Abstract: The origin of the chief cellulose digesting enzyme, C_X-Cellulase, in longhorn beetles was investigated. Homogenate of alimentary canals of 18 species of female adults, 16 species of male adults and 12 species of larvae of two subfamilies (Lamiinae and Cerambycinae) were tested with the isoelectric-focusing PAGE method.The zymograms of cellulase isozymes were quite different in various developmental stages and larval instars. The origin of C_X-Cellulase in digestive tract (mid-gut, hind-gut) of cerambycid beetles was discussed in detail.The author inclined to draw a conclusion that most species of cerambycid beetles are able to secrete their own C_X-Cellulase.

Key words: C_x-Cellulase, Cerambycidae