RESPONSE OF THIRD-, FOURTH-, FIFTH-, AND SIXTH-INSTAR SPRUCE BUDWORM, CHORISTONEURA FUMIFERANA (CLEM.), LARVAE TO NUCLEAR POLYHEDROSIS VIRUS

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Abstract
Four different types of insect viruses have been isolated from the eastern spruce budworm, Choristoneura fumiferana (Clem.), but most research efforts have been concentrated on developing the nuclear polyhedrosis virus (NPV) as a viable control agent (Cunningham 1985). There are no published reports of LD50 values for this important forest pest. Recently, a LC50 of 483 viral polyhedra per square millimetre of diet surface for fifth-instar budworm larvae was determined using surface contamination feeding techniques (Cunningham et al. 1983). Because the dosages used in efficacy trials are derived from laboratory LD50 values, experiments were conducted to determine the virulence of this NPV to eastern spruce budworm. Bioassays were conducted with all feeding instars. Reported here are values for the LD50 dosages for third-, fourth-, fifth-, and sixth-instar spruce budworm larvae.