Effects of synthesized tannin on the growth and survival of a generalist herbivorous insect, the common cutworm, Spodoptera litura Fabricius (Lepidoptera: Noctuidae)

We examined the effects of tannin on a generalist herbivorous insect, the common cutworm (Spodoptera litura). The dosage effect was estimated by measuring the growth performance of the cutworm when the larvae were fed artificial diets containing different amounts of synthesized tannin. We used artificial diets to exclude the effects of non-tannin defense mechanisms in plant foliage. Indices of growth performance, number of dead larvae, pupal weight, total feeding amount and length of larval period were obtained. We found that tannin inhibited the growth of the cutworm larvae and that the inhibitory effect was proportional to the amount of tannin ingested. These results support the traditional theory that plant tannin is a defense agent against generalist herbivores, and that its effects are proportional to its concentration in foliage.