The Wood White Butterfly Leptidea sinapis and Its Nectar Plants: A Case of Mutualism or Parasitism?

Abstract

The purpose of this study was to determine (1) the nectar plant utilization of a population of Leptidea sinapis L. by following individual adults in their natural habitat, and (2) whether L. sinapis pollinates the flowers visited by collecting insects immediately after their visiting flowers and identifying pollen grains on the proboscis, palpi, head and thorax. Approximately 90% of the flower visits were made to Viola canina, V. riviniana and Lathyrus montanus. Although the strong flower preference exhibited by L. sinapis would make it a suitable pollinator, it seems unlikely that any flowers were pollinated by the butterflies in view of their low pollen load (im = 3.0 grains/specimen). Thus, L. sinapis should be regarded as a parasite on its nectar plants. Since the feeding behaviour of L. sinapis is typical of most butterflies we advance the tentative hypothesis that butterflies as a group may have evolved to occupy a parasitic mode of life as adults, feeding on the nectar of flowers without pollinating them. If so the evolution of the long pliable proboscis of butterflies may have opened a whole new feeding niche for adult butterflies by making accessible not only the exposed nectar from unspecialized flowers but also the formerly hidden nectar from a vast variety of bee and bumblebee flowers. However, since the above hypotheses are based on little evidence from but one butterfly species a broad study is needed to test their validity.