The larvae of the rice stem borer, Chilo suppressalis WALKER, were reared on several artificial diets of different compositions under diapause-inducing condition (25°C and 12hr photoperiod). After 60 days of aseptic rearing, the larvae were kept at 8°C for 60 days, then they were incubated at 25°C for pupation. When the larvae were reared on diets containing rice bran or rice germ seedlings, most of the larvae survived after low temperature treatment. On the other hand, if the larvae were reared on four other kinds of diets which lack in plant materials above-mentioned, 80% of larvae died during the course of low temperature treatment. The larval blood proteins are divided into three main protein bands by agar gel electrophoresis technique; that is, albumin and globulin bands moving to anode side and another globulin band moving to cathode side. Of these bands, the globulin band moving to cathode side was more clearly detected in the diapausing larvae which were reared on suitable diet than that of the larvae reared on unsuitable diet. Accordingly, the inspection of protein fractions of haemolymph by means of an electrophoresis technique seems to be very useful to approach nutritional studies in insects.