Volatile fatty acids and methane production in relation to anaerobic carbohydrate fermentation in Oryctes nasicornis larvae (Coleoptera: Scarabaeidae).
Abstract Physico-chemical investigations into the conditions of cellulose digestion by Oryctes nasicornis larvae show that the intestinal contents constitute a reducing alkaline medium. The mesenteron presents facultative conditions and high pH values whereas in the proctodeum anaerobiosis is strict and the pH approaches neutrality. No cellulase activity is detected either in the gut walls or the contents. Among the products of polysaccharide fermentation, volatile fatty acids (VFA) and methane are identified. The VFAs are 3 or 4 times more concentrated in the mesenteron than in the proctodeal dilation and acetic acid predominates. The VFAs, which are also present in the haemolymph, must cross the intestinal barrier. Methane formation takes place exclusively in the proctodeal dilation from which it is released to the exterior.