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(Clem.), is an economically significant forest pest in Canada, for which improved control methods are sought. Nucleopolyhdrovirus use would be an improvement by reducing environmental impact, but is not commercially feasible due to high propagation cost and dose requirement. With a view to improving in vivo production techniques, spruce budworm larvae were infected at various doses and larval instars, and virus yield quantified. A diet plug bioassay was employed to allow larvae to be individually fed precisely controlled doses. Larval instars 4, 5 and 6 were infected with a wild-type nucleopolyhedrovirus, using doses between 10 and 106 virus occlusion bodies (OBs). Average yield per cadaver peaked at 4.3, 5.6 and 7.6 x 108 for fourth-, fifth, and sixth-instars, using doses of 103, 104, and 106 OBs respectively. At these doses 96, 96 and 68% of larvae consumed the diet plugs, to become infected. Our data suggest that, depending on the circumstance, e.g., limited available inoculum, larvae or labour, different infection strategies are preferable. However, OB potency variation between instars at harvest needs to be evaluated before confirming a propagation strategy. For each instar, feeding deterrence was observed above a theshold dose and may need to be considered in mass propagation strategies.
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