Evaluation of Odor Combinations 

 for Attracting Plum Curculios to 

 Trap Trees 



Ronald Prokopy, Bradley Chandler, Sara Dynok, Elisa Gray, Matthew Harp, 



Anne Talley, and Jaime Pinero 



Department of Entomology, University of Massachusetts 



In the preceding article, we presented data showing 

 that apple trees whose branches were baited with a 

 combination of benzaldehyde (BEN) plus grandisoic 

 acid (GA) functioned as "trap trees" for plum curculios 

 (PCs). Adult PCs aggregated preferentially on such trap 

 trees, thereby paving the way for growers and 

 consultants to sample only trap trees (rather than 

 additional other trees) for signs of fresh PC injury to 

 fruit. 



Here, we report results of a 2002 study in 

 commercial apple orchards in which we evaluated 

 several different odor combinations in association with 

 trap trees to determine if there might be a more 

 attractive combination than BEN plus GA. The 

 rationale underlying this study lay in the proposition 

 that the more attractive the odor bait, the more attractive 

 the trap tree and hence the fewer number of trap trees 

 needed to acquire an accurate assessment of the 

 seasonal course of PC injury to fruit. 



Materials & Methods 



We established nine treatment types in each of 1 1 

 commercial apple orchards. These included BEN plus 

 GA plus one of five other host-derived odor sources 

 known from previous studies (Fruit Notes 2000) to be 

 at least somewhat attractive to PCs: ethyl isovalerate, 

 limonene, hexyl acetate, Z-3 hexenyl acetate and E-2- 

 hexenal. Also included as treatments were BEN plus 

 GA, GA alone, BEN alone, and no odor (control). As 

 described in the preceding article, BEN was released 

 fi^om polyethylene vials at a rate of 40 mg per day per 

 tree and GA at a rate of 1 mg per day per tree. The 

 other five odor sources likewise were deployed in 

 polyethylene vials and likewise released odor at a rate 



of about 40 mg per day per tree. None of the vials were 

 replaced except ones with limonene, where vials were 

 renewed after 4 weeks. Dispensers of GA were replaced 

 after 5 weeks. 



A continuous perimeter row of apple trees about 

 220 yards long was selected in each orchard. Treatment 

 trees, all on the perimeter row, were about 30 yards 

 apart in order to separate treatments. Odors were 

 deployed on May 6-8 and remained until June 24-26. 

 Weekly beginning at petal fall (May 13-15), 40 fhiit 

 were examined per tree for evidence of fresh PC 

 egglaying scars. 



Results 



Results (Figure 1 ) show that trees baited with BEN 

 plus GA received significantly more fresh egglaying 

 injury than trees baited with GA alone, BEN alone or 

 trees without odor bait. Addition of ethyl isovalerate, 

 limonene, E-2-hexenal, Z-3-hexenyl acetate or hexyl 

 acetate did not significantly enhance the attractiveness 

 of BEN plus GA as an odor bait guiding PCs to trap 

 trees. Trees baited with BEN plus GA received about 

 15 times more PC egglaying scars than unbailed trees. 



Conclusions 



Our findings indicate that BEN plus GA represents 

 a potent combination of attractive odors whose use, in 

 both this study and the study reported in the preceding 

 article, culminates in an aggregation of PC egglaying 

 injury about 1 5-fold greater than that which occurs on 

 unbailed trees. Findings here further indicate that BEN 

 plus GA represents a synergistic odor combination 

 whose stimulating effects, as a combination, 



Fruit Notes, Volume 68, Winter, 2003 



11 



