HORSE CHESTNUT SCALE (PULVINARIA-REGALIS) (HOMOPTERA, COCCIDAE) AND URBAN HOST TREE ENVIRONMENT

The analysis and explanation of the spatial distribution of organisms within a locality are problematic. This study uses a combination of st andard analytical methods (Generalized Linear Interactive Modeling [GL IM]) with recently developed spatial statistical techniques (geostatis tical analysis), on a model system of insect-plant interactions in an urban setting. Infestations of the horse chestnut scale, Pulvinaria re galis, were mapped on three tree species in Oxford, United Kingdom. Va rious tree parameters were measured, as were aspects of the site in wh ich each tree was growing. Using general linear modeling and geostatis tics, the distribution and intensity of scale populations were investi gated in relation to these parameters. The trees were separated into t hose that showed no symptoms of lack of vigor and those that were clea rly unhealthy. In both cases, the only parameter that explained much o f the variance in the scale egg densities on trees was the impermeabil ity of the substrate surface under the trees, such that as substrates became more impermeable to water and nutrients (for example, as a resu lt of concrete or roadways), the higher were the pest densities on tho se trees. For the vigorous trees alone, an extra parameter, that of bu ilding distance, was also found to be significant, so that trees very close to buildings also showed high pest densities. The spatial depend ence of scale insect eggs on trees was found to be anisotropic through the sample area, in the southwest/northeast direction, attributable t o wind speed, direction, and canyon effects.