Date of Graduation

8-2023

Document Type

Thesis

Degree Name

Master of Science in Entomology (MS)

Degree Level

Graduate

Department

Entomology

Advisor/Mentor

Neelendra Joshi

Committee Member

Glenn Studenbaker

Second Committee Member

Ben Thrash

Third Committee Member

Nick Bateman

Abstract

Corn is an important cereal crop cultivated across various countries, including the United States. Corn serves multiple purposes such as human and livestock food and raw material for industrial processes. Despite being an important crop, corn production faces challenges due to factors such as weather fluctuations and the presence of insect pests and diseases, both in the field and during storage. Among these challenges, insect infestation poses a major threat, as the insect damage not only reduces the quantity and quality of the grain but also renders it unfit for human and animal consumption, leading to a decrease in market value. To address the challenges of insect infestation in stored grain, several control methods have been employed which include cleaning and drying grain to eliminate debris, the use of airtight containers or hermetic storage facilities, the application of botanicals with insecticidal properties, heat treatment, and the use of insecticide chemicals. Insecticides have been extensively used since 1950 to deal with various insect pests due to their effectiveness, ease of application, and long-lasting effects. This research examined the toxicity of four different insecticides namely, pirimiphos- methyl, deltamethrin, deltamethrin plus (S)-methoprene and malathion against Sitophilus oryzae, Tribolium castaneum, and Tribolium confusum infesting corn. The toxicity of each insecticide was determined in terms of LC50 by exposing target pests at different doses and the mortality was observed at 24 to 96 hours of exposure as well as until 10 days to determine delayed mortality. In the first study, the toxicity of the ementioned insecticides to S. oryzae was evaluated and the results revealed that pirimiphos-methyl insecticide was more toxic to S. oryzae, followed by malathion, deltamethrin, and deltamethrin plus (S)-methoprene. When the LC50 value of each insecticide formulation was compared with the label-recommended application rate, we found that only malathion was aligned with the label rate and did not need to be adjusted. Pirimiphos-methyl was over-applied, and the rate may be adjusted. In the second study, the toxicity of these insecticides was determined for T. castaneum and T. confusum. The results indicated that deltamethrin plus (S)-methoprene and deltamethrin displayed the highest toxicity against T. castaneum, followed by pirimiphos-methyl. Malathion displayed the lowest toxicity among all the insecticides tested. On the other hand, pirimiphos-methyl was highly toxic among all the insecticides, followed by deltamethrin plus (S)-methoprene, deltamethrin, and malathion against T. confusum. Although these two pests are closely related species, their susceptibility to the selected insecticides was different in such a way that T. confusum displayed higher susceptibility to pirimiphos-methyl compared to T. castaneum while T. castaneum exhibited greater susceptibility to deltamethrin, deltamethrin plus (S)-methoprene, and malathion compared to T. confusum. Compared the label recommended application rate with the LC50 found in the study, deltamethrin plus (S)-methoprene and malathion for T. confusum were appropriate and did not require any changes while the recommended label rate for pirimiphos-methyl exceeded the LC50 value for both species of flour beetles. These findings contribute to our understanding of insecticide toxicity to these stored-grain pests and provide valuable insights for their management.

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