The Spruce Budworm and the Spruce Coneworm: Behavior on Red Spruce and Insecticide Efficacy
- Spies, Charles J. III
- Stratton, Robert D.
A study of the feeding and concealment behaviors of spruce budworm, Choristoneura fumiferana (Clem.), and spruce coneworm, Dioryctria reniculelloides (Mutuura and Munroe), on red spruce, Picea rubens (Sarg.), was conducted in Maine in 1984. Also, the efficacy of two aerial insecticide treatments to red spruce was evaluated for both insects.
Direct observations were made on untreated caged and "wild" insects during the last two larval instars (budworm L5-L6, and conworm L4-L5). Indirect observations were made during larval stages L3-L6 of budworm and coincident L2-L5 of coneworm on branch samples pole-pruned from three sample line replicates whitin a Bacillus thuringiensis (B.t.) spray block, a Zectran spray block and an untreated control block. Branches were frozen soon after collection and examinations were made under laboratory conditions.
Results show that feeding and concealment behaviors were similar for both species. Caged budworm and coneworm destroyed an average of 9.4 and 9.0 buds respectively. Attack by either species most often led to functional bud destruction from severing of the central bud stem. The number of buds attacked in all treatment areas increased significantly after budworm and coneworm reached peak fourth and third instars, respectively. Thirty to forty percent of the larvae were concealed during all sample periods, usually entirely within vegetative or flower buds.
In the study areas neither species was effectively controlled on red spruce. However, these results are not representative of the entire spray project as both BT and Zectran did provide better results on other operational spray blocks.
Intensive laboratory observations made on branch samples show that standard field defoliation measurement techniques used on fir underestimate damage on spruce by one-half.
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