Grain type influences the assembly of the intestinal bacterial community and generates a fitness cost in the maize weevil, Sitophilus zeamais, Motschulsky 1855 (Coleoptera: Curculionidae)

The maize weevil (Sitophilus zeamais) is the most pestiferous insect of stored grains worldwide. In other insect species, it has been reported that diet often influences the assembly of their gut microbiota. In this work, we reared S. zeamais on maize, wheat, and barley grains. We evaluated its impact on the assembly of bacterial communities in the gut and some population traits in adult weevils. We observe that the structure of the bacterial community in maize grains (with dominance of Chitinophaga, Paracoccus, Sphingobacterium, Acinetobacter, and Brucella) differed from that of barley and wheat grains, which shared dominance of the genera Gluconobacter, Cetobacterium, and Rickettsia. We also found a significant enrichment of taxa depending on the grain type. In maize, we found an enrichment of Acinetobacter and Comamonas; in wheat, we detected Gluconobacter, Cetobacterium, and Chroococcidiopsus, while in barley, we only detected the enrichment of Staphylococcus. Weevils raised on maize had a higher parental longevity and oviposition time, as well as higher offspring weight and size. In contrast, wheat and barley promoted a larger offspring, with a sex ratio biased toward producing more males, but significantly smaller and lighter. The reasons behind these results are thoroughly discussed in terms of probably ecologically relevant factors such as the carrying capacity of the grains, the putative role of phyllosymbiotic endophytes of the seeds, and the nutritional differences in each diet type.