The decline and current distribution of Parnassius apollo (Linnaeus) in Finland; the role of Cd

We tested two hypotheses that assume aspects of host-plant quality restrict the current distribution of Parnassius apollo. The “foreign host-plant hypothesis” states that host plants from outside the current range of P. apollo are, for some reason, unsuitable for the developing larvae. The “heavy-metal hypothesis” specifically attributes this unsuitability to a higher concentration of heavy metals (especially Cd) outside the current species’...