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insects). This honeydew accumulates principally on the surface of 

 foliage, and the flies' feeding activities may carry them to all 

 sorts of foliage, not just apple or their native host, hawthorne . 



How do the flies locate foliage, especially foliage with honey- 

 dew on it? Studies conducted in Wisconsin in 1972 by Drs. Guy Bush 

 and Stewart Berlocher (University of Texas), and Dr. Volker Moericke 

 (University of Bonn, West Germany), and myself showed that the flies 

 locate foliage principally, perhaps even exclusively, by its physi- 

 cal characteristics. The size and shape of a foliated tree had 

 some influence on attraction, but the most important factor was 

 foliage color. 



The color of foliage in summer (when flies are active) is green, 

 We found that apple maggot flies (as well as cherry flies in Switzer- 

 land and olive flies in Greece) were more attracted to wooden rectan- 

 gles painted green than to ones painted red, blue, white, gray, or 

 black. What was surprising, however, is that the flies were much 

 more attracted to yellow rectangles than to green ones, especially 

 to the very intensely reflective color of daylight fluorescent yel- 

 low. 



Why should the flies be m.uch more attracted to bright yellow 

 color than to green? With the aid of a spectrophotometer (an in- 

 strument which measures wavelengths of light reflectance), we 

 found that green leaves reflect most light from about 520-580 nano- 

 meters (nm) in the visible spectrum. (Violet reflects most light 

 at 360-430 nm , blue at 430-500 nm , green and yellow at 500-590, 

 orange at 590-630, and red at 630-760 nm) . It turns out that day- 

 light fluorescent yellow paint, just as green leaves, reflects its 

 maximum energy from 520-580 nm. But the amount of energy relected 

 from 520-580 nm by the yellow paint is much greater than by green 

 leaves. We believe that the reason that flies are more attracted 

 to yellow than green is that they perceive yellow as if it were 

 super-bright or super-intense foliage. 



What practical use can be made of this information? We painted 

 daylight fluorescent yellow paint (Saturn Yellow*, manufactured by 

 Day-Glo Corp., Cleveland, Ohio) onto small (about 6" x 8") wooden 

 or cardboard rectangles, coated the rectangles with a clear sticky 

 odorless substance (Bird Tanglefoot*, manufactured by the Tangle- 

 foot Co., Grand Rapids, Michigan) to capture arriving flies, and 

 hung these rectangles in fruit trees in the U.S. and Europe. They 

 proved to be very useful in attracting and capturing apple maggot, 

 cherry maggot, and olive flies and are now being widely used to 

 monitor the activities of these pests in orchards. In fact, when 

 these traps were employed by colleagues in Switzerland (Dr. Ernst 

 Boiler and associates) at the rate of 2.5 per cherry tree in one 

 orchard and 1.7 per tree in another, they captured enough female 

 and male cherry flies to provide a high degree of direct control 



*Trade name 



