Decrease in feeding niche breadth of Melasoma lapponica (Coleoptera: Chrysomelidae) with increase in pollution

We studied host-plant preference and performance of the leaf beetle, Melasoma lapponica, around Severonikel smelter situated in Monchegorsk, Russia. The breadth of feeding niche (Smith's measure) based on both field counts and preference tests decreased with an increase of ambient SO₂ concentration, but showed no relationship with either metal pollutants or beetle population densities. In heavily polluted plots (mean annual SO₂ concentrations 400-1000 μg/m³) the beetles concentrated on Salix borealis, Whereas in moderately and slightly polluted plots they used other willow species as well. No difference in survival was revealed between M. lapponica fed with leaves of S. borealis from heavily and sloghtly polluted plots. However, performance of larvae fed with Salix caprea and S. Phylicifolia was significantly lower when leaves were collected from heavily polluted plots. In these plots beetles clearly preferred S. borealis, the only species assuring high survival of M. lapponica under strong pollution impact. Decrease in preference of two less favourable hosts, S. caprea and S. phylicifolia, with increase in pollution can therefore be considered as an adaptive response of M. lapponica to pollution-induced changes in host-plant quality.