Insights into the seasonal ecology and thermal biology of the lesser grain borer, Rhyzopertha dominica (Coleoptera: Bostrichidae)

Abstract

Of the more than 20,000 edible plant species, maize, rice, and wheat provide half of the world’s diet. After harvest, these crops are stored for extended periods, but roughly 10 percent of global grain is lost to insect damage, costing the U.S. alone over 2.5 billion dollars annually. Among the estimated 1,500 insect species that can infest stored grain, the lesser grain borer, Rhyzopertha dominica, is a major pest capable of infesting intact kernels and causing damage directly or indirectly through contamination and promoting fungal growth. Its resilience to chemical controls and behavior of developing within grain kernels make traditional management challenging, prompting interest in alternative strategies such as cold-based interventions, including ambient and chilled aeration. Yet, the effectiveness of these methods depends on a variety of factors, including grain type, insect density, environmental conditions, and exposure duration. Here, our study addresses these knowledge gaps on how R. dominica responds to cold temperatures. A literature review first identified gaps in understanding how stored product insects tolerate cold conditions, with emphasis on R. dominica, and how this knowledge can reduce infestation risks under variable climates. Rhyzopertha dominica employs behavioral (e.g., burrowing, dispersal) and physiological (e.g., antifreeze proteins, cryoprotectants) strategies to survive harsh conditions. Commodity type and natural refugia further influence survival, and responses vary by insect species, sex, life stage, prior cold exposure, and population, highlighting the need for continued research on thermal biology to guide postharvest pest management. In line with understanding how cold treatments can be used to manage R. dominica, the first objective examined R. dominica habitats beyond stored grain, to see whether this species uses specific landscape features as alternative habitats. Field sampling in Manhattan, Kansas, indicated a strong association between beetle abundance and rodent dens. These data, combined with historical trap records, were used to develop predictive models of population trends across Kansas prairies. Incorporating climatic variables, forecasts suggest relatively stable populations through 2040, with slightly earlier seasonal emergence under warming scenarios, informing regionally adaptive monitoring and integrated pest management strategies. The second objective examined R. dominica movement under cold conditions, simulating navigation in grain bins or natural habitats. Beetles were tested across temperatures (10, 20, 30 C), acclimation (18 vs. 30 C), strains (lab colonies vs. recently collected, or wild), and sexes. Cold acclimation reduced movement at warmer temperatures but enhanced mobility in colder conditions. Females moved more than males, and lab strain beetles were more active than wild strain ones. These results indicate that acclimation, sex, and population origin strongly influence beetle movement and cold tolerance. The third objective examined how commodity type affects R. dominica survival and reproduction under warm and cold storage. Beetles were held in corn, sorghum, rice, or wheat at different temperatures (30, 18, or 5 C) for distinct exposure periods (2, 4, 8, or 12 weeks), then returned to 30 C for 6 weeks to simulate a recovery period from cold conditions. At 18 and 30 C, wheat, sorghum, and rice supported the highest adult counts, while corn was least favorable. At 5 C, counts across all grain types were relatively similar. Populations were highest at 30 C, intermediate at 18 C, and lowest at 5 °C. At 30 C, populations increased over time, stabilizing in sorghum, rice, and wheat, but continuing to rise in corn. Extended exposure at 18 C gradually reduced populations, while at 5 C, effects varied by commodity: corn and wheat remained stable at low levels, whereas rice and sorghum declined. These results indicate that even brief cold exposure (e.g., 4 weeks) can suppress reproduction, offering practical options for postharvest pest management. Overall, the work presented here emphasizes the complex interplay between thermal biology, behavioral ecology, commodity characteristics, and climate variability in shaping R. dominica population dynamics and responses to environmental stressors. Rhyzopertha dominica can withstand cold temperatures by seeking alternative habitats, acclimating gradually to cooler conditions, or persisting within the protective environment of grain. Integrating these factors into predictive models and pest management strategies will prove to be essential for optimizing cold-based interventions, enhancing sustainable grain storage, and mitigating economic losses under current and projected climate scenarios.