Questions consistently arise as to the status of Agrilus planipennis populations and the persistence of ash in forested settings, particularly in the original core of the A. planipennis infestation in southeast Michigan. I sampled A. planipennis populations in 24 green ash (Fraxinus pennsylvanica) sites, each 1 ha in size. Eight sites were located in each of three areas of southern Michigan representing (1) the original A. planipennis Core; (2) the invasion Crest, in south central Michigan, where A. planipennis populations were currently peaking, and (3) the invasion Cusp, in southwest Michigan where A. planipennis had recently become established. Adult A. planipennis were captured in all 24 sites in both years of the study. No larvae were present in the two most westerly Cusp sites in 2010, but larvae were present in all 24 sites in 2011. Despite the depletion of overstory ash in southeast Michigan, A. planipennis continues to infest and kill trees in Core sites. Beetle populations were highest in south central Michigan and are rising in southwestern Michigan. Mortality of overstory ash decreased across an east to west gradient across southern Michigan. Green ash was abundant in the understory of all sites including Core sites. There was no evidence of current year ash germination in Core sites in southeast Michigan. If A. planipennis persists in these areas, regenerating ash will continue to become infested and killed, and potentially eliminating ash from these systems.
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