There are a few papers reporting the rearing of the silkworm entirely on artificial diets, containing dried mulberry leaf powder at high concentrations such as 50% or higher than this. The present author has subsequently clarified several nutritive substances for the silkworm (ITO, 1961 a, b, c) and established physical conditions of diets required for better nutrition or feeding (ITO, HORIE, and TANAKA, 1961), by the use of artificial diets containing 10% leaf powder. On the basis of those findings, the rearing on artificial diets containing 10% leaf powder through all instars became possible (ITO, 1961 c). However, it has still been felt that further improvement is necessary possibly by reducing the amount of leaf powder until zero per cent or by replacing it with pure compounds.Recently an entire rearing on semi-synthetic diets, which did not include any leaf powder at all, was achieved. Though some improvement on such semi-synthetic diets is of course necessary, a short account about this will be made in the present paper.
The composition of semi-synthetic diets used for the present purpose is represented in Table 1. In formulating diets, previous results on nutritional requirements established already, not only qualitatively but also quantitatively, were taken into consideration. The methods of the preparation of diets and of rearing of larvae were similar to those previously described (ITO, 1961 a). Silkworm race was (J112×C110)×Daizo (the last one is multi-voltine race). The larvae were reared by means of Petri dish at 25°C throughout all instars.
The result of rearing is shown in Table 2. With diet A many larvae died by starvation in a few days after hatching and only 13 larvae survived after 7 days out of 40 newly hatched ones. Six larvae reached the fifth instar, two died during in this instar, and remaining four larvae made an extra molting to reach the 6th instar. Finally, one 6th instar larva started spinning after 40-day rearing and two larvae after 41-day rearing.
When diet B, the composition of which is somewhat different from that of diet A, was used, the larval development was recorded after 3-day rearing from hatching, considering a high mortality of newly hatched larvae caused by starvation. Larval development was much improved on diet B and one larva, not 6th but 5th instar, started spinning after 27-day rearing. The mortality by the end of the 4th instar was rather low, but some larvae died during the 5th instar.
Cocoons obtained were very white in color, since the diets did not contain any pigment precursors from mulberry leaves. However, the pigments contained in soybean casein and oil might color cocoons very faintly.
The result shown here is one of the instances of the rearing of the silkworm on semi-synthetic diets, and the rearing on other semi-synthetic diets of somewhat different composition has often been successful. The present diets do not contain any attractant so far reported, but some larvae grew well and made cocoons. The inclusion of attractant into semi-synthetic diets has recently been shown not to improve diet efficiency markedly (ITO and HORIE, 1962).
The present diets contained soybean oil, β-sitosterol, and ascorbic acid, all of which had been proved to be highly effective for silkworm nutrition (ITO, 1961 a, b, c), but at the same time it has been proved that all of them are more or less of phagostimulating action for the silkworm. ITo (1960) has previously emphasized the importance of “taste” in the mechanism of feeding reaction of the silkworm, and the present results confirm this obviously. Especially as for β-sitosterol and ascorbic acid, the present author considers them nutrients stimulating feeding simultaneously.
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