Variations in chemical composition of birch foliage under air pollution stress and their consequences for Eriocrania miners.

The relationships between chemical composition of birch foliage, individual performance and population density of both solitary and gregarious species of Eriocrania leafminers (Lepidoptera: Eriocraniidae) were studied in the vicinity of the Harjavalta copper-nickel smelter, southwestern Finland. The contents of heavy metals (Cu, Ni, Fe and Zn) in birch foliage exponentially decreased with the distance from the factory whereas the content of manganese showed the opposite trend. Performance parameters of Eriocrania miners were correlated neither with the distance from the pollution source nor with the foliar content of heavy metals. However, larval masses of both solitary and gregarious species were highest at the zone of moderate pollution. The levels of total nitrogen and total carbon and the carbon: nitrogen ratio in birch leaves showed no clear patterns in relation to distance from the factory. Feeding efficiency of solitary larvae increased with higher foliar nitrogen content but decreased when the carbon: nitrogen ratio was high. Survival of solitary Eriocrania species was negatively correlated with total leaf carbon content. However, the population density of solitary miners showed a negative correlation with total foliar nitrogen and a positive correlation with the carbon:nitrogen ratio. Performance of the gregarious E. haworthi was not correlated with the chemical composition of birch leaves, whereas population density was highest close to the factory complex and correlated positively with the levels of copper and nickel in birch leaves. Consequently, pollution-induced changes in measured host plant chemicals were unlikely to affect population densities of Eriocrania miners via altered larval performance.