Proboscis morphology and food preferences in nymphalid butterflies (Lepidoptera : Nymphalidae)

Many species of nymphalid butterflies only exceptionally visit flowers and feed instead on tree sap, juice of rotting fruits and other decaying substa nces. To investigate whether the proboscis morphology of these non-flower-v isiting Nymphalidae differs from that of nectarivorous butterflies, represe ntatives from 64 nymphalid species with known feeding preferences were exam ined. Morphometric comparison of the proboscis revealed characteristic diff erences in proboscis length, tip-region length, wall composition, and numbe r and shape of proboscis sensilla between these two feeding guilds. The inv estigated non-flower-visiting species belonging to Apaturinae, Limenitidina e, Morphinae, Brassolinae, Nymphalinae and Satyrinae, possess a relatively short and light-coloured proboscis which has a long tip-region with a great number of club-shaped sensilla styloconica. Densely arranged, these sensil la form a flat brush located laterally from the openings into the food cana l on the dorsal side of the tip-region. Among the non-flower-visiting speci es, a second type of proboscis was found in fruit-feeding Charaxinae the st out tip-region of which is equipped with more widely spaced sensilla styloc onica. The investigated flower-visiting Heliconiinae, Nymphalinae, Satyrina e, Danainae and Ithomiinae are characterized by a slender, darker-coloured proboscis with a rather short tip-region bearing fewer sensilla styloconica in a loose arrangement. Discriminant analysis revealed that the tip-region length, the number of sensilla styloconica and the relative proboscis leng th are the most important discriminating variables between the flower-visit ing and the non-flower-visiting species. The proboscis morphology of nympha lid butterflies corresponds with certain feeding habits and allow us to mak e predictions on their food preferences. The 'brush-tipped' proboscis seems to have a functional role in the accumulation of fluid and the uptake of l iquid from wet surfaces such as rotting fruits or tree sap. We conclude fro m the phylogeny of the examined taxa that this derived proboscis lip morpho logy evolved several times independently as an adaptation to the exploitati on of new food resources.