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

The maize weevil (Sitophilus zeamais) is the most pestiferous insect of stored grains worldwide. The diet often influences various performance traits of insects, including the assembly of their gut microbiota. In this work, we reared S. zeamais on maize, wheat, or barley grains and evaluated its impact on the assembly of the gut microbiota and different population traits. We found important adjustments to the assembly of maize, barley, and wheat. We found that the structure of the bacterial community in the maize diet (with dominance of Chitinophaga, Paracoccus, Sphingobacterium, Acinetobacter, and Brucella) differed from those of barley and wheat, which shared dominance of the genera Gluconobacter, Cetobacterium, and Rickettsia. We also found significantly different genera depending on the grain type. In maize, we found an enrichment of Acinetobacter and Comamonas; in the wheat diet, we detected Gluconobacter, Cetobacterium, and Chroococcidiopsus, while in barley, we only detected the enrichment of Staphylococcus. Maize significantly promoted the longest longevity, the longest oviposition period, and the biggest and heaviest offspring. In contrast, wheat and barley produced the largest number of 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 the carrying capacity of the grains, the putative role of phylosymbiotic endophytes associated with the seeds, and the nutritional differences in each diet type.