Nutritional Requirements of the Silkworm, Bombyx mori L.

Abstract

The nutrition of the silkworm, Bombyx mori L., has been of primary importance in sericulture, because not only larval growth and survival but also cocoon and egg production have been known to be influenced by the nutritive value of the foodstuff, mulberry leaves. The previous studies have been directed mainly at measur-ing the usefulness of the leaves or their specific components. This is, of course, one aspect of nutrition in animals which feed natural foodstuff, and the results so far obtained on the silkworm nutrition on this line are evaluated properly even now. However, no infor-mation has been available on the requirements for specific substances, either qualitatively or quantitatively, which enable the silkworm to grow and develop normally. In 1960 the rearing of the silkworm entirely on artificial diets has been reported for the first time.3),37>,43) Since then, the studies in our laboratory have been concerned with the elucidation of nutritional requirements of this insect, by means of artificial diets. The present report summarizes the results on the requirements for carbohydrates, amino acids, lipids, vitamins, and minerals. Nutritional tests were mostly carried out by rearing larvae on artificial diets, and the effects of supplementation or omission of specific substance on larval growth, development, and survival were carefully examined. Synthetic diet or amino-acid diet has success-fully been formulated for the nutritional tests.2°''23''26' When necessary, axenic rearing method was used.6',S)'26),39, Furthermore, enzymatic methods were used for the study of metabolic events on nutrients. Carbohydrates. The nutritive effects of carbohydrates were studied either by determining their effects on weight gain and survivall2),36),38) or by assaying the rate of conversion to blood trehalose or fat body glycogen,5''30' both of them occurring as main carbohy-drates in the body, when each compound was administered orally to the larvae without any other nutrient. Since some of sugars possess a strong phagostimulating action for silkworm larvae,13' it was afraid to get a misleading result when synthetic diets con-taining different sugars were compared. Similar to other species 58 T. ITO [Vol. 43, of insects, silkworm larva did not show any specific requirements for carbohydrates, although several compounds were utilized more readily than others. In general, pentoses were poorly utilized. Of hexoses tested, glucose, fructose, and mannose were utilized well. Disaccharides, especially sucrose, cellobiose, and maltose, were uni-formly good.