Abstract
It was found that the larval development of the cabbage armyworm, Barathra brassicae L., is accelerated when it is reared under crowded conditions (Hirata, 1956).
In this paper, the writer has analyzed some regulating mechanisms of the larval development comparing two population densities of 1 and 5 individuals per vessel which were kept in darkness under the controlled condition of temperature at 25°C. The results obtained are summarized as follows.
1. The larvae of crowded population complete their larval stage in 90 per cent of the length of time of that of the isolated population.
2. The accerelation rate of larval development in crowded population was higher in the feeding stages than in the moulting stages.
3. The frequency curves of the time of the beginning and end of the moulting stage were unimodal ones in young larval stages, but, with the growth of larvae, they became multimodal ones. This modality in the frequency curve was mainly the result of the daily rhythm of the beginning and end of the moulting. In the crowded population, the increasing trend of modality was not so conspicuous as the isolated population because it has a shorter duration of beginning and end of moulting as compared with the isolated population.
