Isolated with regard to poor response to light in fast phototaxis tests; both sexes are sluggish in this regard. Males in this strain do not mate with females in darkness; in the light, males court and mate with females (40-50%, within 10 m) and other males with equal vigor; the latter behavior includes formations of chains and rings of intermale courters, as well as pseudo-copulation attempts; courtees in these circumstances do not exhibit wing-flick repelling responses characteristic of wild-type males. Spectral sensitivity studies of the light-elicited courtship activities showed 420-515 nm to be effective (thus orange/red range ineffective); yellow light was perhaps the most stimulatory; quick turn-ons and turn-offs of intermale courtships could be effected by intermittent exposures to yellow and red light, respectively.