ECOLOGY AND POPULATION BIOLOGY Allothrombium mitchelli (Acari: Trombidiidae) in the Great Smoky Mountains National Park: Incidence, Seasonality, and Predation on Beech Scale (Homoptera: Eriococcidae)

American beech gaps in the southern Appalachian mountains are currently threatened by an insect-mediated disease complex known as beech bark disease. Cryptococcus fagisuga Lindinger, or beech scale, a major component of beech bark disease, wounds trees through feeding on vascular tissue through the outer cambium. This feeding method leaves numerous wounds and provides entryways for infection by fungal pathogens. Allothrombium mitchelli Davis, a large red velvet mite, was found in the Great Smoky Mountains National Park, where it was observed to feed onbeech scale. First-instar larvae ofA.mitchelli are quiescent, and deutonymphs are the onlymobile immature stage.A.mitchelli probably has one generation per yearwith adult population peaks in late spring and early fall; deutonymph populations also peaked in early fall within the areas studied. Both adults and deutonymphs feed onbeech scale. In 1996,miteswere found on 22.1%of beech trees (n 453) in selectedplots; incidencewas greatest at SweatHeifer on 9May (81%,n 29).Mite incidence was signiÞcantly inßuenced by categorized aspect ( 2 57.92, P 0.0001, n 453) and categorized elevation ( 2 101.33, P 0.0001, n 453). A strong signiÞcant (0.4528, P 0.0001) correlation was observed between mite incidence and elevation. A weak but signiÞcant negative correlation (-0.1341, P 0.0001)was found between numbers ofA. mitchelli on individual trees and beech scale ratings at Sweat Heifer and Indian Gap plots. Although their status as a biological control agent of beech scale is uncertain, A. mitchelli is one of only a few species that has been observed to feed consistently on beech scale.