Nectar Production and Flower Visitors of Asclepias verticillata

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Abstract
A. verticillata is self-incompatible and can propagate vegetatively. Nectar is produced mainly between 1800-2200 h, throughout the 4-5 day life of the flower. Insect visitations at this time were infrequent on all 4 study sites, a seemingly anomalous situation. Most pollinia vectors visited the flowers during the day. The most frequent vectors were Hymenoptera, especially wasps and honeybees, and lepidoptera, especially wasps and honeybees, and Lepidoptera, especially moths and the introduced cabbage white butterfly. Most flower-visiting insects were nectar thieves, carrying no pollinia. None of the potential pollinators seem to be closely coevolved, morphologically or seasonally, with the flowering of A. verticillata. The probability of an individual flower being visited by a potential vector is very low, corresponding to the observed low percentage of pod set, but between-site differences in composition of the vector fauna (proportional similarities less than 36%) and rates of visitation were not correlated with differences in levels of fruit production.

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