23 and May 30 for medium trees, and May 24 and 

 May 31 for small trees. Each mdividual fruit was 

 categorized as injured or uninjured based on the 

 presence or absence of PC egglaying scars (fresh or 

 old), and its diameter was recorded. To assess the 

 relationship between fruit size and occurrence of injury 

 to fruit by PC, comparisons of the diameter (in mm) of 

 fruit having or lacking PC scars were performed. 



Results 



Figure 1 clearly shows that, regardless of tree size, 

 fruit sampled early in the season that showed PC injury 

 were significantly larger than uninjured fruit. The 

 smallest size of a fruit having a PC scar was 4.8 mm in 

 diameter, which corresponded to the first sampling date 

 in small Mcintosh trees. 



Conclusions 



trees where fruit are larger (e.g., upper part of the 

 canopy of large trees, exterior zone of branches). As 

 the season progresses, however, it is likely that smaller 

 fruit may be more likely to be attacked by PC, possibly 

 because, as suggested by Levine and Hall ( 1 977), late- 

 season mortality of PC larvae is greater in large fruit 

 due to the higher internal pressure of the growing cells. 

 None of the trees in our study was baited with attractive 

 odor. Results on the distribution of PC injury among 

 fruit in various tree sectors could be different for odor- 

 baited trap trees. 



A cknowledgnients 



This study was supported with funds provided by a 

 USDA Northeast Regional IPM grant, a Hatch grant, 

 a grant from USDA Crops at Risk program, and the 

 New England Tree Fruit Research Committee. 



Our findings lead us to conclude that, early in the 

 season, larger fruit are much more prone to attack by 

 PC than are smaller fruit, probably because abscission 

 of fruit damaged by PC is more likely to occur when 

 fruit are small. Thus, early-season sampling of unbailed 

 trees should be conducted preferentially in areas of the 



Literature Cited 



Levine, E., and Hall, F.R. 1977. Effect of feeding and 

 oviposition by the plum curculio on apple and plum fruit 

 abscission. Journal of Economic Entomology 70: 603- 

 607. 



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Fruit Notes, Volume 69, Winter, 2004 



17 



