Grain inoculated with different growth stages of the fungus, Aspergillus flavus, affect the close-range foraging behavior by a primary stored product pest, Sitophilus oryzae (Coleoptera: Curculionidae)

Authors: PONCE, MARCO - Kansas State University; LIZARRAGA, SANDRA - Vestaron Corporation; BRUCE, ALEXANDER - University Of Tennessee; KIM, TANIA - Kansas State University; Morrison, William - Rob

Submitted to: Chemoecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/2/2022
Publication Date: 8/14/2022
Citation: Ponce, M.A., Lizarraga, S., Bruce, A., Kim, T.N., Morrison III, W.R. 2022. Grain inoculated with different growth stages of the fungus, Aspergillus flavus, affect the close-range foraging behavior by a primary stored product pest, Sitophilus oryzae (Coleoptera: Curculionidae). Chemoecology. 51(5):927-939. https://doi.org/10.1093/ee/nvac061.
DOI: https://doi.org/10.1093/ee/nvac061

Interpretive Summary: Semiochemical-based, behaviorally-based management of stored product insects requires behaviorally-active compounds to manipulate pest populations. One understudied source of these compounds are microbes, which produce their own suite of compounds in grain. Although some research has investigated the interactions among stored product insects and microbes, little research has examined how specific fungal life stages (asexual or sexual) affect volatile compound emissions in grain and linked it to the behavior of a primary pest, in this case, the rice weevil. Using headspace collection coupled with chemical analysis, we found the sexual life stage of the fungus A. flavus had the most unique emissions of microbial volatiles compared to the asexual life stage and other grain treatments. This translated to a higher number of entries into small zones with kernels containing grain with the A. flavus sexual life stage, as well as a higher cumulative time spent in those zones by rice weevil in a video-tracking assay in comparison to the asexual life stage. While microbial volatiles were important for foraging at close-range, the release-recapture assay indicated that grain volatiles were more important for attraction at longer distances. Overall, this study enhances our understanding of how microbial volatiles affects the foraging ecology of a primary stored product insect, and how we might use microbial volatiles in behaviorally-based management for stored product insects.

Technical Abstract: Although some research has investigated the interactions among stored product insects and microbes, little research has examined how specific fungal life stages affect volatile emissions in grain and linked it to the behavior of Sitophilus oryzae, the cosmopolitan rice weevil. Thus, our goals were to 1) isolate, culture, and identify two fungal life stages of Aspergillus flavus, 2) characterize the volatile emissions from grain inoculated by each fungal morphotype, and 3) understand how MVOCs from each fungal morphotype affect foraging, attraction, and preference by S. oryzae. We hypothesized that the headspace blends would be unique among our treatments and that this will lead to preferential mobility by S. oryzae among treatments. Using headspace collection coupled with GC-MS, we found the sexual life stage of A. flavus had the most unique emissions of MVOCs compared to the other semiochemical treatments. This translated to a higher number of entries into small zones with kernels containing grain with the A. flavus sexual life stage, as well as a higher cumulative time spent in those zones by S. oryzae in a video-tracking assay in comparison to the asexual life stage. While MVOCs were important for foraging at close-range, the release-recapture assay indicated that grain volatiles were more important for attraction at longer distances. There was no significant preference between grain and MVOCs in a four-way olfactometer, but methodological limitations in this assay prevent broad interpretation. Overall, this study enhances our understanding of how MVOCs affects the foraging ecology of a primary stored product insect.