Synergistically Better than One: Co-Application of Grasshopper-Derived +ssRNA Virus and Imidacloprid Induces Acute Toxicity in Locusta migratoria

Entomopathogenic viruses offer an eco-friendly biological approach for pest control, but their relatively slow action often limits practical applications. Synergistic interactions between insect viruses and chemical pesticides can amplify their control efficacy, reduce insecticide use, and thus alleviate associated risks. Here, we evaluated the combined effects of the gomphocerinae permutotetra-like virus (GPV) and the neurotoxic insecticide imidacloprid against nymphs of Locusta migratoria. In toxicity tests, neither GPV nor imidacloprid alone caused mortality from acute toxicity after 12 h (<30%), but co-application led to marked acute synergistic toxicity, significantly increasing mortality to 87% within 12 h and 93% by 96 h. Importantly, histopathological examination revealed that the synergistic treatment caused severe midgut damage, such as disrupted or absent microvilli, extensive cellular debris in the gut lumen, cell detachment from the basal lamina, and apical displacement of nuclei. Furthermore, RNA-seq and biochemical analyses showed that the cotreatment aberrantly regulated key genes involved in peritrophic membrane integrity, substantially elevated immune responses, and disrupted energy homeostasis, which collectively led to death. These critical insights on the mechanisms underpinning the synergistic action of viral and traditional chemical agents underscore the potential of such integrated strategies to rapidly, effectively, and safely control pests.