Auxotroph for purine nucleoside. In viable allelic combinations, reduced wings with extra wing vein material, bristles and hairs along the wing margin are missing or deranged, macrochaetes on the body are thin and short. Eye colour: reddish-brown. Hemizygotes die as pupae. Hemizygous adult escapers are seen at low temperatures, they have malformed and undifferentiated tarsal segments and die within a few days.