Changes in urea in the haemolymph of the silkworm, bombyx mori in the fourth and the fifth larval instars and effect of starvation in th fifth instar on the level of urea in the pharate adults

Abstract

1. 1. Urea in the haemolymph was determined during the development in the silkworms, Bombyx mori that were reared on artificial diet and on fresh mulberry leaves. 2. 2. In the fourth and the fifth larval instars, the changing pattern and the level of urea were similar in the silkworms reared on artificial diet and on fresh mulberry leaves. A peak of concentration of urea, approx. 0.7 mg urea N/ml, was observed in each instar. These were the new observations. 3. 3. In the pharate adult development, a high level of urea, a maximum of approx. 1.0 mg urea N/ml, was observed in the silkworms reared on artificial diet and a low level, approx. 0.05 mg urea N/ml, was observed in the silkworms reared on fresh mulberry leaves. These results were similar to the reported results (Inokuchi et al., 1983 Appl. Ent. Zool. 27, 99–105). 4. 4. In the fifth larval instar, starvation experiments were carried out, beginning from 48, 72 and 96 hr after the fourth larval-larval ecdysis in the silkworms reared on fresh mulberry leaves. 5. 5. Starvation from 72 hr let the silkworm larvae transform themselves to pharate adults and produced a changing pattern of urea in the pharate adult that is closely similar to the changes in the silkworms reared on artificial diet only. This result might support the hypothesis (Yamada et ai, 1984 Appl. Em. Zool. 28, 49–56) that urease in mulberry leaves enters into the haemolymph in the mature larvae through the midgut tissue in the fifth instar.