Experiments were carried out to determine the active principle(s) in wheat-germ oil responsible for the reproductive effect exerted by this substance on the house cricket, Acheta domesticus L., and also to investigate the physiological effects of the substance(s). The active principle is vitamin E. It exerts an absolute effect on the last nymphal stadium of the male, but the female appears to be unaffected. Spermatogenic activity is disrupted in the absence of the vitamin, resulting in drastic reduction or a total absence of sperm cells in the testes. Withholding the vitamin from insects causes the preoviposition period to be lengthened and fewer eggs to be laid.
The house cricket, Acheta domesticus (L.) (Gryllidae, Orthoptera), is a cosmopolitan and easily available insect, and is most suitable as a test animal for physiological research, as has been pointed out by Stone (1953). However, in spite of the long familiarity of entonlologists with this insect it has received very little attention in the literature, no doubt because it has never been of economic importance in Europe or North America. Such quantitative observations on its development as do exist are rather fragmentary (Kemper, 1937; Stone, 1953; Busvine, 1955). The present article describes, in a somewhat more precise way, the rate of development of the nymph of the house cricket at various temperatures and the number and duration of the nymphal stadia, as well as a satisfactory method of rearing the insect and observations on its fecundity.
Fragmentation of the maternal epicuticle, similar to that occurring normally after 36 hours of incubation at 35 °C, may be induced in ovarian or newly laid eggs or their shells by immersion in buffer solutions at pH 6 to pH 8. Such treatment also increases the activity of the tyrosinase present in the epicuticle. It is suggested that the action of the buffer in causing fragmentation is in part to provide a favorable pH for the reaction(s) involved.
The shell of the newly laid egg of Acheta domesticus (L.) consists of the chorion, in which two layers can be distinguished: an outer exochorion, about 2.5 μ thick; and an inner endochorion, about 0.4 μ thick, which contains lipoid and a tyrosinase. At about the time water absorption begins, the endochorion breaks up, in a more or less regular way, into many small fragments; as a result, spaces are created in the endochorion, and it seems probable that it is this structural change which permits water to be absorbed by the egg. The breaking up of the endochorion appears to be due to phenolic tanning. Also at about the time water absorption begins, the newly formed serosa begins to lay down the serosal cuticle, first an outer lipoid layer, about 0.4 μ thick, which contains a tyrosinase; and then an inner layer, which is laid down continuously while the serosa exists, and which reaches, at the time water absorption ends, a maximum thickness of 8–10 μ. Thereafter the inner layer of the serosal cuticle is steadily resorbed up to the time the egg is hatched, and the vacated shell consists only of the chorion and the lipoid layer of the serosal cuticle. Water absorption appears to be brought to an end by the phenolic tanning of the lipoid layer of the serosal cuticle.
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