Degree

Doctor of Entomology (PENTM)

Department

Entomology

Document Type

Dissertation

Abstract

The lesser grain borer, Rhyzopertha dominica, and the rice weevil, Sitophilus oryzae, are two of the most destructive pests of stored rice. Their management has relied heavily upon fumigant insecticides. However, amid growing concerns that fumigant-resistant pests are becoming widespread, there is an urgent need for diversified management techniques and integrated pest management. Here, we explored management techniques and the behavior of these beetles. Host plant resistance toward both beetles was evaluated for 13 varieties of rice. We found large differences among varieties for both beetles in all resistance measures. We found that while nutritional components of a variety did not influence resistance, grain dimensions did influence susceptibility to damage by R. dominica adults, larval damage, progeny counts, and progeny mass. Insecticide efficacy was examined by evaluating methoprene, deltamethrin, commercial formulations of methoprene + deltamethrin, β-cyfluthrin, and diatomaceous earth applied to rough rice over six-month periods. We found that methoprene, or a combination of methoprene and deltamethrin were the most effective controls of stored rice pests. Beauveria bassiana (strain: GHA) and Cordyceps fumosorosea (strain: FE9901) were evaluated as biological control agents of stored grain beetles, alone, together, and in combination with each other. There were higher infection rates of B. bassiana in the presence of diatomaceous earth than without it, while combinations of B. bassiana and C. fumosorosea sometimes resulted in antagonism. Finally, R. dominica and S. oryzae host-finding abilities were examined through their behavioral responses to different conditions of stored rice using a two-choice olfactometer. We compared responses to clean rice, damaged rice, conspecifics only, only damaged rice, rice infested with conspecifics, and rice infested by another species. While S. oryzae did not distinguish between most treatments, R. dominica preferred infested rice to only damaged rice or only beetles. Volatile profiles built through gas chromatography–mass spectrometry identified 8 volatiles unique between the R. dominica infested rice, beetles only, and damage only treatments that may have acted as attractants or deterrents. Taken together, these findings build a foundation for effective and sustainable stored grain pest management.

Date

10-29-2023

Committee Chair

Wilson, Blake

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Included in

Entomology Commons

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