Biological performance of the white pine weevil in relation to the anatomy of the resin canal system of four different host species

The anatomy of the resin canal system was observed on lateral branches of four host species of the white pine weevil (Pissodes strobi Peck) in relation to weevil performance. The host species studied were Norway spruce (Picea abies (L.) Karst.), white spruce (Picea glauca (Moench) Voss), red spruce (Picea rubens Sarg.), and white pine (Pinus strobus L.). Survival, number, and mass of adult weevils were measured on attacked terminal leaders collected before adult emergence. One uppermost lateral branch was collected at the base of each attacked leader. Cross sections of these lateral branches were observed to measure the number, diameter, depth, and density of inner and outer resin canals. Nearly all resin canal measurements differed significantly among species, with white pine differing greatly from the other species with larger canals and lower canal density. Correlation analysis demonstrated that the anatomy of the resin canal system was principally related to adult mass, with the most important variable being the density of inner canals (r = –0.54). Trees characterized by low density of large inner resin canals, like white pine, seemed to favour mass gain in adult weevils. The present study suggests that a high density of inner resin canals constrains the insect to feed on canals early in larval development, which subsequently reduces weevil mass.