Similar to that of other Rhagoletis species, color response of the walnut husk fly, R. completa Cresson, varies with the shape of an object. Yellow was the preferred color when combined with a rectangular trap shape. Green rectangles were also quite attractive. When given a choice of yellow, green, red, and blue spheres, husk flies preferred green spheres, especially those whose reflectance pattern matched that of the walnut husk. Yellow spheres were as attractive as green spheres but only during the first weeks of fly emergence when reproductive activity was still low. The response of R. completa to green spheres can be explained in relation to its reproductive behavior. Green spheres apparently mimic the nuts, which are the mating as well as the oviposition site for the husk fly. No difference was detected in color response between male and female husk flies. Ammonia odor, generally considered a feeding-type olfactory stimulus, enhanced the response to yellow rectangles and green spheres several fold but at a loss of selectivity. This research supports the use of yellow rectangles and green spheres for monitoring.
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Riedl et al. (1985) studied this question.