none Rhagoletis boycei; Rhagoletis juglandis; HYMENOPTERAN-HOSTS; Biosteres juglandis; Host location by parasite; PLANT-HOSTS; Juglans major (walnut); Parasite location by hymenopteran parasite; ARIZONA-; South east, Huachuca Mountains, Garden Canyon; Location by hymenopteran parasite Biosteres juglandis; DIPTERAN-HOSTS; Rhagoletis boycei & Rhagoletis juglandis; Host location by parasite; ARIZONA-; South east, Huachuca Mountains, Garden Canyon; Dipteran host location Behavior of the parasitic wasp Biosteres juglandis, which attacks tephritid fly larvae feeding in the husks of walnut fruits, was studied in the field and in a greenhouse cage. Assays were conducted to determine 1) whether parasitic wasps could locate host-infested fruits preferentially over uninfested fruits; and 2) whether wasps could assess the number of hosts available in a fruit before or after landing. Results indicate that wasps discriminate between infested and uninfested fruit before landing, and assess the number of hosts after landing.