Bombyx mori pylorus infection by Alphabaculovirus

Alphabaculovirus is an entomopathogenic virus genus that infects Bombyx mori, which is known as the Bombyx mori multiple nucleopolyedrovirus (BmMNPV). This virus is polyorganotrophic, and a series of tissues are known as targets; however, there is currently no information regarding infection in the pylorus, the segment of the hindgut that is present in the midgut transition and is responsible for food passage control. Thus, in the present study, we aimed to analyze infection of the B. mori pylorus by BmMNPV. To do so, hybrid B. mori larvae were inoculated with a viral suspension of BmMNPV, and segments of the intestine containing the pylorus and its subdivisions, the posterior interstitial ring (PIR), pyloric cone, and pyloric valve, were dissected and processed for light microscopy on different days post inoculation. The results showed that B. mori pylorus subdivisions respond differently to infection, and the anterior area of the PIR is susceptible with these cells being the secondary infection targets. Cytological analysis revealed the presence of viroplasm in the hypertrophic nucleus, followed by the formation and development of viral polyhedra. Cytolysis occurred at the end of the infectious cycle, thereby releasing polyhedra and enabling the spread of the disease. There was no evidence of BmMNPV infection in the posterior area of the PIR, cone, or pyloric valve. These results will contribute to greater understanding of the virus infectious cycle, whose consequent epizootic disease can negatively impact this economically important insect that is used in silk production in Brazil.