honeybees, and Pieris butterflies, floral handling time decreases as pollinators gain experience in accessing rewards from a given plant species, and often increases when the pollinator switches to a new species (Heinrich 1979; Lewis 1986, 1993; Laverty 1994; Goulson et al. 1997). Lewis (1993) suggested that flower morphology can be seen as shaped in part by the advantages conferred when a pollinator must make a substantial investment in learning to handle a flower. She posited that plants should evolve to attract generalist pollinators, which then become facultative specialists based on "training" by the flower (Lewis 1993).

Floral color change

Plants take advantage of pollinators' color-learning ability by producing flowers that change color to provide accurate indications of reward status. Flowers in over 80 angiosperm families undergo localized or whole-flower color changes that are highly correlated with nectar and pollen availability; pre-change flowers are rewarding, but post-change flowers are not (Gori 1983; Weiss 1991, 1995; Weiss & Lamont 1997). Beetles, flies, moths, butterflies, and bees preferentially visit variously colored pre-change flowers even if they are in the minority in a floral display (Gori 1983; Weiss 1991, 1995; Weiss & Lamont 1997). A learned association between floral color phase and nectar availability has been explicitly demonstrated for butterflies (Weiss 1995, 1997), and is likely for bees and flies. Beetle-pollinated color-changing flowers are not common (Weiss 1995; Weiss & Lamont 1997), and it is possible that beetles could be guided to pre-change flowers by innate attraction to particular odors or colors, rather than by the more flexible learned response that seems to characterize visits by other pollinators (Weiss 1995).

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