Biotin as a Possible Growth Factor for Insects

Abstract

IT has been shown for several insects, namely, Lucilia1, Drosophila2 and Tribolium3, that the larva requires a growth factor which is contained in the water-insoluble fraction of yeast and is not fat-soluble. This can be easily demonstrated with Tribolium confusum. This beetle, which normally breeds on wholemeal flour, grows almost equally well on a diet consisting of casein, glucose, yeast, cholesterol, salts and water added to make a water content of about 15 per cent. If a water-soluble yeast extract (prepared according to Chick and Roscoe4) is supplied instead of yeast, growth is very much retarded (1) (see accompanying table), but normal growth is restored by adding the water-insoluble fraction of yeast (2). The same result has been obtained with the following three species of beetles which are all common pests on stored food: Sitodrepa panicea, Lasioderma serricorne and Silvanus surinamensis. The need for an 'insoluble' factor in yeast seems, therefore, to be of general occurrence in insects. This factor is not fat-soluble, because the adding of a chloroform-soluble extract of yeast (3) or of wheat germ oil (4) only very slightly improves diet (1). It is not considered to be entirely absent from yeast extract because in that case development would presumably be impossible. This view is supported by the fact that tripling the amount of yeast extract improves tine diet considerably (5). A water-soluble liver extract shows about the same deficiency (6) as the corresponding yeast extract (1). The filtrate of autoclaved yeast improves diet (1) and so does marmite (7) (which is virtually an autolysed yeast extract).