Cellulose content of food and faeces of Diprion similis as an internal marker for determining food consumption and digestibility

The consumption and digestibility of Scots pine (Pinus sylvestris L.) foliage by a diprionid sawfly (Diprion similis (Htg.)) can be determined indirectly by using the cellulose content of needles and faeces as an indigestible marker substance. No difference between figures obtained this way and those obtained by direct gravimetric determinations could be detected. This demonstration was preceded by exploratory studies to determine the feasibility of using lignin or cellulose content of the needles and faeces as the marker. Lignin was not employed because its methoxyl content decreases upon passage through the gut. By comparison with gas–liquid chromatography, the glucose oxidase (EC 1.1.3.4) method was shown to be satisfactory for the quantitative estimation of glucose in hydrolysates of cellulose isolated from needles and faeces.