The courtship index of heterozygous males towards decapitated Canton-S males is significantly higher than that of wild-type males towards decapitated Canton-S males. The courtship index of heterozygous males towards decapitated Canton-S males is significantly lower than that of heterozygous prosV1 males towards decapitated Canton-S males. Homozygous flies appear selectively disadvantaged in the presence of prosV65/TM3 heterozygotes; after more than 50 generations in a stock in which prosV65 is maintained over TM3, the frequency of homozygous flies stabilised at around 30-35%.