Pre-ingestive effects of tannins on the spruce budworm, Choristoneura fumiferana (Clemens) (Lepidoptera: Tortricidae)

The spruce budworm, Choristoneura fumiferana (Clemens) (Lepidoptera: Tortricidae), is considered the most important pest threatening the coniferous forests of eastern North America. Its major hosts are balsam fir ( Abies balsamea ), white spruce ( Picea glauca ), red spruce ( Picea rubens ), and black spruce ( Picea mariana ), all of which contain defensive compounds including tannins. Tannins are known to act as feeding deterrents, digestibility reducers, and toxins in numerous insect species and specifically to reduce growth and survival in the spruce budworm. Using two-choice feeding tests, it was discovered that hydrolysable tannins act as a feeding deterrent and condensed tannins extracted from white spruce act as a phagostimulant for the spruce budworm. To my knowledge, this is the first time condensed tannins have been demonstrated to be phagostimulatory in any insect. It was shown that both types of tannins function via different mechanisms: spruce tannins directly stimulate feeding whereas tannic acid interferes with sucrose detection. A dose-response relationship was demonstrated for both types of tannin. Concentrations of defensive compounds and of tannins are affected by certain forest management techniques. Polar extracts from foliage sampled from 3 different thinning regimes were investigated for their affect on spruce budworm feeding, again using the two-choice feeding tests. Differences between trees appear to be more important than the effects of the thinning treatments but more data are necessary in order to make any firm conclusions. Tannin concentrations should be considered in forest management aimed at controlling spruce budworm populations