PARENT SESSION
Poster Session 34: Herbivory
Thursday, August 11, 5:00 PM - 6:30 PM, Exhibit Hall 220 A-E, Level 2, Palais des congrès de Montréal
Aphid movement and acclimation to host plant quality: Implications for the effects of host plant variation on herbivore population dynamics.
Underwood, Nora1, Halpern, Stacey*,1, 1 Department of Biological Science, Tallahassee, FL, USA
ABSTRACT- Variation in host plant quality can affect herbivore population dynamics. We explored two mechanisms, herbivore movement and acclimation, that may contribute to these effects in the interaction between wild strawberry (Fragaria chiloensis) and its specialist aphid (Chaetosiphon fragaefolii). We examined the effects of host-plant genotype and variance among host-plant genotypes on movement rates of apterous aphids in the field and greenhouse. In the greenhouse, we followed the movement of individual aphids in plant arrays of one or three different genotypes. Aphids showed no taxis toward particular plant genotypes but left different plant genotypes at different rates. They tended to move more among plants in three-genotype arrays (with a variety of plant genotypes) than expected from their movement in single-genotype arrays. In the field we estimated aphid movement rates over several years on experimental populations of either one or two plant genotypes. Aphid movement differed among plant genotypes, but not between plant populations with different numbers of genotypes. Movement rate in the field was also influenced by aphid population size. In both the greenhouse and the field, aphids tended to move more from plant genotypes that were of higher quality as food for the aphids. Our movement results suggest that dispersal among plants by strawberry aphid apterae is affected by individual plant characteristics and possibly by the variety of plants in the vicinity. We examined the effect of acclimation to host plant genotype on aphid fecundity in the field. We reared aphids on three host plant genotypes, and compared their fecundity when moved to the same or a different destination genotype. Prior host plant genotype strongly affected aphid fecundity across all destination genotypes. However, neither the current genotype nor switching between genotypes influenced aphid fecundity. When herbivore movement is non-random, as it is in this system, persistent effects of prior host plant quality could contribute to the effects of variation on insect population dynamics. Together, these results suggest that strawberry aphid populations should be influenced both by average plant quality and by variance in plant quality within a population.
Key words: heterogeneity, insect herbivores, Chaetosiphon fragaefolii, Fragaria chiloensis