Persistence and spread of Cryptococcus fagisuga, the initiating agent in beech bark disease (Fagus grandifolia).

摘要

Pathogens and parasites play important roles in ecological communities and their influence is meaningful when they represent a newly arrived invader. At geographic scales, invading tree pests have caused major disruptions of terrestrial ecosystems. The bark disease of American beech (Fagus grandifolia Ehrl.) is an example of a disease invasion that has had a major impact on forest composition throughout Northeastern, North America in the past 50 years. The combined infestation of the European beech scale insect Cryptococcus fagisuga Lind. and the subsequent invasion of fungi (Nectria spp.) have substantially altered the structure of American beech populations. Because the scale insect must precede the fungus, it is the key component of disease spread. Despite this, there is little ecological research in North America on the beech scale insect.; I examined the population and local dispersal dynamics of the beech scale insect on American beech populations in continuous forest inventory plots within the Edmund Niles Huyck Preserve in Eastern New York State. Fecundity and dispersal behavior were examined on the basis of insect population density on host trees. Weekly sampling was performed to determine fecundity and trap cards were used to determine percent wind dispersal. Outer bark cores were also taken to asses host resource quality. Range maps of the insect's dispersal were re-interpreted, using demographic patterns, to model the diffusive spread of the beech scale insect.; Results indicate that density of infestation has no measurable effect on scale fecundity or dispersal and that quality of host resources may play a large role in determining the level of scale insect infestation for the American beech. Growth rate, measured as the increase in density of scale colonies and transmission frequency, measured as probability of infection, indicate that there is little resistance to local dispersal. Geographic dispersal does fit a diffusion model, however estimated velocity was less than expected, and leads to a prediction of a two stage invasion sequence in the northern range of American beech, with slower expansion to the south.