Submitted to: Ecological Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 30, 2010
Publication Date: May 13, 2010
Citation: Tipping, P.W., Martin, M.R., Bauer, L., Center, T.D. 2010. Asymmetric impacts of two herbivore ecotypes on similar host plants . Ecological Entomology, Vol. 35, Issue 4, pp. 469-476. Interpretive Summary: The weevil Cyrtobagous salviniae feeds on a number of different species of Salvinia, which are exotic floating ferns. Two weevil ecotypes (Brazil and Florida) were evaluated on Salvinia molesta (giant salvinia) and S. minima (common salvinia) biomass production, coverage, and nutrient dynamics in a series of laboratory and outdoor tank experiments. In the laboratory, feeding by the larger-sized Brazil ecotype reduced the biomass production of the larger S. molesta by 25.9% but not that of the smaller S. minima, which increased 33.2%. Herbivory by the smaller-sized Florida C. salviniae ecotype reduced S. minima biomass by 65.4% and S. molesta biomass by 84.9% in an outdoor experiment. Another series of outdoor studies with both herbivore ecotypes on both plant species found that, in general, the smaller Florida ecotype impacted both Salvinia species more than did the larger Brazil ecotype. For example, feeding by the Florida ecotype reduced S. minima biomass by 78.1% and S. molesta by 89.8% while the Brazil ecotype reduced S. minima biomass by 43.7% and S. molesta by 52.5%. Herbivory also accelerated nutrient cycling, especially when plants were attacked by the Florida ecotype.
Technical Abstract: Ecotypes may arise following allopatric separation from source populations. The simultaneous transfer of an exotic plant to a novel environment, along with its stenophagous herbivore, may complicate more traditional patterns of divergence from the plant and insect source populations. We evaluated herbivory effects by two Cyrtobagous salviniae ecotypes on two species of Salvinia: the larger S. molesta and the smaller S. minima. Evaluations were based on biomass production, coverage, and nutrient dynamics in a series of laboratory and outdoor tank experiments. In general, the smaller Florida ecotype of C. salviniae impacted both Salvinia species more than the larger Brazil ecotype. In one experiment, herbivory by the Florida ecotype reduced S. minima biomass by 65.4% and S. molesta biomass by 84.9%. Other experiments produced similar results with ecotype effects on biomass, mean relative growth rate, plant cover, and the number of damaged buds. Herbivory, especially by the Florida ecotype, also accelerated nutrient cycling. The smaller size of the Florida ecotype may be adaptive by allowing maximal exploitation of host plants via internal larval feeding which presumably reduces predation risk while increasing damage to the plant. The overall asymmetry in plant responses to ecotype herbivory appears to be complementary and size dependent.