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

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 efficacy of four commercially available grain protectants, Gravista^® (deltamethrin + methoprene + PBO), Diacon^® IGR (methoprene), Sensat^TM (spinosad), and EverGreen^® (pyrethrin), applied to sorghum and held for 28 weeks, against <i>Rhyzopertha dominica</i> (F.) and <i>Sitophilus oryzae</i> (L.). Subsamples were collected every four weeks and infested with 10 adults of either species. Adult mortality was assessed after seven days and progeny, frass, and insect-damaged kernels were evaluated after eight weeks. <i>Rhyzopertha dominica</i> was more susceptible to all insecticides compared to <i>S. oryzae</i>, and had fewer progeny compared to control sorghum. Spinosad-treated sorghum resulted in 100% adult mortality in <i>R. dominica</i> compared to 30-39% in <i>S. oryzae.</i> 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 the influence of insecticide formulation, insect species, and grain moisture content on the long-term efficacy of grain protectants applied to sorghum.