Entomopathogenic fungi as biological control agents of beetle pests in stored rice

Across the world, 5–30% of stored rice value is lost postharvest due to insects. The lesser grain borer, Rhyzopertha dominica, and the rice weevil, Sitophilus oryzae, are two of the most damaging pests of stored grain. They are invasive in United States and are globally distributed, threatening rice postharvest worldwide. Current management tactics rely heavily on fumigant insecticides, but with some fumigants being phased-out, and insecticide-resistant populations of these pests appearing in places across the world, integrated pest management is needed. The entomopathogenic fungi Beauveria bassiana and Cordyceps fumosorosea have shown promise as alternative pest management tactics. However, much of the research has been done within stored wheat using field collected fungal strains. Commercially-available strains of fungi have yet to be evaluated for these pests, and evaluations within stored rice are lacking. Here, we assess the efficacy of Beauveria bassiana GHA and Cordyceps fumosorosea FE9901 against lesser grain borers and rice weevils within stored rice. Both fungal strains were tested individually, in combination, and with diatomaceous earth to determine potential synergetic interactions. The effects of fungal infection upon beetle behavior were also examined. Specifically, changes in locomotion, feeding, grooming, and mating were studied to gain a better understanding of pest immune response and fungal transmission mechanisms. Our results will improve the sustainability of rice storage by developing integrated pest management approaches that reduce reliance on fumigation, reduce production costs, and increase understanding of the factors influencing stored rice pest population dynamics.