide and larvicide on T. absoluta, highlighting the need of further research to shed light on its modes of action, as well as to evaluate lethal and sublethal effects on tomato biological control agents and pollinators.