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

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 (i) the fitness of S. oryzae, and (ii) 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 dataloggers were placed in the masses to record temperature and relative humidity every 5 min. After 60 d, progeny were counted, and grain moisture was also measured. Although mean temperature was not consistently altered in the presence of A. flavus or S. oryzae, the combined inoculation of A. flavus and S. oryzae in a grain mass consistently elevated relative humidity by 7% to 8%. The presence of A. flavus or S. oryzae consistently elevated grain moisture from 10.8% prior to the experiment to about 13%. 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, possibly indicating a mutualistic relationship. Our work adds to the growing body of literature suggesting that insects and microbes should be managed in concert at food facilities.