Tree species effects on Btk control of spruce budworm

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Spruce budworm is the most damaging forest pest in eastern North America, and is currently undergoing anoutbreak, with severe defoliation in Quebec spreading into New Brunswick. Current efforts to control sprucebudworm involve spraying with novel biological insecticides, which (compared with chemical agents usedagainst past outbreaks) have enormously reduced non-target toxicity. However, we are still learning how to usethese agents effectively and efficiently. We will work to understand the relative effectiveness of one biologicalinsecticide, Btk, on the two major host trees of spruce budworm in northern NB and Quebec: balsam fir andblack spruce. Btk spray settles on tree foliage, where it is ingested by feeding budworm larvae. Because thetwo trees differ in branch and needle architecture, and also in quality as food for developing larvae, Btk may beingested, and may work, differently on budworm feeding on each tree. We will measure budworm mortality onthe two tree species, and in forest stands differing in species composition, comparing stands treated with Btk tountreated stands. This will let us design Btk application strategies to control budworm effectively, in a forestmosaic of variable species composition, while using a minimum of insecticide.