Reduces incidence of melanotic masses in tu(2)bw homozygote from 85-100% in su(tu-bw)1/+ to 5-10% in su(tu-bw)1 homozygote. Suboptimal ratios of pentose nucleotides, cholesterol deficiency, or excess L-tryptophan in the larval diet, as well as X irradiation of embryos, increase incidence of melanotic masses in tu(2)bw; su(tu-bw)1 homozygote. Glass and colleagues attribute this to an effect on su(tu-bw)1, whereas Burnet and Sang believe the reaction controlled by tu(2)bw is affected. Does not suppress tu(2)bw. RK3.