Between-species differences in heavy metal levels in four pine diprionids (hymenoptera) along an air pollutant gradient.

The concentrations of copper, iron, nickel and cadmium were studied in cocoons of four pine sawfly species, viz. Gilpinia virens, G. frutetorum, Microdiprion pallipes and Neodiprion sertifer. Larvae were reared in the laboratory on needles of Scots pine collected along a pollution gradient around a copper smelter in SW Finland. Heavy metal concentrations in all the species and needles decreased with increasing distance from the pollution source in accordance with linear regression models. Metal levels were highest in M. pallipes and lowest in G. virens, being only about one half to one quarter of those in M. pallipes. Concentrations of copper, iron and nickel in the insects were lower than in their food. Cadmium bioaccumulated in N. sertifer, G. frutetorum and, especially, in M. pallipes. The differences in these closely related pine defoliators are comparable to those between different trophic levels or species with entirely different feeding characteristics.