FIGURE 3.

Taxifolin and catechin are defense compounds in Norway spruce that act against both bark beetles and an associated fungus. (A) E. polonica grew significantly slower on potato dextrose agar amended with 2 mg ml^-1 catechin, 2 mg ml^-1 taxifolin, or a 2 mg ml^-1 mixture of catechin and taxifolin (2:1) (n = 4; error bars = SE; p < 0.001). (B) Ips typographus tunneled significantly further into bark medium containing 1 mg m^-1 catechin or unamended medium compared to medium with a 1:1 catechin-taxifolin mixture (n = 15; error bars = SE; p < 0.001). (C) Bark beetles gained more weight feeding on unamended bark medium without flavonoids than on medium amended with 1 mg ml^-1 catechin, taxifolin, or both (n = 15; error bars = SE; p < 0.05). Different letters refer to statistically significant differences at p < 0.05.