Effects of Air Pollution on Host Plant Quality, Individual Performance, and Population Density of Eriocrania Miners (Lepidoptera: Eriocraniidae)

We estimated correlations between birch foliage quality, individual performance, and population density of Eriocrania miners in southwestern Finland around a factory complex emitting large quantities of sulphur dioxide and heavy metals. The study area included 13 sites in different directions and at varying distances (0–11 km) from the pollution source. As an indicator of foliage quality, we used the ratio between the final larval mass and mass of frass produced during the whole larval time and interpreted a high ratio to mean high-quality diet. The highest quality of birch foliage and the highest larval masses were found at the zone of moderate pollution based on levels of heavy metals in birch leaves. Population density was not correlated with the distance from the pollution source either in 1991 or 1992. Changes in miner density from 1991 to 1992, but not density as such, correlated positively with birch foliage quality for the parental generation in 1991. Therefore, although foliage quality modified the density, site-specific abundances of miners were affected strongly by other factors. Heavy metal concentrations of leaves may function as a factor because they correlated negatively with population density of Eriocrania .