Response of the copper butterfly Lycaena tityrus to increased leaf nitrogen in natural food plants: evidence against the nitrogen limitation hypothesis.

This study examined the effects of increased leaf N in natural food plants on oviposition, preimaginal survival, growth, and adult size of the butterfly Lycaena tityrus. Female butterflies did not discriminate between leaves of high and low N content. In accordance with previous studies, we found higher growth rates and concomitantly decreased development times at a high N level. However, because of high pupal (and larval) mortality (overall 73.0%) as well as a reduction in adult size (by ca. 8%) this was, overall, not beneficial to the butterflies. Thus, our results were not consistent with the broad interspecific trend that insect herbivore performance is positively correlated with leaf N. These findings undermine the general applicability of the N limitation hypothesis. As the detrimental effects were largely confined to the pupal and adult stages, results obtained from the larval phase only may not yield reliable results and must therefore be interpreted with caution. If negative effects of N enrichment are found more frequently in declining species inhabiting nutrient poor grassland, this will have major implications for the conservation of these species.