A comparison of phototactic responses to red and green light in Glossina morsitans morsitans and Musca domestica

. Experiments were performed on male Glossina morsitans morsitans Westw. and female Musca domestica L. to investigate their phototactic responses at long wavelengths. In both species, green light was less attractive than red (relative to a 400 nm standard). In M. domestica this can be adequately explained by an intensity‐dependent phototactic reversal at wavelengths above 500 nm; red light could be matched in attractiveness by a low intensity green light, implying that no true red‐green discriminating ability exists, but that red is perceived as a dim green. Although a partial phototactic reversal was also observed in G. m. morsitans at 525–575 nm, no tested intensity of green matched red in attractiveness. It appears therefore that G. m. morsitans may be an unusual dipteran in possessing a method of discriminating red and green light independently of intensity. Both species also resolved near‐UV from green.