DISTANCE OF RESPONSE TO HOST TREE MODELS BY FEMALE APPLE MAGGOT FLIES, RHAGOLETIS-POMONELLA (WALSH) (DIPTERA, TEPHRITIDAE) - INTERACTION OFVISUAL AND OLFACTORY STIMULI

Mature female apple maggot flies, Rhagoletis pomonella (Walsh), were r eleased individually onto a single potted, fruitless hawthorne tree in the center of an open field. The tree was surrounded by four 1-m(2) p lywood host tree models painted green or white, with or without synthe tic host fruit odor (butyl hexanoate), and placed at one of several di stances from the release tree. Each fly was permitted to forage freely on the release tree for up to 1 hr, or until it left the tree. Flies left the tree significantly sooner when green models with host fruit w ere present at 0.5, 1.5, or 2.5 m distance from the release tree than when these models were placed at a greater distance (4.5 m) from the r elease tree or when no models were present. Flies responded detectably to 1-m(2) models without odor up to a maximum distance of 1.5 m. Thes e results suggest that female apple maggot flies did not detect green 1-m(2) models with odor 4.5 m away or models without odor 2.5 m or mor e away. Flies responded to white models with and without odor to a muc h lesser extent, both in terms of response distance and flight to and alightment upon models. Increasing model size to 2 m(2) increased the distance to 2.5 m at which flies responded to green models without odo r. Decreasing model size to 0.5 m(2) reduced fly responsiveness to gre en or white models. The presence of host fruit odor alone, without the visual stimulus of a green model, did not influence residence time on the release tree.