Effects of leaf maturity and wind stress on the nutrition of the generalist caterpillar Lymantria dispar feeding on poplar

Abstract

The growth rates of insect herbivores commonly decrease when they feed on mature leaves due to the combined effects of several nutritional and physiological mechanisms. Environmental stresses during leaf development may also decrease herbivore performance. The present study tests two main hypotheses to help clarify the importance of these factors for the nutrition and growth of an insect herbivore: (i) decreases in nutrient levels, consumption rates and nutrient assimilation efficiencies impact negatively on herbivores feeding on mature leaves and (ii) wind stress has a negative impact on herbivores feeding on mature leaves. The results show that mature poplar (Populus alba × Populus tremula) leaves have decreased levels of protein and increased levels of fibre, and that growth rates of gypsy moth (Lymantria dispar L.) are decreased on mature leaves in association with decreased consumption rates. However, in contrast to the first hypothesis, protein and carbohydrate are assimilated efficiently (74–82% and 84–87%, respectively) from immature and mature poplar leaves. The larvae are able to chew mature leaves as efficiently as immature leaves, potentially maximizing nutrient extraction. By contrast to the second hypothesis, wind‐stressed leaves have no significant detrimental effects on nutrient assimilation efficiencies, and the lower growth rates of L. dispar larvae feeding on mature wind‐stressed leaves can be explained by lower consumption rates. Therefore, the availability of nutrients to herbivores feeding on mature tree leaves is not necessarily impacted by lower assimilation efficiencies, even when leaves develop under wind stress. These results help explain some of the large variation between the nutritional qualities of trees for forest Lepidoptera.