Synergetic enhancement of insecticidal efficacy of graphene with spinosad against major stored grain insects

Abstract

Pest resistance caused by repeated and excessive use of conventional pesticides has emerged as a significant challenge in modern agriculture, threatening global food security and the sustainability of agricultural practices. To address this challenging problem and shift away from dependence on chemical pesticides to more sustainable nanotechnology-based approaches, this paper presents a study exploring the combined use of graphene and biopesticide for advanced pest control. Naturally derived spinosad as a natural neurotoxin with lower resistance risks was combined with graphene-based nanopesticides offering efficient, and environmentally friendly pest control are explored to manage three key pests of stored products: Tribolium castaneum (Herbst), Oryzaephilus surinamensis (L.) and Rhyzopertha dominica (F.). The study assessed the insecticidal effectiveness of graphene (250 ppm), spinosad (200 and 400 ppm), and their combinations (250 ppm graphene + 200 ppm spinosad, and 250 ppm graphene + 400 ppm spinosad). Mortality rates were measured at 7-, 14-, and 21-days post-exposure, while progeny production was evaluated 65 days after treatment. Results indicated that the combination of graphene and spinosad significantly increased insect mortality across all three species when compared to either substance alone. Rhyzopertha dominica was the most susceptible in all spinosad treatments, both alone and in combination with graphene. Oryzaephilus surinamensis showed 97% mortality in graphene/200 spinosad, while T. castaneum, known for its tolerance to spinosad, showed lower mortality rates. Regarding progeny production, O. surinamensis exhibited zero progeny in all graphene-spinosad treatments, while R. dominica recorded complete inhibition of progeny in all treated groups. In contrast, T. castaneum showed fewer offspring compared to untreated controls. The increased efficacy of the graphene-spinosad combination appears to be due to graphene's ability to enhance contact with the insect cuticle, facilitating better penetration of spinosad and prolonging its insecticidal effects.