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Factors that interfere with attraction of apple maggot flies to traps were studied to provide a baseline for optimal trap deployment in apple orchards. I found a four-fold increase in captures of mature flies when butyl hexanoate was added to unbaited red spheres. The addition of ammonium carbonate or food presence did not affect mature fly response to traps. Wild flies immigrating into commercial orchards were primarily mature and not hungry for protein. Flies released outside blocks of apple trees of different sizes were intercepted in larger proportions by traps on small and medium sized trees than on similar traps on large trees. Overall trap performance was not strongly affected by orchard structure. Released flies were recovered in larger proportions by traps on McIntosh trees than by traps on Red Delicious trees bearing larger darker fruit. Visual competition became stronger as Red Delicious apples grew in size and turned in color. Decreased trap apparency on Red Delicious trees was compensated for by increased residence time of wild flies. Wild flies were captured in larger numbers by red spheres and Ladd traps than by yellow panels. Red spheres lost capturing power towards harvest when competing visually with red fruit. Ladd traps were not equally affected, but were more sensitive to trap positioning than red spheres. Red sphere effectiveness was restored after harvest. Optimal trap positioning may need to be revised. Wild fly accumulation on traps on tees of different apple cultivars during the growing season revealed that fly distribution in orchards is not exclusively governed by fruit ripening but rather by apple maggot preferences for some cultivars. Although ripening stage affected the onset of increases in fly accumulation on traps, some cultivars never accumulated many flies during the growing season. Apple maggot preferred to oviposit in sweet moderately firm fruit, but avoided ovipositing in excessively hard or soft fruit of different apple cultivars. Females also avoided fruit of late cultivars, even when sugar content and firmness were high and moderately high. Ovipositional cultivar preferences did not necessarily translate into greater fly accumulation on traps in our orchard study.