Effects of host plant quality on overwintering success of the leaf beetle Chrysomela lapponica (Coleoptera: Chrysomelidae)

I investigated effects of density-dependent variation in host plant quality on adult feeding and overwintering success of the leaf beetle Chrysomela lapponica L. During pre-overwintering period adult beetles were fed in the laboratory on host plants, Salix borealis, originating from (a) a site with low density population of C. lapponica, (b) a site with peak density of C. lapponica, and (c) a post-outbreak site. Beetles fed on plants from low density and peak density sites demonstrated similar performance, whereas on plants from post-outbreak site beetles fed longer, gained more weight, and experienced greater mortality during overwintering. Higher water content in these beetles suggests that the main reason for increased winter mortality is insufficient dehydration of the beetles' bodies, presumably due to low quality food. The total carbon concentration in host plant foliage explained variation in most beetle performance indices, while total nitrogen did not correlate with beetle performance. Damage-induced decrease in quality of host plants from post-outbreak sites (delayed inducible resistance, DIR), associated with increase in carbon-containing defensive compounds, was earlier found to increase larval mortality and thus contribute to the decline in population density of C. lapponica. Results of the current study suggest that DIR can also disturb pre-overwintering feeding and thus increase winter mortality of adult beetles, enhancing post-outbreak density decline.