Abstract
1. Competition experimets between the brown gene and its wild type allele were carried out by using population bells and ordinary culture ottles. The mutant brown gene was almost always superior to it wild type allele.
2. The parental population size of 50 to 150 per generation was sufficient to suppress random gene-fixation and to secure an increase of frequency of the brown genes. Therefore, the adaptive superiority of the brown gene to its wild type allele under experimental conditions was regarded to be considerably high.
3. The following properties of brown homozygote were found and considered as factors of the adaptive superiority of the brown gene in competition experiments.
a) The viability of brown. homozygote increased under high larval population density.
b) The larvae of brown homozygotes grew more rapidly in mixed culture with wild-type larvae than in pure culture.
