INSECT NUTRITION
Authors: TRAGER WILLIAM 
Published: January 2008

Summary1. Recent work has disclosed the nature of many of the accessory growth factors required by insects. Most of the species which have been studied appear to require only one fat‐soluble factor, cholesterol. Cholesterol can be replaced by certain other related sterols, depending on the species of insect, but it cannot be replaced by sterols of the vitamin D group. A fundamental difference evidently exists between insects and vertebrates with respect to their requirements for fat‐soluble growth factors. On the other hand, the water‐soluble growth factors for insects which have thus far been determined are all identical with the water‐soluble vitamins of the B group required by vertebrates. It seems probable that all insects require these substances, and the necessity of one or more for normal growth has already been demonstrated for species of the orders Hemiptera, Coleoptera, Lepidoptera, and Diptera. Some species of insects which contain intracellular symbionts have been found to develop normally on diets deficient in some of the B vitamins. If such insects are artificially freed of their symbionts they then require in their diet all the water‐soluble factors which are required by related species which naturally are free of symbionts.2. Various salts are essential constituents of the diet for most insects. For several species, calcium has been found to have especially striking effects, but Drosophila melanogaster appears to be able to develop without calcium. Insects differ somewhat in their carbohydrate requirements. Some species, like the mealworm Tenebrio molitor, can develop only on a diet containing a preponderance of carbohydrate over protein. Little is known concerning the amino‐acid requirements of insects, but they are certainly at least as extensive as those of the vertebrates.3. Because of the difficulties attending nutritional work with the large groups of leaf‐feeding and parasitic insects, it has not yet been possible to obtain information concerning the chemical nature of their specific nutrients. Such information may turn out to be of special interest and importance, especially in its relation to the peculiar host‐parasite specificities which exist in these groups of insects. Distinct effects have been reported of different natural foods on the development and reproductive capabilities of such insects, as well as of others more amenable to experimental manipulation. The fecundity of an insect may be affected by its food as a larva as well as by its food in the adult stage. In one case it has been found that the food of the parent insect as an adult profoundly affected the development of its offspring, so much so that offspring fed on a superior diet, but descended from parents fed on an inferior diet, grew less well than offspring fed on an inferior diet but descended from parents fed on a superior diet.4. Food selection appears to be determined in most cases by characters of the food which have no direct connexion with fundamental nutritional requirements.5. The polymorphism of aphids, paedogenetic flies, and certain other insects, and the queen and worker castes of the honey‐bee, are greatly influenced, if not primarily determined, by nutritional factors. Such factors may also be of importance in caste determination among the ants and termites. In no case has the nature of these forms determining dietary factors been discovered.