In breeding corn varieties resistant to the corn borer, artificial infestation of test plants requires mass rearing of the insect in the laboratory. The mass rearing technique so far practiced in the Philippines uses expensive diets but results in low output.
　We tried to introduce and modify the rearing method established by Saito (1980) for the corn borer, Ostrinia furnacalis. The Saito diet was first modified by using soybean as a substitute for kidneybean, and again modified by using mung bean in place of soybean. Addition of sorbic acid, aureomycine and propionic acid was made. The modified diet containing mung bean allowed better growth of the corn borer and appreciable suppression of fungal occurrence. With this diet, a 30% reduction of the supply quantity was made possible without causing adverse effects on pupal growth and egg production. Covering each oviposition cage with a plastic sheet and supplying a foam mat soaked with water to the bottom of the cage enabled to produce an average of 12 egg masses per female, in contrast to the average of 3 egg masses per female, hitherto noted.
　Due to these improvements of the rearing method, the cost of the diet used for producing egg masses was reduced to only one-tenth that of the former rearing method.