The spruce budworm Choristoneura fumiferana is an important defoliator of coniferous forests of North America and primarily attacks balsam fir and white spruce. Sylvicultural thinning techniques have been shown to directly affect the success of the spruce budworm by disturbing foliar biochemistry. More specifically, the first year after a selective cut, the remaining trees grow vigorously but experience a decrease in certain defensive compounds, such as monoterpenes and tannins, resulting in trees that are more susceptible to spruce budworm attack. We combined behavioural and electrophysiological techniques to better understand the relationship between sylvicultural thinning, tannins, and the spruce budworm. Two-choice feeding tests with 6th instar larvae have revealed a preference for solutions of spruce tannins (condensed tannin) in 25 mM sucrose to 25 mM sucrose alone. However, larvae prefer the sucrose solution to solutions of tannic acid (hydrolysable tannin) in 25 mM sucrose. These preferences remained regardless of tannic acid concentration in the rearing diet. Feeding rate was reduced by high concentrations of tannic acid or tannin. Electrophysiologically, solutions of tannic acid alone failed to produce a response on any of the gustatory sensilla tested. Tannic acid appears to play a modulatory or peripheral role by interacting with the taste receptors or the sucrose itself to inhibit tasting of this sugar.