APPROXIMATE DIGESTIBILITY OF FIBER FOR A GRAMINIVOROUS CATERPILLAR

Final instar Persectania ewingii (Westwood) (Lepidoptera: Noctuidae) w ere fed seedling Triticum aestivum L. for 2 days to determine the appr oximate digestibility of the cell wall and cell content fractions. Cel l wall content was estimated using a micro-analytical neutral detergen t fibre technique. Approximate digestibilities of neutral detergent fi bre, neutral detergent solubles and dry matter were calculated for ind ividuals and pooled samples. P. ewingii larvae digested a small but si gnificant proportion of the fibre ingested (13-21%), higher than that previously reported for herbivorous insects. The micro-analytical and previously used macro-analytical techniques produced similar estimates of digestibility although both techniques have inherent shortcomings, the latter requiring the pooling of sampler and the former limiting t he number of replicates during chemical analysis. Differences in the a mount of larval frass collected during the feeding trial (corrected fo r consumption) explained much of the variation in digestibility values , while there were no effects of larval mass, overall consumption and total frass produced on digestibility estimates. These results confirm that plant cell contents are the major source of nutrients to larval Lepidoptera although there is some chemical disruption of the plant ce ll wall.