Utilization of dry matter and elements by larvae of the sawflies Neodiprion sertifer (Geoff.) and Diprion similis (Hartig) feeding on Scots pine needles.
The consumption and proportions of dry matter and various elements utilized by late-instar larvae of Diprion similis and Neodiprion sertifer feeding on previous years' needles of Scots pine (Pinus sylvestris) were determined gravimetrically and by means of cellulose as an indigestible marker substance. The only discrepancy between the 2 methods was for phosphorus intake by females of N. sertifer. Female larvae of D. similis utilized larger proportions of dry matter, nitrogen and potassium, and less phosphorus than female larvae of N. sertifer; both species utilized similar proportions of calcium and magnesium. Combined male and female groups of larvae of N. sertifer utilized larger proportions of dry matter, potassium and magnesium compared with female larvae. The proportions utilized were ranked as follows: nitrogen (50-59%), phophorus (22-39%), magnesium (15-29%), calcium (9-15%) and potassium (6-17%). Non-positive sodium budgets precluded calculation of utilization of this element. The proportions of dry matter utilized by these sawflies were similar to those for 10 other species of foliage-consuming Hymenoptera, and fell towards the end of the range for phytophagous insects. Nitrogen utilization figures for these sawflies fell within the range of values reported for insects that consume tree foliage.