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

Abstract

Stored-product insects may pose food safety concerns due to their capacity to vector harmful microbes. As climate change progresses, the propensity for vectoring may be affected by temperature. Vectoring capacity may also fluctuate over the season. Thus, we evaluated (i) how the area of microbial growth and morphospecies richness vary over the season from field-collected Sitophilus oryzae that were allowed to disperse onto a novel food patch habitat comprised of agar and (ii) whether temperature in the week preceding collection of S. oryzae affected growth and richness. On a weekly basis during 2022 and 2023, we introduced S. oryzae onto agar, and photographed patches at 3 and 5 d, characterizing growth with ImageJ and visually scoring richness. There was 1.4- to 1.6-fold 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 grain bins, while morphospecies richness increased progressively over time. We observed an 11-fold and 3-fold increase in the number of morphospecies at the end of the season compared to the beginning in 2022 and 2023. There was 2.1- to 316-fold more microbial growth during the wheat (Jun to Jul) and maize harvest (Sep to Oct) compared to early May. We found a positive exponential relationship between temperature in the field and microbial growth in both years. This study expands our understanding of insect-microbe interactions after harvest and highlights variable periods of risk by food facilities over the season.