Two Odor Compounds Hold Promise 

 for Increasing Trap Effectiveness for 

 Plum Curculio 



Tracy Leskey, Max Prokopy, Anthea Yanopolous, Margaret Young, Brian Hogg, 



Fidelma Boyd, and Ronald Prokopy 



Department of Entomology, University of Massachusetts 



Larry Phelan 



Department of Entomology, Ohio State University 



There has been no trap developed for plum 

 curculios (PCs) that successfully detects the beginning 

 of PC activity in orchards each spring. Traps for other 

 species of weevils such as the cotton boll weevil and 

 the sugar cane weevil use a combination of attractive 

 compounds present in host plant odors and weevil-pro- 

 duced pheromones to increase trap effectiveness. PCs 

 are attracted to odors produced by their host fruit over 

 short distances as reported in the 1 996, 1 997, and 1 998 

 Winter Issues of Fruit Notes. Under field conditions, 

 PCs are attracted to host fruit odors at distances up to 

 3 yards. Eller and Bartelt of Illinois found that male 

 PCs produce an aggregation pheromone called 

 grandisoic acid. Therefore, we decided to screen 18 

 of the 19 compounds present in plum odor that were 

 identified by Larry Phelan's lab at Ohio State Univer- 

 sity in hopes of finding attractive compounds that could 

 be used in combination with grandisoic acid to improve 

 trap performance. Compounds were tested in the labo- 

 ratory and in the field to identify those that were most 

 attractive to PCs. 



Materials & Methods 



A profile of volatile compounds that comprises the 

 odor of freshly picked plum fruit (2 weeks after bloom) 

 was completed in the laboratory of Larry Phelan using 

 a gas chromatograph and mass spectrometer. The 

 compounds listed in Table 1 plus phenol were identified 

 as comprising plum odor. All compounds were evalu- 

 ated as potential attractants for PCs in laboratory and 

 field experiments with the exception of phenol, which 



is highly toxic to mammals. Compounds were tested in 

 the laboratory at three concentrations (1, 0.1, and 

 0.01%) and in the field at two concentrations (5 and 

 0.5%). 



PCs used in laboratory bioassays were collected 

 from unsprayed wild plum and apple trees. For all labo- 

 ratory tests, PCs were starved 24 hours prior to test- 

 ing. Tests were conducted at the beginning of dark- 

 ness. A 75 ul aliquot of the compound (the treatment) 

 was pipetted onto a small cotton wick placed next to 

 one of the two pipette tips that served as ports into a 

 Petri dish test chamber. Either 75 ul of hexane or wa- 

 ter (depending on the solubility of the compound) was 

 used as a solvent control and was pipetted onto a sec- 

 ond cotton square placed next to the other pipette port. 

 Handling of PCs was kept to a minimum. A single PC 

 was placed gently in the center of each Petri dish test 

 chamber. Each time a specific compound was tested, 

 12 PCs were tested singly in individual dishes and kept 

 together on a tray. Dishes were then moved immedi- 

 ately to the testing room. All bioassays lasted 2 hours, 

 and all compounds were tested at least four times at 

 each concentration ( 1 2 individual PC per tray x 4 trays 

 = 48 individual PCs tested per compound and concen- 

 tration). To measure the level of attraction to a par- 

 ticular compound (the treatment), we used a Response 

 Index (RI). The RI was calculated by subtracting the 

 number of PCs responding to the control (C) from the 

 number responding to the treatment (T), dividing this 

 amount by the total number of PCs tested each time, 

 and multiplying by one hundred. Thus RI = [(T - C) / 

 12] x 100. The greater the RI value, the more attrac- 



Fruit Notes, Volume 63 (Number 3), Summer, 1998 



15 



