Mapping dispersal of an invasive gallmaker using GIS and remote sensing: Localized proliferation of the Asian chestnut gall wasp

Remote sensing and spatial analysis represent useful tools for modeling species’ dispersal, thus allowing more accurate predictions for developing mitagation strategies. American chestnut, Castanea dentata, was historically a dominant forest species in North America, but occurs only sporadically today after its functional elimination by an exotic fungal pathogen in the early 1900’s. In recent decades Castanea resources have increased due to restoration efforts and horticultural uses. An additional exotic, the globally invasive Asian chestnut gall wasp Dryocosmus kuriphilus is threatening chestnut cultivation. We use remotely sensed data and Geographic Information Systems to describe host distribution and the occurrence of the gall wasp in Lexington, Kentucky. We test the hypotheses that geomorphology, host occurrence, and prevaling winds influence local proliferation. We located 27 chestnuts within a 40 km² study area, situated on high elevations and low slopes. In 2010 the gall wasp was found on only one tree, facing southwest. In 2011 17 additional trees were reported to be infested, primarly located 700 – 2700 m south southwest of the source tree. During adult flight (June 23 – July 4 2010), prevailing winds on 4 days were south westerly, thus accounting for the pattern of gall wasp infested trees evident in 2011. Our data support the hypothesis that gall wasp spread is attributable to prevailing winds occurring during adult insect emergence, and influenced by topography, thus suggesting that weather data and topographic features can be used to delineate currently infested areas and predict future infestations.