Integrated post-harvest management of stored product insects in sorghum: Effects of kernel properties, temperature, and grain protectant efficacy

Abstract

Sorghum bicolor, commonly known as sorghum, is one of the five most economically important cereal grains in the world. In the United States, it is used extensively for livestock feed and ethanol production, while globally, it serves as a staple food for >500 million people. Its value lies in part in its exceptional drought tolerance, enabling it to perform in regions where other cereals often fail. This resilience is largely due to sorghum’s genetic flexibility, which allows breeders to improve both agronomic performance and grain quality. Through targeted breeding, traits such as drought resistance, kernel hardness, protein content, starch composition, and kernel size can be selected, influencing sorghum’s suitability for various end uses. As global temperatures rise and water availability becomes increasingly scarce, sorghum’s role as a climate-resilient crop is expected to grow. However, post-harvest storage remains a critical challenge as arthropod pests reduce grain quality and quantity through direct feeding and contamination with frass, exuviae, webbing, and associated microbial growth. Key pest species, Rhyzopertha dominica, Sitophilus oryzae, Plodia interpunctella, and Prostephanus truncatus, cause substantial annual losses worldwide. To mitigate these losses during bulk storage, strategies such as sanitation, grain aeration, fumigation and the use of grain protectants are commonly employed. While the efficacy of grain protectants has been well studied in other cereal crops like wheat, rice, and maize, relatively little is known about their performance on sorghum. Integrated Pest Management (IPM) emphasizes the importance of understanding how grain traits, storage conditions, and pest biology interact to influence both stored product susceptibility and grain protectant efficacy. This research applied IPM principles to evaluate post-harvest protection of stored sorghum. First, we assessed the susceptibility of sorghum varieties differing in kernel hardness and protein content to infestation by R. dominica and S. oryzae. Results showed that both kernel hardness and protein content significantly influenced susceptibility to S. oryzae, while only protein content affected susceptibility to R. dominica. Second, we examined how storage temperature (22, 27, and 32°C) impacted the efficacy of four commercially available grain protectants (Diacon® IGR, EverGreen®, Gravista®, and Sensat™) against R. dominica, S. oryzae, and P. interpunctella, as well as its influence on pest development. We found that temperature had a significant effect on the grain protectant efficacy, with some formulations exhibiting a decrease or increase in their ability to mitigate infestation depending on environmental conditions. For instance, we found that insecticide formulations containing pyrethrins or pyrethroids performed better than cooler temperatures in terms of adult mortality and mitigating progeny and further damage, whereas there was an observed decrease in efficacy when temperatures were higher. The opposite trend was observed for the active ingredient spinosad, which saw a higher rate of efficacy at warmer temperatures and less efficacy at cooler temperatures. Overall, species development was faster at higher temperatures regardless of treatment. Third, we evaluated the long-term efficacy of the same grain protectants over a 28-week simulated storage period against R. dominica and S. oryzae. The grain protectant performance remained consistent over time, with high rates of adult mortality, low progeny, and lower levels of product damage observed for all protectants against R. dominica during the course of the experiment. However, the declining moisture content of the stored sorghum over time was a major contributing factor affecting infestation levels. Furthermore, R. dominica showed a higher degree of susceptibility to treated sorghum compared to S. oryzae. The results of these three studies support the need for the development of a sorghum-specific IPM strategies. The factors of grain varietal traits, grain protectant formulation, and storage environments all play a pivotal role in sorghum’s susceptibility to infestation of four primary species that infest bulk grain. Furthermore, this research highlights the importance of understanding the target-species biology and ecology when employing IPM strategies. Ultimately, this research lays the groundwork for understanding the challenges and opportunities for targeted post-harvest IPM practices in the United States and internationally.