The review of literature showed that nutritional studies have been made on a number of insects rut that the phytophagous insects have largely remained neglected, there being very few examples of these insects having been successfully reared on synthetic diets. Stress has been laid upon the qualitative and quantitative formulation of synthetic diets containing the essential nutrients, the various substances necessary a.s feeding stimuli, and possessing an acceptable physical texture. The larva of a phytophagous insect, Pieris braesicae L., wns therefore selected ae the subject of the present investigations. It is a pest of economic importance almost all over the world, and has the advantage of being readily reared in the laboratory at all times of the year. A semi-synthetic diet was devised, the 'unknown' factor of which was cabbage leaf power, includoo in the diet after attempts to produce a purely synthetic diet hsd failed. A leaf p0vrder concentration of 2 grams per 25 grams of medium was the optimum required by the caterpillars. The nutritional value of various substances was assessed by inclusion in, or omission from, this basic diet. In the oase of sUgars, the effects of various pentoaes, hexoses, di-, tri-, and polysaccharides and also one of the sugar alcohols, mannitol, were examined. It was found that sucrose was a strong phagostimulant as well as apparently being nutritionally essential. The performance of larvae on diets containing glucose or fructose was poor, and this was contrary to most of the findings of various authors. On tho other hand, pentoees, usually considered to be poorly utilised by insects, proved almost as good as sucrose in the diet, and an equimolecular mixture of glucose+ fructose was also found to be equally effective. A sucrose concentration of ;oo mgm. per 25 grams of medium was found to be adequate, and this was in reasonable agreement with the sugar requirements of those other phytopha.gous insects for which published results a.re available. The work of a number of authors showed that mustard oil gluco-sides are responsible for evoking the feeding response in Pieris bra.saioae L. larvae, whereas, in the present investigation the inclusion of sinigrin -a mustard oil glucoside -in the diet did not produce any significant i mprovement in the p erforrnance of the larvae. Variations in the sinigrin concentration in the diet also failed to give a positive response. The quantitative nitrogen requirements of the insect were studied using casein as the protein source. The omission of casein from the diet resulted in significantly lower larval weights and proportionately fewer larvae moulting than in the case of larvae reared on diets containing casein. The fifth instar larvae ingested significantly lower eroounts of food when casein was omitted from the diet. The concentration of casein in t he diet finally adopted lay within the range of concentrations used in the diets of other pbytophagous insects studied by other workers. Cystine, one of the amino acids not normally included in the basic list of ten essential amino acids, bas been shown by various authors to be connected with successful moulting in some non-phytophagous insects. In the present studies, the addition of cystine in the diet produced a proportionately higher peroentago of larvae moulting in the earlier instars, and its omission from the diets of the fifth instar larvae caused emergence failures in the adults subsequently produced. This appears to be the first observation of such an effect in a phytophagous insect. The effects of Beta carotene, B vitamins and ascorbic acid were studied. The only detectable effects being retarded larval growth with the addition of~ -carotene, and a higher mortality resulting from the inclusion of ascorbic acid. These results are very curious as all these materials have been added 'With advantage in the diets of various insects, particularly phytophagous ones, rut the possibility of their effects being completely obscured in these short term experiments was discussed. Most of the insects studied have been shown to require cholesterol in their diets. Hence, cholesterol and~ -sitosterol were incorporated in the diets :for Pierie brassigae L. in two different concentrations. The higher concentration of 500 mgm. per 25 grams or medium proved deleterious, while the lowor ono (50 mgm. per 25 grams of medium) produced no detectable improvement, although this concentration was more or less in agreement with tho requirements of those of other phytopbagous inseots studied previously. Similarly, the inclusion of Osbourne and Mendol salt mixture in the diet did not produoe any observed effects. Agar is commonly used in formulating artificial diets and in somo cases it is said to af'fect food consumption. Nutrient agar was tried at di:ff erent concentrations and a level of 2 per cent was found to make the diet cohesive and manageable. In this case no effect on food consumption was observed. Cellophaa was incorporated in the diet to give the medium a loaf like structure but it absorbed too much water, and the modium dried up very quickly. Cellulose powder, however, proved useful in increasing the amount of food consumed on the artificial diet to the level of that on cabbage. The addition of cellulose lowered the coefficient of utilisation considerably, and it was not found possible to correct this without affecting the consumption values. On the other hand, the coefficient of growth was much higher on cellulose diet than on cabbage, the coefficient of metabolism being correspondingly lower. Although the cellulose diet maintained adequate growth of the larvae in these short term experiments, yet the dietary characteristics of cabbage could not be completely reproduced.