Multiple infestation of a grain mass by Sitophilus oryzae L. (Coleoptera: Curculionidae) and the fungus, Aspergillus flavus, optimizes abiotic conditions for improved insect fitness

Authors: PONCE, MARCO - Orise Fellow; KIM, TANIA - Kansas State University; Morrison Iii, William

Submitted to: Environmental Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/21/2025
Publication Date: N/A
Citation: N/A

Interpretive Summary: Microbial contamination and damage from stored product insect feeding represent two of the leading causes of post-harvest losses to grain in bulk storage. Although either factor alone can cause substantial damage to bulk grain, insects and microbes often co-occur and may create environmental conditions that are mutually beneficial, compounding damage to stored grain. For example, microbial growth may increase temperature and relative humidity, which could promote insect population growth. The rice weevil, one of the most prominent pests of stored grain, is often closely associated with Aspergillus flavus, an important stored product fungus that produces carcinogenic mycotoxins. The goal of our study was to determine how A. flavus affected 1) the offspring produced by rice weevil, and 2) the environmental conditions in a grain mass. The presence of A. flavus in bulk grain increased rice weevil offspring production by over 200-fold. Although temperature was not majorly impacted much by rice weevil or A. flavus, relative humidity was consistently elevated by 7–8% when A. flavus was present. Our findings suggest that A. flavus can promote rice weevil population growth by creating favorable humidity conditions. Our work adds to the growing body of literature suggesting that insects and microbes should be managed in concert at food facilities.

Technical Abstract: Understanding the combined contribution of insects and microbes to conditions in a grain mass is particularly relevant for pest management programs in bulk storage. There are important and strong interactions between Sitophilus oryzae (L.) and stored product fungi, especially Aspergillus flavus (Link). The aims of this study were to determine how the introduction of S. oryzae, A. flavus, or both in a grain mass affected 1) the fitness of S. oryzae, and 2) the abiotic conditions in a grain mass. Containers with 300 g of wheat were established with no insects or added microbes, 75 mixed-sex S. oryzae adults only, 11.6 g of A. flavus-inoculated grain only, or both, and a datalogger was placed in the mass to record temperature and relative humidity every 5 min. After 60 d, progeny was counted, and grain moisture was also measured. After 20 d, the mean temperature decreased the most in the A. flavus, and A. flavus + S. oryzae treatment by 0.33 and 0.35°C, whereas in the last 20 d, the temperature increased by 0.15 and 0.03°C, respectively, compared to the controls. Combined inoculation of A. flavus and S. oryzae in a grain mass consistently elevated relative humidity by 7–8%. Importantly, there were 203-fold more F1 progeny produced by S. oryzae when A. flavus was present compared to when it was absent in a grain mass. Our work adds to the growing body of literature suggesting that insects and microbes should be managed in concert at food facilities.