Avoidance of willows from moderately polluted area by leaf beetle, Melasoma lapponica: effects of emission or induced resistance?

Abstract

AbstractWe studied preference for willows along a pollution gradient on the Kola Peninsula, Russia, by the leaf beetle, Melasoma lapponica. Multiple tests with leaf disks demonstrated low preference for Salix borealis, S. caprea and S. phylicifolia from the plot situated 14 km from the smelter, in comparison with conspecific plants from plots situated at 1 and 29 km distances. This pattern was observed when testing beetles orginating from any plot both in 1993 and 1994, using both young and mature leaves of S. borealis. Although fumigation of S. borealis with realistic SO2 concentration (100 μg/m3) increased plant palatability, preference for plants from our study plots did not correlate with plot‐specific mean SO2 concentrations. Furthermore, no correlation with foliar concentrations of the main metal pollutants (Ni and Cu) was found. Palatability of plants was negatively correlated with population density of M. lapponica, which peaked in the moderately polluted plot 14 km from the smelter. Within this plot, beetles clearly preferred non‐damaged bushes of S. borealis to previously damaged bushes. We therefore conclude that low preference of S. borealis from the moderately polluted area was caused by plant resistance induced by severe damage from M. lapponica in previous years rather than by pollution impact. However, S. caprea and S. phylicifolia had little damage from M. lapponica, and low palatability of these species in the moderately polluted plot suggests changes in plant quality similar to changes in heavily damaged bushes of S. borealis.