Role of host fruit color in the behavior of the walnut fly Rhagoletis juglandis

Observations and sticky-trap tests were used to assess the effect of fruit color on the behavior of adult male and female Rhagoletis juglandis Cresson (Diptera: Tephritidae), a tephritid that infests husks of Arizona walnut i n southeastern Arizona. In the first experiment, during which flies were ob served foraging among walnut models suspended from small walnut trees, mode ls were painted green to appear ripe and uninfested or yellow with brown pa tches to appear ripe and infested. Flies used for this first experiment wer e also of two types: prior to observations, one group of flies had access t o real walnuts for 1.5 days (prior experience) while the other group of fli es was held without real walnut fruits (no prior experience). Regardless of prior experience with real walnut fruits, female flies landed on green mod els more than yellow/brown models. Experienced males also were more likely to land on green models than on yellow/brown models. More interactions also occurred on green models, because there were more landings. In the field behavioral assay, flies from a natural population given a choi ce of green, yellow, and yellow/brown models landed most often on green mod els, and all interactions and oviposition attempts occurred on green models . Flies also distinguished models by color in field sticky trap assays. These results suggest that female response to ripeness cues is innate, whil e males develop a preference for green based on their encounter rate with f emales.