Evaluating the Long-Term Efficacy of Four Active Ingredients against Rhyzopertha dominica (F.) (Coleoptera: Bostrichidae) and Sitophilus oryzae (L.) (Coleoptera: Curculionidae) on Stored Sorghum

Authors: LIBA, TANNER - Kansas State University; ZHU, KUN YAN - Kansas State University; Scheff, Deanna

Submitted to: Insects
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/27/2026
Publication Date: 3/3/2026
Citation: Liba, T., Zhu, K., Scheff, D.S. 2026. Evaluating the Long-Term Efficacy of Four Active Ingredients against Rhyzopertha dominica (F.) (Coleoptera: Bostrichidae) and Sitophilus oryzae (L.) (Coleoptera: Curculionidae) on Stored Sorghum. Insects. Insects 2026, 17, 273. https://doi.org/10.3390/insects17030273.
DOI: https://doi.org/10.3390/insects17030273

Interpretive Summary: Stored product pests such as the lesser grain borer and the rice weevil cause significant damage and losses in bulk grain storage globally. In the United States (US), grain protectants are commonly applied to grain prior to storage. However, the residual efficacy of grain protectants can be affected by environmental factors, commodities, and pest biology. The efficacy of grain protectants in long-term storage has not been adequately addressed. Our research group compared four commercially available sorghum grain protectants inside a grain bin over a 28-week period. The grain protectant Sensat, which contains spinosad, was most effective at controlling both species. However, the lesser grain borer was more susceptible to all the grain protectants with higher adult mortality and lower offspring production compared to the rice weevil. Moisture content also contributed to general decreases in insect population levels and feeding damage as moisture declined from 14 to < 9% over the course of the study. These results demonstrate that even though spinosad was effective, the efficacy varied between both species. The use of any formulation of grain protectant reduced insect populations and feeding damage compared to no treatment. Thus, the biology of the target pest should be considered when choosing a formulation of grain protectant to use on sorghum.

Technical Abstract: Grain protectants are insecticide formulations applied directly to raw grain to prevent and control insect infestations in bulk storage; however, their efficacy depends on insect species, commodity, and grain quality. The objective of this study was to determine the residual ef-ficacy of four commercially available grain protectants, Gravista® (deltamethrin + metho-prene + PBO), Diacon® IGR (methoprene), Sensat™ (spinosad), and EverGreen® (pyrethrin), applied to sorghum and held for 28-weeks, against Rhyzopertha dominica (F.) and Sitophilus oryzae (L.). Subsamples were collected every four weeks and infested with 10 adults of either species. Initial adult mortality was assessed after seven days and progeny, frass, and insect damaged kernels were evaluated after eight weeks. Rhyzopertha dominica was more suscep-tible to all insecticides compared to S. oryzae, and had few progeny compared to untreated sorghum. Spinosad treated sorghum resulted in 100% initial adult mortality in R. dominica compared to 30 – 39% in S. oryzae. There was an overall decline in kernel moisture content, which may have impacted progeny of both species in the control and insecticide treated sorghum. These findings highlight influence of insecticide formulation, species identifica-tion, and grain quality on the long-term efficacy of grain protectants applied to sorghum.