Several Host-odor Compounds are 

 Attractive to Plum Curculio Adults 



Ronald Prokopy, Starker Wright, Anthony Minalga, Bradley Chandler, 



Jonathan Black, and Tracy Leskey 



Department of Entomology, University of Massachusetts 



Larry Phelan and Richard Barger 



Department of Entomology, Ohio State University 



As revealed in the preceding two articles, traps devel- 

 oped for monitoring plum curculio (PC) adults in com- 

 mercial orchards are unlikely to succeed unless baited 

 with powerful attractive odor, the most promising type 

 being attractive host fruit odor. To date, 56 compounds 

 have been identified as components of odor of plum or 

 apple fruit at the most attractive stage to PC (2 weeks 

 after bloom). In the Summer \99%\s,s,\ieoi Fruit Notes, 

 we presented results of 1 998 tests evaluating 1 6 of these 

 56 compounds. Two were found to be attractive to 

 PC: limonene and ethyl isovalerate. Here, we describe 

 results of 1999 tests in which 30 of the 56 host-odor 

 compounds (including the 16 compounds of 1998) were 

 evaluated in field tests for attractiveness to PC. 



Materials & Methods 



Of the 56 compounds, 46 were identified in the 

 laboratory by Larry Phelan in Ohio and 10 were iden- 

 tified in the laboratory of Sylvia Dom in Switzerland. 

 We chose to evaluate the 30 compounds that were most 

 readily available from a commercial source (Aldrich 

 Chemical Company) and least expensive to purchase 

 (less than $5.00 per gram). 



Each compound was introduced into a 2-dram poly- 

 ethylene vial and assessed at three different rates of 

 odor release, so as to create a low, moderate, or high 

 dose of odor concentration in the surrounding air. 

 Release rates were varied either by adding mineral oil 

 to the contents of a vial to reduce release rate or drill- 

 ing small holes in a vial just beneath the cap to in- 

 crease release rate. Intended release rates for each 

 compound were 3, 12, and 48 milligrams of odor per 

 day, but it was not always possible to achieve intended 



precision with each compound. 



Compounds were assayed in association with yel- 

 low-green boll weevil traps placed on the ground be- 

 neath perimeters of unsprayed apple tree canopies in 

 Massachusetts and Ohio. PCs frequently drop from 

 host tree canopies to the ground and thus may encoun- 

 ter odor from a nearby baited trap. Each trap was baited 

 either with two vials containing the same compound 

 at the same release rate or two empty vials. Vials were 

 suspended vertically by wire attached to the base of 

 the screen funnel top of the trap. Over a 7-week pe- 

 riod from early May to late June, 360 traps were de- 

 ployed in Ohio and another 360 in Massachusetts for 

 compound evaluation. Traps were examined for cap- 

 tured PCs and rotated in position daily or every other 

 day. 



To measure attractiveness of a particular release 

 rate of a particular compound, a Response Index (RI) 

 was created by subtracting the number of PCs respond- 

 ing to an unbaited control trap (C) from the number 

 responding to a baited trap (BT), dividing by the total 

 number of PCs captured by the C and BT traps and 

 multiplying by 100. Thus RI = [(BT-C)/(BT+C)] x 

 100. The greater the RI, the more attractive the com- 

 pound at that release rate. 



Results 



Results (Table 1 ) show that 1 3 of the 30 compounds 

 had RI values of 32 or greater (= minimum RI value 

 for statistical significance) at the most attractive re- 

 lease rate. In descending order of attractiveness, these 

 were E-2- hexenal (RI=90), hexyl acetate (67), decanal 

 (64), limonene (64), geranyl propionate (59), 1- 



Fruit Notes, Volume 64 (Number 3), Summer, 1999 



