Mechanism of the Change in the Intestinal Microbiota of C-Strain <i>Spodoptera frugiperda</i> (Lepidoptera: Noctuidae) after an Interspecific Transference between Rice and Corn

<i>Spodoptera frugiperda</i> (J.E.Smith) (Lepidoptera: Noctuidae) was first found in 2019 in Yunnan, China, and it was characterized as a corn strain; it was also found on rice strains there, and it damages rice in China, but little is known about the effect of host plant transfer on the intestinal microbiota and the activities of detoxification enzymes in the C-strain (corn strain) <i>S. frugiperda</i>. The intestinal microbiota and the protective enzyme activity of <i>S. frugiperda</i> that were transferred from rice plants were assessed, and the fourth generation of insects transferred from corn were studied; the gene types of <i>S. frugiperda</i> that were transferred from rice plants were tested using mitochondrial <i>Tpi</i> gene sequences. The results showed that the intestinal microbiota in the C-strain <i>S. frugiperda</i> were changed after the host transference, and the diversity and richness of the intestinal bacterial communities of the <i>S. frugiperda</i> feeding on rice were significantly reduced after the transfer of the host from corn. The predominant species of intestinal bacteria of the <i>S. frugiperda</i> on rice transferred from corn were <i>Enterococcus</i> and <i>Enterobacter</i>, with relative abundances of 28.7% and 66.68%; the predominant species of intestinal bacteria of the <i>S. frugiperda</i> that were transferred from rice and feeding on corn were <i>Enterococcus</i> (22.35%) and <i>Erysipelatoclostridium</i> (73.92%); and the predominant species of intestinal bacteria of <i>S. frugiperda</i> feeding on corn was <i>Enterococcus</i>, with a relative abundance of 61.26%. The CAT (catalase) activity of the <i>S. frugiperda</i> transferred from corn onto rice from corn was reduced, the POD (peroxidase) activity was significantly increased after the transfer from corn, and no significant variations were found for the SOD (superoxide dismutase), CarE (carboxylesterase), and GST (glutathione S-transferase) activities of <i>S. frugiperda</i> after the host plant transfer. The results showed that after feeding on rice, the activities of CAT and POD in the in <i>S. frugiperda</i> body changed in order to resist plant secondary metabolites from corn or rice, but there was no significant change in the detoxification enzymes in the body. In summary, switching the host plant between corn and rice induced variations in the intestinal microbiota in C-strain <i>S. frugiperda</i> owing to the strain difference between the C-strain and the R-strain (rice strain), and this was consistent with the results of the activities of detoxification enzymes. The results indicat that changes in intestinal microbiota and physiological enzymes may be important reasons for the adaptive capacity of C-strain <i>S. frugiperda</i> to rice.