NUTRITION OF THE PALE WESTERN CUTWORM, AGROTIS ORTHOGONIA MORR. (LEPIDOPTERA: NOCTUIDAE): II. DRY MATTER AND NITROGEN ECONOMY OF LARVAE FED ON SPROUTS OF A HARD RED SPRING AND A DURUM WHEAT

Abstract

Dry matter and nitrogen balances, determined for individual instars of the pale western cutworm fed ad libitum on wheat sprouts, showed that reliable data were obtained for only the fourth, fifth, and sixth instars. During the larval period a single cutworm consumed about 10 g of fresh wheat sprouts containing about 25 mg of nitrogen. Of the consumed food, 40–50% of the dry matter and 60–70% of the nitrogen were excreted. Five days after the fifth molt the fresh weights of larvae fed on sprouts of durum wheat were significantly less than those fed on sprouts of the hard red spring wheat, but the dry weights were the same. The quantities of nitrogen found in excreta and body tissue approximated that consumed by the larvae. In contrast, however, much of the consumed dry matter (14–33%) could not be accounted for; recovery varied with variety. The percentage of the dry matter utilized, about 50%, remained constant during the last three instars. Nitrogen utilization by fourth-, fifth-, and sixth-instar larvae ranged between 25 and 45%. However, a consistently lower percentage of the nitrogen was utilized from Thatcher than from Golden Ball sprouts. On both varieties the lowest values were obtained in the sixth instar. In the excreta the percentages of insoluble dry matter, insoluble nitrogen, and volatile bases showed no consistent change during the last four instars. Seventy to eighty per cent of the excreted nitrogen was soluble in 80% ethanol, and about one-fifth of this was in the form of volatile bases. The variety of wheat sprouts fed had little, if any, effect on the composition of the excreta.