The possibility that uneven within-tree feeding patterns by jack pine budworm (Choristoneura pinus pinus Freeman) larvae could be related to underlying variation in host jack pine (Pinus banksiana Lamb.) foliar water, nutrient, and monoterpene contents was considered. Choristoneura pinus pinus feeds disproportionately in the upper portion of the canopy and almost exclusively on the basal portions of needles. Within needles, the distribution of water, several nutrients, and monoterpenes varied significantly between the distal and basal sections. Water, nitrogen, sulfur, manganese, and zinc levels occurred in higher concentrations in the distal section of the needle, which would not be predicted based on C. pinus pinus feeding patterns. Phosphorus, potassium, calcium, iron, and copper were significantly higher in the basal section. Although the latter differences might be predicted based on C. pinus pinus feeding patterns, they were not strong (ranging from 7.8% to 36.4% relative differences, as compared with 10.7%-50.0% relative differences in the former group). By contrast, concentrations of foliar monoterpenes were more strongly associated with known feeding patterns of C. pinus pinus. These relative differences ranged from myrcene (26.8%) to limonene (44.79%). Thus, foliar differences affecting within-needle feeding selection appear more associated with allelochemicals than nutrients or water. In contrast with the within-needle associations between larval feeding and foliar chemistry, no associations between upper and lower canopy foliage were observed. Water, nutrients, and monoterpenes were evenly distributed across the upper and lower canopy locations. Thus, differential feeding between canopy locations cannot be explained by foliar constituents. Rather, it is more likely explained by other environmental factors, such as proximity to and density of reproductive and vegetative shoots.
The ecological interaction of the mountain pine beetle and jack pine budworm in the boreal forest
