than extracts of fruit of four nonhost plants two 

 weeks after bloom (RI = 0-8) (Table 1). Extracts of 

 Mcintosh blossoms or fruit at one, two, three or four 

 weeks after bloom were about equally attractive to 

 PCs (RI = 33-50) and were more attractive than ex- 

 tracts made five weeks after bloom (RI = 0) (Table 

 2). Extracts of wild plum fruit made one or two 

 weeks after bloom (RI = 58) were more attractive 

 than extracts of wild plum blossoms or extracts of 

 fruit made three or four weeks after bloom (RI = 

 25-29) or five weeks after bloom (RI = 4) (Table 2). 

 Extracts of Mcintosh fruit, 

 leaves and twigs were about 

 equal in attractiveness to 

 PCs when made one week 

 after bloom (RI = 39-44) 

 (Table 3). When made four 

 weeks after bloom, extracts 

 of Mcintosh fruit and leaves 

 were about equally attrac- 

 tive (RI = 42-48), whereas 

 extracts of twigs were rather 

 unattractive (RI = 17) (Table 

 3). Extracts of whole bodies 

 of PC females (RI = 45) and 

 males (RI = 31) were simi- 

 larly attractive to PC fe- 

 males (Table 4). 



Conclusions 



We postulated at the 

 outset that PCs could ex- 

 hibit greater attraction 

 toward extracts of host 

 fruit than extracts of 

 nonhosts fruit. Our re- 

 sults supported this hy- 

 pothesis and suggest that 

 host plants emit particu- 

 lar attractive compounds 

 or blends of compounds 

 that are not characteris- 

 tic of nonhost plants. 

 Peak attractiveness of 

 wild plum fruit (the na- 

 tive host of PC) occurred 

 one to two weeks after 

 bloom. Peak attractive- 

 ness of Mcintosh fruit ex- 

 tended to four weeks af- 

 ter bloom. Neither wild 

 plum nor Mcintosh fruit 

 were attractive five 

 weeks after bloom. Interestingly, compounds 

 present in Mcintosh trees attractive to PCs appear 

 to be emitted rather equally by fruit, twigs, and 

 leaves one week after bloom and by fruit and leaves 

 four weeks after bloom. Finally, the finding that 

 extracts of whole bodies of each sex of PC were at- 

 tractive to PC females suggest the existence of at- 

 tractive pheromone. 



Together, the findings presented here strongly 

 suggest that synthetic equivalents of odors of host 

 plants (particularly of fruit, twigs and leaves one 



Fruit Notes, Winter, 1996 



