NETTLE-FEEDING NYMPHALID BUTTERFLIES - TEMPERATURE, DEVELOPMENT AND DISTRIBUTION

1. Four nymphalid butterflies, Aglais urticae L., Inachis io L., Polyg onia c-album L. and Vanessa atalanta L., share the same primary host p lant, Urtica dioica L., but have different margins to their U.K, and E uropean ranges. Their developmental responses to a series of constant temperatures were measured. 2. Degree-day requirements were found broa dly to explain the relative distributions and differences in voltinism of A. urticae, P. c-album and I. io. The migrant V. atalanta did not fit into the predicted pattern, and this species may be more limited b y its ability to overwinter. 3. Although the most northerly distribute d species, A. urticae, had the lowest degree-day requirement, it had t he highest developmental threshold and performed best (for mortality, pupal weight and relative growth rate) at high experimental temperatur es. It is suggested that this may be due to the gregarious nature of i ts larvae and their possible ability to thermoregulate. 4. At southern margins, different distributional limits may be explained partly by l arval gregariousness (a more northern trait) and maximum temperatures at which development is possible. 5. Limits to the distributions of th ese mobile species are at least partially explicable by the interactio n of climatic patterns and thermal biology A rapid response to climate change is predicted, and has already been observed in two of the spec ies.