Homozygous larvae are sensitive to X rays, UV light, formaldehyde, nitrogen mustard and methyl methanesulfonate. Homozygous females have reduced reproductive capacity, which can be partially rescued when homozygous oocytes are fertilised by wild-type sperm. There is a small but significant increase in X and 4th chromosome non-disjunction.

Larval survival hypersensitive to exposure to methyl methanesulfonate, nitrogen mustard, formaldehyde, ultraviolet light and X rays. Fecundity of homozygous females reduced, although partial rescue effected by fertilization with sperm carrying mus203⁺. Small but significant increase in X- and fourth-chromosome nondisjunction in the first but not the second meiotic division; X-chromosome recombination reduced to 80% normal levels.