Inflorescence Choice and Time Allocation by Insects Foraging on Milkweed

Abstract

Bumble bees (Bombus spp.), honey bees (Apis mellifera) and other insects visited milkweed (Asclepias syriaca) inflorescences (umbels) roughly in proportion to the number of nectar-producing flowers on them. On stems with high-quality, middlequality, and low-quality umbels (25+, 5-10, 0 nectar-producing flowers), insects foraged longer and visited more flowers on high-quality umbels than on middle-quality ones. However, they visited nectar-producing flowers with similar frequency and processed flowers at a similar rate on both high-quality and middle-quality umbels, suggesting an ability to track the nectar resources closely. Very few insects visited lowquality umbels. Most insects that foraged on both of these umbels visited the highquality umbel first, apparently a consequence of its condition, rather than its position on a stem. Thus, the quality of the first umbel visited influenced the decision of whether to visit another umbel on the same stem.