AbstractThe relationship between yellow sticky trap catches of Pholetesor (= Apanteles) ornigis (Weed) and its emergence during the first two of its three yearly emergence periods was examined using four trap locations in five commercial apple orchards in Norfolk County, Ont., during 1984 and 1985. Orchards were divided into two zones: the border row of trees (= peripheral zone) and all trees within the border row (= interior zone). Traps were positioned within and below the tree canopy in the two zones.The sensitivity of the yellow traps to first male and female spring emergence was similar. Trap location had no obvious effect on the relationship between first spring emergence and first spring trap catch of males and females. The traps were similar in sensitivity to peak male and female spring emergence. Trap location affected the relationship between peak male emergence and peak male trap catch during the spring emergence period; the number of parasites caught on traps placed below the tree in the interior zone was the best indicator of peak male emergence. Trap location did not affect the relationship between peak female emergence and peak female trap catch during the spring emergence period.The yellow traps were more sensitive to male than to female first emergence during the first summer emergence period. During this emergence period, trap location had no obvious effect on the relationship between first emergence and first trap catch of males and females. The traps were more sensitive to peak male than to peak female emergence during the first summer emergence period. The number of male parasites caught on traps placed within the tree in the peripheral zone gave the best indication of peak male emergence during the first summer emergence period. The most accurate indication of peak female emergence was given by the number of female parasites caught on traps placed within or below the tree in the interior zone of the orchard.During the spring emergence period, few parasites were caught after emergence was complete, whereas during the first summer emergence period, relatively large numbers of parasites were sometimes caught up to 2 weeks after emergence was complete.The application of the results for monitoring P. ornigis emergence is discussed.