As pointed out by the present authors (1962), digestion experiments on the silkworm by means of artificial diets are not only useful for the evaluation of efficiency of diets employed, but also very effective for the study of over-all utilization of food. It has been shown that the increase in the concentration of cellulose powder (C.P.) in artificial diets results in a marked acceleration of feeding (ITO, 1960, ITO et al., 1961) and eventually in a raise of the efficiency of diets. Since the silkworm does not digest cellulose, it has been concluded that C.P. must improve physical condition of diets. The present paper deals with the effect of C.P. on over-all utilization of artificial diets.
The main difference between five diets listed in Table 1 is varying concentrations of C.P. Among A, B, and C diets the corresponding amount of glucose plus soybean casein (keeping the ratio of glucose vs. soybean casein 1: 2) was subtracted, when increasing the amount of C.P. Among A, D, and E diets all of the ingredients except for C.P.(B vitamins added always constant) were included by keeping their mutual adding ratio constant, when changing the amount of C.P. The experimental larvae were reared, from hatching through the time when used, only on artificial diets.
1) When the concentration of C.P. increased, a rapid increase in body weight was obtained, and larval development was somewhat improved (Figs. 1 and 2).
2) It is evident from Table 2 that a sufficient amount of the food was supplied in the present experiment. The quantity of dry matter consumed was markedly increased according to increasing concentration of C.P. from 20 to 50%(Figs. 1 and 2, Table 2). No specific relation was found between total dry matter digested and the concentration of C.P. The coefficient of digestibility was high at a low concentration of C.P., while low at a high concentration of C.P.
3) Total dry matter of feces produced was increased when the concentration of C.P. increased. The increase in total dry feces was due to both the increase in the number of total fecal pellets and the increase in average dry weight of single fecal pellet (Table 3). However, the number of fecal pellets per g of dry matter consumed did not largely differ, even when C.P. concentration varied. The correlation coefficients showing the relationship between the amount (dry wt.) of foodconsumed and the number of fecal pellets, calculated from Tables 2 and 3, were highly significant; +0.974 (α=0.05) with the 3rd instar, 0.995 (α=0.01) and+0.982 (α=0.05) with the 4th instar, and +0.996 (α=0.01) with the 5th instar.
4) Since the silkworm does not digest cellulose, dry matter of the food digested is considered not to contain any cellulose powder. Calculations were made on the data of Table 2, and dry matter consumed as well as coefficient of digestibility were obtained with the part of diet without C.P.(Table 4). Thus, so far as the part of diet without C.P. is concerned, there was rather little difference in both dry matter consumed and coefficient of digestibility according to different concentrations of C.P.
5) When the concentration of C.P. increased, more dry matter was necessary to be consumed for the gain of unit body weight, while less part of dry matter without C.P.(both consumption and digestion) is enough for it (Table 5). This fact seems to explain the reason of the increase in the efficiency of diet caused by the increase in C.P. of the diet.