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Egglaying by apple maggot females is accomplished when the fe- 

 male arrives on a susceptible fruit, raises up on its legs, bores 

 with its ovipositor through the skin of the fruit into the flesh, 

 and deposits a single egg. The ovipositor is a needle-like protru- 

 sion from the posterior of the abdomen through which the egg is 

 passed into the fruit. Following egg deposition, the female with- 

 draws its ovipositor from the fruit, and then proceeds to circle 

 around the fruit for about 30 seconds, dragging its fully-extended 

 ovipositor on the fruit surface behind itself. After this, the fe- 

 male cleans its ovipositor for a few seconds and then flies off the 

 fruit. 



About 5 years ago, I became very curious as to why the females 

 engaged in this rather elaborate behavior of ovipositor-dragging. 

 Actually, my observations of maggot fly oviposition in nature re- 

 vealed that only about half the cases in which females were seen 

 attempting to bore into a fruit culminated in ovipositor dragging 

 while the other half did not. When I examined the fruit, I found 

 that among females which did drag their ovipositors after attempt- 

 ing boring, 901 had in fact deposited an egg. On the other hand, 

 among females which did not drag their ovipositor after attempted 

 boring, only 2% had deposited an egg. Thus, there was a clear pos- 

 itive relation between egglaying and dragging the ovipositor after- 

 ward. This suggested that the act of ovipositor dragging might be 

 a mechanism for marking the fruit with some sort of substance to 

 signify the presence of an egg. 



I investigated this possibility in a Wisconsin sour cherry 

 orchard heavily infested by apple maggot flies, which attack sour 

 cherries in that state. I held a sour cherry by a thin wire at- 

 tached to the stem, brought the cherry to within a few inches of a 

 female on a cherry tree, and waited for the female to fly onto the 

 cherry. Two types of cherries were offered: (1) a clean cherry 

 never visited or infested by an apple maggot, and (2) a cherry in 

 which another apple maggot female had just laid an egg and dragged 

 her ovipositor. It turned out that 621 of the females that landed 

 on the first type of cherry attempted egglaying, while 01 arriving 

 on the second type attempted egglaying. Clearly, there was some 

 sort of deterrent to repeated egglaying associated with the second 

 type of cherry. 



The question now arose as to whether this egglaying deterrent 

 originated from the eggs, the flies, or the fruit. To answer this 

 question, I offered the females 4 types of cherries: (1) a cherry 

 in which a female had laid an egg but was not allowed to drag her 

 ovipositor afterward, (2) a cherry with a pin prick, and the exuding 

 fruit juice spread over the fruit surface afterward, (3) a cherry 

 never visited by any flies, and (4) a cherry in which no egg was 

 laid, but on which a female (transferred there from another cherry) 

 had dragged her ovipositor. The results showed that 60-651 of fe- 

 males that arrived on each of the first 3 types of cherries attemp- 

 ted egglaying compared with 0% that arrived on the fourth type. 



