RELATION OF SEXUPARA PRODUCTION IN THE WOOLLY PEAR APHID, ERIOSOMA PYRICOLA (HOMOPTERA: PEMPHIGIDAE), TO TREE GROWTH IN THE FIELD

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Abstract
Sexupara production in the pear root aphid, Eriosoma pyricola Baker & Davidson, was closely associated with the cessation of shoot growth of its host in the field in irrigated and non-irrigated plots in two successive, but phenologically different years. Neither the environment nor the host plant were unfavorable at the time the sexuparae were formed, indicating that the aphid uses the host plant as a source of seasonal information. The nature of synchronization between active development of univoltine insects and trees is discussed. It is concluded that the initiation of dormancy in trees and diapause in insects is not likely to be synchronized by a common set of environmental factors. Either regulation of insect diapause by host trees is more common than is currently recognized, or environmental and age differences in tree growth have favored selection for obligate diapause.