Fig. 11.4. The number of tobacco budworms (Heliothis virescens) captured by paper wasps (Polistes arizonensis) on the two host-plants, sunflower (Helianthus annuus) and groundcherry (Physalis pubescens) on eight different days. The two host-plant species were set up in a paired-choice test with one caterpillar on each; data from 20 wasps were recorded on each day. Capture rate was significantly different between the two host species (p < 0.001). (Figure from Geitzenauer & Bernays 1996.)

1988) foraging efficiency. Furthermore, Minckley et al. (1994) suggested that synchronization between a specialist bee and its host flower was a key factor justifying specialization. Yet predation may also have played a role in selecting for specialization. Bernays (1989; Bernays & Graham 1988) suggested that herbivorous insects with greater host-plant breadth were more vulnerable to generalist predators; similar effects might influence diet breadths of pollinators. At the least, specialist bees may possess innate escape movements that are most efficient for their specific host flower and allow higher escape rates from predators than on other flowers. In addition, the specialization on one plant species may have been in part due to less predation on that species.

Experience with a single plant species may allow individual generalist pollinators to perfect inter-flower and inter-plant movements, to become more familiar with the flowers and hence more likely to notice ambushing predators, and to acquire refined escape movements. These may reduce predation risk for flower-constant individuals.

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