Different tasks

A division of labor in social insects allows workers to specialize on food collection at a given time in their lives (Winston 1987), while solitary insects typically combine food-gathering with other tasks. Butterflies, beetles, and flies frequently intermix foraging, mating, and oviposition activities in a single flight or at a single location and time period (Faegri &

van der Pijl 1979; Dafni 1984; Stanton 1984; Young 1986; Eriksson 1994). Such "multi-tasking" may provide opportunities for interference or confusion of stimuli. Free-flying Colias butterflies, for example, showed decreased landing accuracy on oviposition host-plants after periods of nectar feeding, suggesting a tradeoffbetween the two searching modalities (Stanton 1984). Similarly, Pieris rapae butterflies that alternated nec-taring with oviposition flights switched among species of nectar plant significantly more often than did males or non-ovipositing females (Lewis 1989).

Solitary insects may reduce the problems of interference behaviorally, or via innate or learned responses. For butterflies, temporal segregation of feeding and oviposition flights may minimize opportunities for confusion of stimuli (Wiklund 1977; Dukas 1998). Context-dependent innate responses may also help solitary insects differentiate between separate behaviors. For example, nectar-feeding calliphorid and sarcophagid flies, which lay their eggs in dung and carrion, prefer yellow over brown-purple colored models in the presence of sweet scents, and the reverse in the presence of excremental scents (Kugler 1956). Similarly, exposure of Pieris butterflies to well-defined spectral regions elicits specific behaviors; e.g., insects extend their proboscides on blue and orange-red colors, and drum their tarsi on yellow-green (Scherer & Kolb 1987a). Such innate recognition systems may also serve as contextual triggers for learning (Gould 1984).

Differing energetic requirements will lead to different flower-visitation patterns

Energy requirements of pollinating insects also have important implications for their flower-visitation patterns. Because bees provision the nest for their young, they must collect more reward per unit time than do solitary insects, which generally forage only to meet their daily needs (Heinrich 1975). Metabolic energy costs of foraging and thermoregulation also vary between groups of pollinators; for example, bumble bees, which thermoregulate metabolically, will have higher energy requirements than will butterflies, which regulate their temperatures by basking (Heinrich 1975).

The high energetic requirements of social bees may select for "optimal" foraging rules that lead to efficient flower handling and predominately near-neighbor visits (Heinrich 1975; Pyke et al. 1977). Solitary pollinators, on the other hand, may remain on flowers for longer periods of time, fly greater distances between flowers, and visit fewer flowers in a given time period. Schmitt (1980), for example, found that bumble bees visiting Senecio (Asteraceae) flowers typically visit near-neighbor plants, while butterflies frequently bypass neighbors and fly significantly greater distances between plants. Such differing patterns of flower visitation may in turn affect parameters such as speed of learning, degree of interference between learned associations, duration of memory, and timing of transfer between short- and long-term memory (Greggers & Menzel 1993; see Menzel, this volume), all of which are virtually unexplored for non-hymenopteran insect pollinators.

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