Cellulolytic activity in a phytophagous lepidopteran insect Philosamia ricini: The origin of the enzymes

Abstract

The presence of cellulases in a phytophagous insect hitherto considered as devoid of any cellulolytic enzymes, has been reported for the first time in the phytophagous lepidopteran, the eri silkworm Philosamia ricini. Cellulose digestion in Philosamia ricini appears to occur independently of its gut flora and via enzymes synthesized by the insect itself. The failure of three wide spectrum antibiotics to induce any change in the cellulolytic activity in this insect at any stage of its development evinces the non-participation of its gut flora in cellulose digestion. Culturing the antibiotic-fed larval gut fluids in appropriate media revealed the ability of tetracycline to effect complete inactivation of all bacteria and fungi by day 4 whereas penicillin and streptomycin could achieve it only partially. The cellulolytic activity, however, in all insect groups remained unaffected. The suggests that it is the endogenous enzymes of P. ricini that catalyze cellulose hydrolysis. This has been further confirmed by long term feeding of antibiotics to the insects.