Piperitenone oxide-rich Mentha longifolia essential oil and its nanoemulsion to manage different developmental stages of insect and mite pests attacking stored wheat

Horsemint, Mentha longifolia (L.) Huds. (Lamiales: Lamiaceae), is a member of the genus Mentha, widely used for the repellent and insecticidal effectiveness of its essential oil (EO). Several chemotypes have been reported for this species. Here, we examined the efficacy of a M. longifolia EO, belonging to the piperitenone oxide-type, and a 10% (w/w) M. longifolia EO-based nanoemulsion (NE) as wheat protectants, at 500 and 1000 ppm of both the EO and the NE. The formulations were tested against four insect species and one mite species, i.e., the red flour beetle, Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae), the confused flour beetle, Tribolium confusum Jacquelin du Val (Coleoptera: Tenebrionidae), the yellow mealworm beetle, Tenebrio molitor (L.) (Coleoptera: Tenebrionidae), the saw-toothed grain beetle, Oryzaephilus surinamensis (L.) (Coleoptera: Silvanidae), and the flour mite, Acarus siro L. (Sarcoptiformes: Acaridae). The prepared NE showed a mean hydrodynamic diameter below 200 nm after preparation and no relevant changes in particle size distribution at least up to 4 months. The highest concentration of M. longifolia EO was the most effective grain protectant, causing 84.4 % and 100 % mortality to T. castaneum adults and larvae respectively, 42.2 % and 100 % mortality to T. confusum adults and larvae respectively, 100 % and 34.4 % to T. molitor adults and larvae respectively, 100 % for both adults and larvae of O. surinamensis, and 87.8 % and 67.8 % for the A. siro adults and nymphs respectively. Tribolium castaneum larvae were controlled by 500 ppm of the EO and 1000 ppm of the NE, which caused 100 % and 93.3% mortality, respectively. Similarly, 1000 ppm NE caused 96.7 % mortality against T. confusum larvae, while 500 ppm EO and 1000 ppm NE killed 90.0 % and 91.1% of T. molitor adults, respectively. Complete mortality (100 %) of O. surinamensis adults was achieved by 500 ppm EO. Our findings suggest that the M. longifolia EO and the M. longifolia EO-based NE may be considered as promising alternative wheat protectants against different insect and mite storage pests, depending on their developmental stage.