Visual responses of apple maggot flies, Rhagoletis pomonella (Diptera: Tephritidae): Orchard studies

Abstract

Apple maggot flies, Rhagoletis pomonella, were found to be highly responsive to visual stimuli, with maximum responses dependent upon color, shape, and size characteristics of the stimulus. Each sex had a significant preference for yellow 30×40 cm rectangles over green, orange, red, blue, violet, black, white and clear rectangles of the same size. On the other hand, each sex had a significant preference for red, blue, violet, dark organge, and black spheres 7.5 cm in diameter over green, light orange, yellow, white, and clear spheres of the same size. Both sexes had a significant preference for 7.5 cm spheres over equivalent-sized cubes, cylinders and rectangles. As the diameter of a sphere was increased from 7.5 to 45 cm, there was an orderly and significant decrease in the attractiveness of those that were darkcolored (red) but a progressive and significant increase in the attractiveness of those that were yellow. The flies did not congregate on trees with apples or respond strongly to 7.5 cm, darkcolored spheres until they were sexually mature (at least in the case of females). Relative to other colors, females were often significantly more attracted than males to yellow. The attractiveness of an olfactory stimulus eliciting feeding-type reactions was enhanced to a substantial degree when employed in conjunction with a 30×40 cm yellow rectangle, but to only a very slight degree when in conjunction with a 7.5 cm red sphere. Evidence presented suggests the following explanation for these findings. The flies are attracted to large surfaces of yellow because they react to yellow, on the basis of true color discrimination, as if it were foliage on which to find food. On the other hand, they are attracted to small, dark-colored spheres because they react to such spheres as they react to apples, which are the oviposition site and which also appear to serve as a rendezvous site for the sexes in mating activity. Once the flies have arrived on apple trees, they detect apples solely through vision. Red, blue, violet, dark orange, and black small spheres are preferred over small spheres of other colors on the basis that they stand out in strongest contrast against the background and not on the basis of true color discrimination. Large, dark-colored spheres are unattractive because the range of sphere sizes eliciting positive responses is near the size of an apple. These findings have proven useful in designing effective devices for sampling orchard populations of the flies and may also prove useful in fly control. © 1968 North-Holland Publishing Co.