Invasive alien plant species aqueous extracts in a war against the granary weevil (Sitophilus granarius [L.]) – are they long-term effective or can they only win the Battle of Cannae?

This study investigates the effectiveness of plant-based extracts in repelling the granary weevil (Sitophilus granarius), a common storage pest causing significant economic losses. The selected plant species (Canadian goldenrod, giant goldenrod, indigo bush, staghorn sumac, and tree of heaven), were examined for their repellent effects on weevils in grain samples. Surprisingly, the short-term repellent effects observed after 24 h diminished after 3 days, suggesting potential challenges for practical applications, especially in long-term grain storage. Temperature emerged as a significant environmental factor, influencing weevil behavior. Lower temperatures created an illusion of increased effectiveness, while higher temperatures accelerated weevil reproduction. Commercial product NeemAzal, despite its reputation for effectiveness, proved the least potent among all treatments, raising questions about its applicability in such cases. Progeny emergence tests indicated no significant differences between treatments, emphasizing the ineffectiveness of the extracts in sustaining long-term repellent effects. The study concludes that while plant-based extracts may offer short-term victories in pest control, their long-term efficacy remains uncertain. The complex interplay of factors, including temperature and humidity, highlights the challenges in developing sustainable and practical solutions for grain storage pest control, necessitating careful consideration by real-world users.