Abstract
The larvae of jack pine budworm, Choristoneura pinus pinus Free., were reared individually on diet in the laboratory. Observation of ecdysis and measurement of the corresponding head capsules identified seven distinct instars. Parasitism by the common larval parasitoid Apanteles fumiferanae Vier. resulted in smaller head capsule size and retarded development during the fourth, fifth, and sixth instars of the jack pine bud worm.