1. The larvae of the moths belonging to the genus Ephestia, E. kuehniella, E. elutella and E. cautella grow well on artificial diets which also contain wheat-germ oil. In the absence of wheat-germ oil growth is slow, the mortality high and the moths fail to emerge from the pupae.

2. With suboptimal quantities of wheat-germ oil moths emerge with the wings lacking in scales.

3. The saponifiable fraction of wheat-germ oil is necessary for emergence and good scales, and the unsaponifiable fraction for good growth.

4. The active substance in the saponifiable fraction is linoleic acid. Linolenic acid has approximately the same effect as linoleic acid. Oleic acid has no effect.

5. The active substance in the unsaponifiable fraction is vitamin E (α-tocopherol) and possibly other antioxidants. One of the functions of vitamin E is that of an antioxidant which stabilizes linoleic acid. In this respect vitamin E can be replaced by ethyl and propyl gallates, or by ascorbic acid.

6. Apart from this stabilizing effect on linoleic acid, the unsaponifiable fraction of wheat-germ oil, or vitamin E, have also an independent growth effect. There are also indications that linoleic acid has a growth effect.

7. It is shown that the effect of a number of vegetable and animal fats on scales and emergence is strictly parallel to their linoleic acid content.

8. With cod-liver oil, halibut-liver oil, lard and butter growth is fast, while the effect on scales and emergence is small or nil. The growth effect of codliver oil is mainly or partly due to its content of docosahexenoic and probably other highly unsaturated fatty acids.

9. Large quantities of cereal starches in the diet have a favourable effect on scales and emergence which is attributed to the presence, in starch, of impurities of linoleic acid. No such effect has been encountered with potato starch which is free of linoleic acid.

10. The similarities and dissimilarities in the linoleic acid deficiency of the rat and Ephestia have been discussed.

11. The symptoms of the linoleic acid deficiency of Ephestia are similar, if not perhaps identical, with those of a genetical condition known as Glasflügeligkeit

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