Attraction of Plum Curculio Adults to 

 Host-plant and Pheromonal Extracts 



Tracy Leskey^ Catherine Bramlage^ Larry Phelan^, 

 and Ronald Prokopy^ 



^Department of Entomology, University of Massachusetts 

 ^Ohio Agricultural Research and Development Center 



Plum curculios (PCs) use odor to locate indi- 

 vidual host fruit at close range (Butkewich and 

 Prokopy 1993, J. Chem. Ecol. 19:825-835). PCs, 

 like other weevils, also may be attracted to phero- 

 mones produced by the same or opposite sex. In 

 1995, we began to test PC attraction to various plant 

 odor and pheromonal extracts using a simple bioas- 

 say. In 1995, we conducted bioassays of PC re- 

 sponses to extracts of (1) host and nonhost plants, 

 (2) wild plum and Mcintosh fruit at different stages 

 of development, (3) parts of Mcintosh trees, and (4) 

 whole bodies of PC females and males. 



Materials and Methods 



Hexane extracts were made from fruit collected 

 two weeks after bloom from the following plant 

 types: Mcintosh trees, mountain ash trees, barberry 

 bushes, dogwood bushes, and honeysuckle bushes. 

 We also made extracts of blossoms or fruit collected 

 from wild plum and Mcintosh trees at the follow- 

 ing stages of development: bloom and one, two, 

 three, four, and five weeks after 

 bloom. Further, we made extracts 

 of Mcintosh fruit, twigs, and leaves 

 collected one and four weeks after 

 bloom. Hexane, pheromonal ex- 

 tracts were made from whole bodies 

 of female or male PCs starved for 24 

 hours. 



PCs used in bioassays were col- 

 lected from unsprayed wild plum 

 and apple trees. For all plant odor 

 tests, PCs of mixed sexes were 

 starved 24 hours prior to testing. 

 Tests were conducted at the begin- 

 ning of darkness. One PC was 

 placed into each test Petri dish and 

 allowed to move toward volatiles 

 emitted from either a plant odor ex- 

 tract in hexane or hexane alone (as 



a control). For all pheromonal extract tests, one 

 PC known to be female and starved 24 hours prior 

 to testing was placed into each test Petri dish and 

 allowed to move toward either a pheromonal extract 

 in hexane (amount equivalent to that extracted from 

 one female) or hexane alone (as a control). PCs were 

 allowed 2 hours to respond. 



To measure the power of a treatment (i.e., the 

 power of a potentially stimulating odor) we used a 

 Response Index (RI). The RI was calculated by sub- 

 tracting the number of PCs responding to the con- 

 trol from the number responding to the treatment, 

 dividing this amount by the total number of PCs 

 tested, and multiplying by one hundred. The 

 greater the RI value, the more attractive was the 

 stimulus. We considered a RI value of 25 as the 

 minimum for suggesting attractiveness. 



Results 



Extracts of Mcintosh fruit two weeks after 

 bloom (RI = 38) proved much more attractive to PCs 



Fruit Notes, Winter, 1996 



