pies (the same color, size, and shape as real apples) near real ap- 

 ples on a tree and observing that just as many males and females 

 landed on the wooden models as on the real apples. 



What then are the particular visual characteristics of indi- 

 vidual apples which the flies cue in on? I found that the spheri- 

 cal-type shape of an apple is a very powerful visual stimulus, and 

 that wooden spheres attract many times more flies than wooden cubes, 

 cylinders, or rectangles of the same color and size. Color is al- 

 so important, the most preferred colors of wooden, apple-size spheres 

 being red and black, the least preferred being light green, light 

 orange, and yellow. My interpretation of this is that dark-colored 

 fruits stand out in greater contrast (and are thus more readily 

 detectable) against the background of tree foliage and skylight 

 than are light-colored fruits. Just as humans would, so also would 

 the flies eventually discover all the yellow or yellow-green apples 

 on a tree. But the flies, as well as humans, have an easier time 

 locating dark-colored apples. Size of apple is another important 

 stimulus to the flies. The)' are not as attracted to small apples, 

 one inch or so in diameter, as they are to 3-inch-diameter apples. 

 Early in the season, they are just as attracted to red spheres 12 

 inches in diameter (only in Texas do apples grow so big!) as to 

 ones 3 inches in diameter. But as the season progresses, the flies 

 apparently learn, through practice and experience, the normal size 

 of apples, so that by mid-season, they show a decided preference 

 for 3-inch red spheres over 12-inch ones. 



After an apple maggot m.ale arrives on an apple, it waits there, 

 visually searching the vicinity for the presence of a female. Re- 

 cently, I found that virgin females are attracted from a short dis- 

 tance to a sex odor given off by the males. Also, we found that 

 when a female visits an apple, it lays down an odor of short dura- 

 tion (2-3 hours) that acts to arrest a male arriving on that apple. 

 This odor lets the male know that a female has recently been there, 

 and that it would pay the male to wait there and watch for the fe- 

 male. 



What practical use can be made of this information to aid in 

 our apple maggot control programs? It turns out that a very power- 

 ful visual trap for attracting and capturing the flies can be made 

 simply by painting a bocce or croquet ball (3-4 inches in diameter) 

 dark red, coating it with Bird Tanglefoot* (manufactured by the 

 Tanglefoot Company, Grand Rapids, Michigan) and hanging it by wire 

 in an apple tree of a maggot-favored variety - Astrachan, Wealthy, 

 Puritan, Early Mcintosh, Cortland, Delicious, Spy. This ball or 

 sphere effectively mimics the visual stimulus of an apple, and is 

 highly attractive to male apple maggot flies in a mating mood and 

 to females in a mating and egglaying mood. It is extremely impor- 

 tant, however, that the flies be able to clearly see the sphere. 



*Trade name 



