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

Plant essential oil (EO)-based insecticides represent a promising tool for IPM, though their formulation is limited by poor physio-chemical properties. EO encapsulation into stable formulations, like nanoemulsions (NEs), could boost EO efficacy and stability. Carlina acaulis roots contain an EO recently studied for its excellent insecticidal activities, and chiefly composed by 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. The NE insecticidal and repellent activities were tested on Tuta absoluta eggs, larvae, and adults. 0.25% and 0.5% NEs showed a monomodal size distribution with a Z-average size of 113.87±1.32 nm and 127.27±0.47 nm, respectively. The polydispersity indexes measured at 0.15±0.01 and 0.16±0.01 indicate a low grade of polydispersity. The 0.25% NE showed significant contact toxicity on T. absoluta eggs, with a maximum egg hatching inhibition of 85.7% 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 NE showed promising effectiveness as ovicide and larvicide on T. absoluta, highlighting the need of further research shedding light on its modes of action, as well as to evaluate lethal and sublethal effects on tomato biological control agents and pollinators.