The biology of Rosa multiflora (Rosaceae) and two of its biotic mortality factors
Rosa multiflora Thunb. (Rosaceae), an invasive plant in the eastern U.S., was planted in the 1940's as a living fence, for wildlife cover and to prevent soil erosion. However, R. multiflora rapidly spread from these original plantings via seeds and clonally, invading pasture and wooded areas. We found that at the scale of contiguous plants (patches) R. multiflora is spreading clonally and through sexual reproduction. Although there were multiple genotypes in the large patches of R. multifora, overall genetic diversity was consistent with clonal reproduction;Invasive species often require mutualistic relationships to successfully invade new environments. Insect pollination is an example of a mutualism that is required for seed set in the invasive species, Rosa multiflora Thunb. (Rosaceae), an obligate outcrosser. We determined that the insect pollinators visiting R. multiflora flowers in Iowa were Syrphidae, Bombus sp. and Apis mellifera. Our results indicate that R. multiflora is utilizing common generalist insect pollinators in Iowa and pollination is not a limiting factor for this invasive species;A disease of unknown etiology, rose rosette disease (RRD), infects R. multiflora and other Rosa species and is believed to be transmitted by Phyllocoptes fructiphilus Keifer (Acari: Eriophyidae). We found that Phyllocoptes fructiphilus was present on healthy R. multiflora growing in the open and as an under-story plant, but the greatest numbers were observed on plants RRD growing in the sun. Several other mite species, aphids, and thrips species occur in the same plant microhabitat as P. fructiphilus. Future research needs to isolate and identify the causal agent of RRD so it can be confirmed that only P. fructiphilus vectors RRD;The larvae of Megastigmus aculeatus var nigroflavus Hoffmeyer (Hymenoptera: Torymidae), feed on the developing R. multiflora seeds and may have the potential to reduce seed output. We found M. aculeatus larvae at 31 of the 49 sites sampled in Iowa. We observed a significant reduction in both viable and aborted seeds in hips attacked by M. aculeatus. Detailed knowledge of R. multiflora demography is necessary to determine at what level seed predation will reduce the recruitment of new individuals into the population.