Season-long microbial dynamics from the cuticle of rice weevil originating at food facilities after dispersal to novel food patches

Authors: Morrison, William - Rob; Ponce Jr, Marco; CASTALDI, DANTE - Kansas State University; JAMES, AVERY - Kansas State University; STOLL, IAN - University Of Missouri; MORELAND, JENNA - Kansas State University; Abshire, Jennifer; KIM, TANIA - Kansas State University; Gerken, Alison

Submitted to: Environmental Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/16/2024
Publication Date: N/A
Citation: N/A

Interpretive Summary: Stored product insects pose food safety concerns due to their capacity to vector microbes, which can potentially contaminate food consumed by humans or animals. We are unsure how environmental factors, such as temperature and time of year, influence the vectoring ability of stored product insects. Rice weevils collected from a grain storage location regularly over the course of a growing season, were allowed to walk on potato dextrose agar plates (a commonly used substrate for the growth of bacteria and fungi) and the subsequent coverage of the plates by microorganisms was measured. The greatest microbial growth consistently occurred from rice weevil collected during the wheat and maize harvest, while microbial richness, measured based on observed morphological and color differences in microbial colonies on plates, increased progressively over the growing season. We found there was greater microbial growth with increasing temperature in the field. This study highlights the ability of the rice weevil to vector microorganisms that might contribute to loses in grain quality during storage and identifies key times during the growing season when risk of microbial contamination from stored product insects is highest. As climate change progresses, the propensity for vectoring may be worsened by increasing temperature.

Technical Abstract: Stored product insects pose food safety concerns due to their capacity to vector microbes. As climate change progresses, the propensity for vectoring may be affected by temperature or other factors. Vectoring capacity may also possibly fluctuate over the course of a season. Thus, we evaluated 1) how the microbial growth and morphospecies richness vary over the growing season from field-collected S. oryzae and allowed to disperse onto a novel food patch of potato dextrose agar and 2) whether temperature in the week preceding collection of S. oryzae affected either response. On a weekly basis during 2022 and 2023, we introduced S. oryzae onto agar, and photographed patches at 3 and 5 d afterwards, characterizing growth with ImageJ and richness visually. There was 1.4–1.6 more microbial growth in patches at 5 d compared to 3 d in both years. The greatest microbial growth consistently occurred from S. oryzae collected during the wheat and maize harvest in the field, while morphospecies richness increased progressively over the season. We observed an 11-fold and 3-fold increase in the number of morphospecies at the end of the season compared to the beginning. There was 2.1- to 316-fold more microbial growth during the wheat and maize harvest, respectively, compared to the beginning of the season. We found a positive exponential relationship between temperature in the field and microbial growth in both years. This study expands our fundamental understanding of insect-microbe interactions after harvest and highlights variable periods of risk by food facilities over the season.