The nutritional requirements of locusts—V: Observations on essential fatty acids, chlorophyll, nutritional salt mixtures, and the protein or amino acid components of synthetic diets

Abstract

A requirement for unsaturated fatty acid in Locusta may be fully met by either pure linoleic or linolenic acids but not by arachidonic acid. Augmentation of the standard synthetic diet with crude chlorophyll paste produced no improvement in the growth of either Schistocerca or Locusta. Between 1 and 2 per cent of salt mixture was required in the diet for satisfactory growth of both Schistocerca and Locusta and amounts up to 11 per cent were well tolerated. A salt mixture similar in composition to plant ash was no better than the mammalian nutritional mixture used as a standard, and apparently satisfactory growth was obtained with a much simplified mixture of only four salts. From this it appears that locusts can tolerate large excesses of salts and probably wide variations in the ratios of ions in the diet. Locusta and Schistocerca differ markedly in their ability to grow on diets of different protein composition. A mixture of casein, egg albumen, and peptone was satisfactory for both species, but whereas Schistocerca could complete development at a normal rate of growth on diets containing only casein (of certain grades) Locusta grew poorly and rarely survived the early instar with casein alone, whatever the grade. A similar distinction between the two species was observed on diets containing an amino acid mixture in place of protein. Locusta was unable to survive beyond the second instar, but Schistocerca could develop to the adult stage, although at a reduced rate of growth. It was thus possible to rear Schistocerca, but not Locusta, on a completely defined diet.