Immune Gene Regulation In The Gut During Metamorphosis In Two Holo- Versus A Hemimetabolous Insect

During complete metamorphosis, holometabolous insects remodel their entire anatomy, including the gut and must control their microbiota to avoid infectious disease. High activity of antimicrobial peptides and proteins in the gut during metamorphosis has been best described in several Lepidoptera. The immune system of the dipteran Drosophila melanogaster also controls the number of bacteria during metamorphosis. However, little is known about the regulation of immune genes during the larval-adult moult in Hemimetabola which undergo less drastic metamorphic changes. Different patterns of immune effector expression during metamorphosis were shown in a study comparing the lepidopteran Galleria mellonela and the orthopteran Gryllus bimaculatus, where G. mellonella showed a strong up-regulation of antimicrobial peptides in the gut at the larval-pupal moult but not G. bimaculatus. Whether these findings reflect general patterns within holometabolous versus hemimetabolous insects remains unclear. Using RNAseq, we compare the expression of immune effector genes in the gut during metamorphosis in two holometabolous (Calliphora vicina and Tenebrio molitor) and a hemimetabolous insect (Pyrrhocoris apterus). We found high read count abundances of differentially expressed immune effectors in the gut at the larval-pupal moult in C. vicina and T. molitor; no such high abundances were observed at the larval-adult moult in P. apterus. Our findings confirm that only complete metamorphosis elicits a prophylactic immune response as an adaptive response in holometabolous insects, which controls the microbiota during gut replacement.