Within-Tree Distribution of Phyllonorycter blancardella (F.) and P. crataegella (Clemens) (Lepidoptera: Gracillariidae) and Associated Levels of Parasitism in Commercial Apple Orchards

The within-tree distribution of Phyllonorycter blancardella (F.) and P. crataegella (Clemens) and the associated levels of parasitism in commercial apple orchards were examined for 2 years at two sites in west-central Missouri. Canopies of 10 trees at both sites were divided into three regions (or heights): upper, middle, and lower. Each region was further divided into within-row and between-row positions. Leaf and mine samples were taken at the end of every leafminer generation to determine mean leafminer density (mines/leaf) and percent parasitism. Neither the leafminers nor the parasitoids displayed a preference for either the within-row or between-row canopy positions of the tree. However, at both sites and years, the mean level of mines/leaf was generally greater in the lower-middle canopy regions of the tree. Conversely, parasitoid activity appeared to be more evenly distributed throughout the tree with a tendency for higher levels of parasitism to be found in the middle-upper canopy regions. Early-season monitoring of leafminer and parasitoid activity can be accurately determined with leaf samples gathered from the lower portion of the canopy.