Comparative Densities of Beech Scale, Cryptococcus fagisuga, (Hemiptera: Eriococcidae) in the Country of Georgia and Massachusetts (USA), Parts of its Native and Invaded Ranges, on two Species of Beech

Authors

  • R. G. Van Driesche
  • G. Japoshvili

Abstract

The Caucasus Mountains in the country of Georgia are part of the native range of beech scale (Cryptococcus fagisuga) and Massachusetts (United States) is part of the invaded range of this species. As background to determine if the native range of this scale might be a source of natural enemies useful for correcting the ecological damage caused by beech scale in North America to America beech (Fagus grandifolia) comparative scale densities were measured in both locations in natural forest stands of F. grandifolia in Massachusetts and F. orientalis in Georgia. Average diameter at breast height (DBH) and health values were also compared. Scale densities were found to be 45.4-fold higher per unit area of bark in Massachusetts on F. grandifolia than in the country of Georgia on F. orientalis. Also, F. orientalis trees at sample sites in Georgia were 2.9-fold larger in DBH and much healthier that were F. grandifolia trees in Massachusetts. These data suggest that either F. orientalis is more resistant to beech bark disease than F. grandifolia or key natural enemies found in Georgia are missing in Massachusetts, or both. Cage exclusion studies are underway, separate from results reported here, to separate the effects of tree resistance and natural enemies.

Las montañas del Cáucaso en el país de Georgia son parte del área de distribución natural de la escama del haya (Cryptococcus fagisuga), y el estado del Massachusetts (Estados Unidos) es parte del rango geográfico invadido por esta especie. Para determinar si el área nativa de esta escama podría ser una fuente de enemigos naturales útiles para corregir el daño ecológico causado por esta especie a la haya americana (Fagus grandifolia), se midieron y compararon las densidades de la escama en áreas de bosques naturales de F. grandifolia en Massachusetts y F. orientalis en Georgia. También se comparó el promedio del diámetro a la altura del pecho DAP y la sanidad de los arboles. Se encontró que la densidad de escamas por unidad área fue 45.4 veces mayor en la corteza de F. grandifolia en Massachusetts que en la corteza de F. orientalis en Georgia. Además, los árboles muestreados en Georgia (F. orientalis) fueron 2.9 veces más grandes en términos de DAP y mucho más sanos que F. grandifolia en Massachusetts. Estos datos sugieren que F. orientalis es más resistente a la enfermedad de la corteza del haya que F. grandifolia, que los principales enemigos naturales que se encuentran en Georgia no están presentes en Massachusetts, o ambas cosas. Otros estudios utilizando técnicas de exclusión con jaulas están en marcha para separar los efectos de la resistencia de los árboles de los efectos causados por los enemigos naturales.

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Published

2012-06-01

Issue

Vol. 95, No. 2 (June 2012)

Section

Research Papers

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