Evaluating the combination of Metarhizium anisopliae and an enhanced form of diatomaceous earth (Grain-Guard) for the environmentally friendly control of stored grain pests

Stored grain pests cause great damage to various grain products, and protection against these pests is currently based on synthetic insecticides and fumigants. As a result, these chemicals cause problems, including grain contamination with chemical residues and the development of resistance by insect pests to these chemicals. Therefore, to combat this issue, in the present study, an enhanced form of diatomaceous earth (DE), Grain-Guard, and Metarhizium anisopliae (Metschnikoff) Sorokin (Ascomycota: Sordariomycetes) were evaluated alone and in combination against adults of Liposcelis paeta (Pearman) (Psocoptera: Liposcelididae), Cryptolestes ferrugineus (Stephens) (Coleoptera: Laemophloeidae), Rhyzopertha dominica (F.) (Coleoptera: Bostrychidae), and Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae). M. anisopliae was used at a rate of 1.7 × 10⁴ conidia kg⁻¹ grain alone as well as with two doses of DE (25 and 50 ppm) on wheat under different exposure time courses (4, 7, and 14 days). It is worth mentioning that the combination of M. anisopliae and DE was highly effective against the adults of L. paeta, C. ferrugineus, R. dominica, and T. castaneum after 14 days of exposure. When DE and M. anisopliae were applied alone, DE showed more effectiveness than fungal conidia. Progeny emergence was decreased when modified DE was applied at a high dose rate with the fungus and suppressed at a low dose. The cadavers of all species in the trials showed a maximum percentage of mycosis, and sporulation (conidia/ml) also showed the same result when the fungus was tested alone, while low mycosis and sporulation were achieved under the application of a mixture with a high dose of modified DE. Our findings indicate the best possible combination of DE (at low dose rates) along with a fungus that might contribute to lowering health and environmental risks.