Vision and learning in some neglected pollinators beetles flies moths and butterflies

Ask a member of the general public what kinds of insects pollinate flowers and chances are she'll say bees. Certainly hymenopterans pollinate a tremendous variety of plant taxa, and honeybees and bumble bees in particular are economically important and visible pollinators (McGregor 1976; Buchmann & Nabhan 1996; Proctor et al. 1996). However, studies of social bees have long dominated academic and applied pollination arenas (Lindauer 1963; von Frisch 1967; Menzel 1967), to the relative neglect of other taxa. Insects in three major orders, Coleoptera, Diptera, and Lepidoptera, are key pollinators of a broad range of angiosperm taxa (Kevan & Baker 1983; Proctor et al. 1996), but in comparison with bees, much less is known about their effectiveness as pollinators, or about the sensory attributes and learning abilities that guide their behaviors. This lack of study has several causes, including the lesser importance of non-hymenopteran insects as pollinators of crop plants (notwithstanding their role in pollination of mangos, cacao, papayas, parsnips, pomegranates, carrots, and onions; McGregor 1976), their relative infrequency as major pollinators in European and North American systems (Johnson & Steiner 2000), and the difficulty in raising and studying solitary rather than social insects.

Further study of these neglected pollinators will help us to understand the breadth and diversity of insect sensory systems and learning abilities. We might expect that beetles, flies, moths, and butterflies would have much in common with bees, based on the monophyly of Insecta and the common dependence of all anthophilous insects on flowers, which should subject them to similar selection pressures. We might also expect a number of differences both across and within taxa, given the independent evolutionary histories of Coleoptera, Diptera, Lepidoptera, and

Hymenoptera, and the attendant differences in each group's lifestyles.

Investigation of the sensory capacities and learning abilities of non-hymenopteran insects will also help to elucidate the pathways by which flowers have evolved. Although angiosperms appear in the fossil record at least 130 million years ago (Ren 1998; Sun et al. 1998), eusocial hymenopte-rans are relatively late arrivals evolutionarily, appearing somewhere between 40 and 80 million years ago (Michener & Grimaldi 1988; Poinar 1994). Thus other pollinating insects, including beetles, flies, butterflies, moths, and non-social bees, some of which antedate angiosperms in the fossil record (Crepet & Friis 1987; Ren 1998), have undoubtedly played an important role as agents of natural selection on floral features.

In this chapter, I focus on vision and learning in flower-visiting coleop-terans, dipterans, and lepidopterans. I briefly review what is known about their performance as pollinators, the senses they use to locate flowers, their color vision and innate color preferences, and finally their learning ability. I then discuss some important lifestyle characteristics that affect flower visitation patterns and thus have implications for differences in the aforementioned traits. I conclude with some open-ended questions that I hope will suggest directions for future research on these neglected pollinators.

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