Cinnamomum camphora (L.) J. Presl. (Laurales: Lauraceae) is widely cultivated as an important landscape tree species in many urban areas in South China, especially in Shanghai City. Pagiophloeus tsushimanus Morimoto has become a destructive insect pest of C. camphora plantations in Shanghai, but the biological and ecological traits of this pest remain largely unknown. In this study, we investigated the damage and life history and determined the larval instar of P. tsushimanus. The results indicated that P. tsushimanus is a monophagous weevil pest, and C. camphora is the unique host tree species. C. camphora plantations in all administrative districts of Shanghai have been seriously damaged by P. tsushimanus. Adults often aggregate for feeding on the tender bark of twigs and occasionally on newly emerged buds. After experiencing damage, the twigs shrink and crack and the buds will shrink. Adults tend to repeatedly mate and oviposit, and all females lay single eggs at a time. Eggs will be covered with a mixture of secretions and wood chips by female adults. Larvae (1st–2nd instar) feed on the phloem, while 3rd–5th instar can bore into the phloem and the cambium. Massive tunnels, including three shapes (inverted “L”, inverted “T”, and inverted “Z”), were observed in the trunk of each tree, and resulted in swelling of the outer bark. P. tsushimanus has one life cycle per year in Shanghai. Both adults and larvae (3rd–5th instar) overwinter from early November to early April. Adults overwinter in grooves on the underside of branches or at branch nodes, and larvae overwinter in tunnels. Five larval instars of P. tsushimanus were determined according to Dyar's and Crosby's rules. The biological traits and life history of P. tsushimanus have been identified and can provide guidance in terms of pest control and plantation management.