Spatial Distribution of Plum Curculio 

 Egglaying in Apple Trees 



Jaime Piiiero, Katie Bednaz, Amanda Ross, and Ronald Prokopy 

 Department of Entomology, University of Massachusetts 



Determining the distribution of mitial and sub- 

 sequent plum curculio (PC) damage inflicted upon 

 fruit within host tree canopies could aid in opti- 

 mal placement of traps for monitoring PC, espe- 

 cially placement of branch-mimicking cylinder 

 traps. Such knowledge may also aid in devising 

 sound protocols for monitoring sectors of host trees 

 most prone to receiving PC damage. Studies per- 

 formed in past years (nearly all in Quebec and pre- 

 dominantly with caged trees) have yielded valu- 

 able but somewhat inconsistent results (perhaps 

 due to differences in tree size, tree phenology, or 

 adult PC population density). It has been found, 

 for example, that PC damage is greatest at tops of 

 large apple trees, but for semi-dwarf caged trees, 

 PC damage has been reported as concentrated to- 

 ward the center of the canopy. Here, at approxi- 

 mately one-week intervals in 2000, we compared 

 the spatial distribution of PC infestation of fruit of 

 small, medium, and large apple trees. 



Materials & Methods 



EXTERIOR ZONE 



Figure 1 . Representation of the subdivision of an apple tree 

 canopy into three levels, showing the four limb orientations, 

 and the exterior and interior zones of tree branches (only for 

 medium and large trees). Twenty-four sampling points were used 

 for medium and large trees and 12 for small trees. 



Studies were conducted in unsprayed sections 

 of two apple orchards (Horticultural Research Center and 

 Atkin's Farm) located in Belchertown, MA. At the HRC, we 

 sampled from six small (Mclntosh/M.9) and four medium 

 (Priscilla/M.26) trees. At Atkin's we inspected the fruit of 

 six large (Cortland/M.7) trees. We divided tree canopies into 

 bottom, middle, and top (vertical plane) sectors by selecting 

 and markini; branches at each level. Within each level, there 



were four branches, one each pointing West, South, North, 

 and East. Each of the 12 branches per tree was in turn subdi- 

 vided into an external and internal zone, except for small 

 trees where (because of limited canopy breadth) fruit in- 

 spection was confined to the mid part of tree branches. This 

 approach provided 24 sampling locations in large and me- 

 dium trees and 12 sampling locations in small trees (Figure 



36 



Fruit Notes, Volume 65, 2000 



