TEMPORAL DISTRIBUTION OF PHYLLONORYCTER-ELMAELLA (LEPIDOPTERA, GRACILLARIIDAE) AND ITS MAJOR PARASITOID, PNIGALIO-FLAVIPES (HYMENOPTERA, EULOPHIDAE), IN WASHINGTON APPLE ORCHARDS

The seasonal occurrence of Phyllonorycter elmaella Doganlar & Mutuura, a tentiform leafminer, and its parasitoid, Pnigalio flavipes (Ashmead), in insecticide-free blocks located in commercial apple orchards was determined. P. Elmaella had three complete generations each year; population densities increased in each generation. P. Elmaella sap feeders (first to third instars) were "abnormally" abundant in the blocks at the end of each season, possibly because of a delay in their development. P. Flavipes had at least the same number of generations as P. Elmaella. Parasitoid activity decreased as the season progressed. Phenology data showed adult P. Flavipes emerged almost concurrently with adult P. Elmaella during the spring and summer generations, 2-3 wk before tissue feeders (fourth and fifth instars), were present in the orchard. This emergence pattern may be caused by a reproductive advantage for female P. Flavipes to feed on sap feeders before oviposition. The number of individuals of P. Elmaella that are able to overwinter successfully, rather than the seasonal levels of parasitism, seems to determine the leafminer's year-to-year population dynamics. However, parasitoid activity reduced the leafminer's intraseasonal population increase and kept its densities below treatment threshold levels in all orchard blocks examined. © 1990 Entomological Society of America.