Document: MAR-3-43-7

Host plant selection in a guild of cactus-specialist bees: Pollen preferences of females foraging for larval provisions.

MCINTOSH, M.E.*

University of Arizona, Tucson AZ 85721 U.S.A. ¹

Abstract:
Empirical studies of host plant selection by herbivorous insects continue to provide evolutionary biologists with important insights into the forces that shape species interactions. In particular, investigating the host range of different insect herbivores that specialize on the same plants can reveal much about the products of convergent evolution, and can also suggest the future trajectories of the evolutionary process. Specializing on cactus pollen for larval provisions has arisen independently in several bee lineages. I tested the pollen specificity of four species of these bees (Diadasia rinconis, Diadasia opuntiae, Lithurge apicalis, and Idiomelissodes duplocincta) by offering them cactus flowers in which the cactus pollen had been removed and replaced with other kinds of pollen. Trials were performed on free-flying bees in the field (D. rinconis, L. apicalis, and I. duplocincta), and in a field-based flight cage with marked individuals (D. opuntiae). Bees were give a multiple choice assay which always included cactus pollen as one of the choices. I found that in the populations tested, there were individuals of both species of Diadasia that were willing to collect novel pollen, especially pollen from Sphaeralcea (globe-mallow) flowers, which is the ancestral host for the genus Diadasia. I also found a surprising level of individual variation in foraging preferences among the marked individuals of D. opuntiae. Individuals of I. duplocincta accepted pollen from only one non-cactus host, whereas individuals of L. apicalis rejected all non-cactus pollen. These results suggest that some populations of both species of Diadasia might contain individuals that have the potential to shift to new hosts, or to revert to the ancestral host, and also reveal that the products of convergent evolution can be quite diverse.

Keywords: Plant-insect interactions, bees, specialization, pollen, host-shifts, Cactaceae, foraging behavior

This abstract is being presented at: 9:00 AM in session:
Oral Session #4: Herbivore Responses to Plants.