Learning in two butterfly species when using flowers of the tropical milkweed Asclepias curassavica: No benefits for pollination.

Abstract

The ability of insect visitors to learn to manipulate complex flowers has important consequences for foraging efficiency and plant fitness. We investigated learning by two butterfly species, Danaus erippus and Heliconius erato, as they foraged on the complex flowers of Asclepias curassavica, as well as the consequences for pollination. To examine learning with respect to flower manipulation, butterflies were individually tested during four consecutive days under insectary conditions. At the end of each test, we recorded the number of pollinaria attached to the body of each butterfly and scored visited flowers for numbers of removed and inserted pollinia. We also conducted a field study to survey D. erippus and H. erato visiting flowers of A. curassavica, as well as to record numbers of pollinaria attached to the butterflies' bodies, and surveyed A. curassavica plants in the field to inspect flowers for pollinium removal and insertion. Learning improves the ability of both butterfly species to avoid the nonrewarding flower parts and to locate nectar more efficiently. There were no experience effects, for either species, on the numbers of removed and inserted pollinia. Heliconius erato removed and inserted more pollinia than D. erippus. For both butterfly species, pollinium removal was higher than pollinium insertion. This study is the first to show that Danaus and Heliconius butterflies can learn to manipulate complex flowers, but this learning ability does not confer benefits to pollination in A. curassavica.