Comparative phenology and cohort survival of beech scale (Hemiptera: Eriococcidae) in part of its native range (Caucasus Mountains, Georgia) and in an invaded area (Massachusetts, USA)
Keywords:
overwintering stage, natural enemy exclusion, beech forest, invasive insectAbstract
The phenology and survival of beech scale, Cryptococcus fagisuga Lindinger (Hemiptera: Eriococcidae), were investigated in part of its native range (Caucasus Mountains, Georgia) and in an invaded area (Massachusetts, USA). Despite nearly identical growing seasons (as measured by cumulative day-degrees), the scale was found to be bivoltine in the Caucasus Mountain region but univoltine in Massachusetts. In Georgia, scales overwintered as adults, whereas in Massachusetts, 1st instar crawlers were the overwintering stage. In Massachusetts, protective cages increased scale survival over a year-long period, but the effect was not great and was presumed to be due to exclusion of generalist predators, not specialized natural enemies. There was no effect of caging on survival in Georgia, and no support was found for the hypothesis that specialized natural enemies might exist in the scale’s native range that might be imported for biological control of the pest in the United States. Rather, it appears that selection for resistance in American beech (Fagus grandifolia Ehrhart; Fagales: Fagaceae) may offer the best chance to restore healthy stands of American beech in North American forests.
Resumen
Se investigó la fenología y sobrevivencia de la escama de la haya, Cryptococcus fagisuga Lindinger (Hemiptera: Eriococcidae), en parte en su área de distribución natural (Cáucaso Mts., en el pais de Georgia.) y en una zona invadida (Massachusetts, EE.UU.). Se encontró que la escama es bivoltina en la región de las Montañas del Cáucaso, pero univoltina en Massachusetts, a pesar de las estaciones de crecimiento casi idénticas (medido por grados días acumulados). En Georgia, la escama como adulto inverna, mientras que en Massachusetts, inverna en el estadio del primer instar (rastreadores). En Massachusetts, las jaulas protectoras aumentó la sobrevivencia de la escama durante un período de un año, pero el efecto no fue grande y se atribuyó a depredadores generalistas, no enemigos naturales especializados. No hubo efecto de las jaulas sobre la sobrevivencia en Georgia y no se encontró apoyo para la hipótesis de que podrían existir enemigos naturales especializdos en el área de distribución natural de la escama que podrían ser importados para el control biológico de la plaga en los Estados Unidos. Más bien se recomienda que la selección para la resistencia en las líneas de haya americana (Fagus grandifolia Ehrhart; Fagales: Fagaceae) ofrece la mejor oportunidad para restaurar la salud de los rodales de haya americana en los bosques de América del Norte.
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