Insecticidal Characteristics and Mechanism of a Promising Natural Insecticide Against Saw-Toothed Grain Beetle

The prevention of grain storage pests is a universal concern all over the world. It is in high demand to explore novel, safe and green insecticidal techniques to address such concerns. In this work, both raw and calcined diatomite were used as a natural insecticide to remove common grain storage pests with improved lethal effect on the saw-toothed grain beetle. Interestingly, the raw diatomite showed higher insecticidal efficiency than the calcined diatomite, and its associated insecticidal properties and preparation conditions were also optimized through orthogonal tests. The optimal conditions for processing the raw diatomite insecticide were identified as follows: the diatomite dust was 500 mesh (A 3), the temperature was 25 °C (B 1), the relative humidity was 65% (C 2), the diatomite dosage was 20 g m-2 (D 2), the influence factor order was C ≥ D > A > B. The observation of surface morphology indicated that the raw diatomite had a complete, multi hole surface morphology and good adsorption performance, whereas the structure of the calcined diatomite was uncomplete with collapsed pores, resulting in poor adsorption performance. The special pore structure and excellent adsorption capacity of diatomite make the stored grain pests lose water to lethal effect. Acute toxicity and long-term toxicity tests in mice showed that diatomite has no harmful effects on mammals. The findings from our work led to a green and effective approach in producing a highly efficient and safe storage grain insecticide.