The present work demonstrates how important food quality is to an insect. When the dietary inadequacy in an artificial food was dilution of its nutrient content to 85, 70 and 50%, respectively, fifth-instar Celerio euphorbiae (Linnaeus) ate progressively more food but they gained no more body weight on one diet than on another. The rate of food intake depended on nutrient concentration. On all nutrient levels the larvae were about 20% efficient in converting the foodstuff into body material and the body content of protein did not differ significantly.

When the dietary inadequacy was immoderate proportions of several nutrients, the effects were not so clearly marked; nevertheless, the rate of food intake of the larvae could explain their body weight. The tendency seemed to be for the larvae to eat less and to gain less weight on the imbalanced diet than on an adequate diet. Moreover, conversion of foodstuff into body material did not seem as efficient on the imbalanced diet as on the control.

The ecological significance of food quality suggested by the first example is that the destructiveness of phytophagous insects, for example, may depend in part on the degree of succulence and corresponding nutrient concentration of food plant tissues; and by the second example, that perhaps nutritional imbalances may play a part in controlling the potential destructiveness of insect populations.