Submitted to: Journal of British Columbia Entomological Society
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/10/2007
Publication Date: 12/15/2007
Citation: Cockfield, S.D., Beers, E.H., Horton, D.R., Miliczky, E. 2007. Timing of oviposition of thrips (thysanoptera: thripidae) in apple fruit. Journal of British Columbia Entomological Society 104:45-53.
Interpretive Summary: Egglaying by western flower thrips causes damage to apple fruit (“pansy spot”), but it is not yet clear at what stage of apple development that the damage occurs. Scientists with Washington State University, Wenatchee, WA and USDA-ARS, Yakima Agricultural Research Laboratory, Wapato, WA examined fruit collected at different growth stages and conducted insecticide trials to determine when thrips began depositing eggs into apple fruit. Studies showed that much of the pre-bloom and full bloom egg laying occurred in non-damaging areas of the apple blossom, and that eggs deposited after petal fall were damaging; the results were confirmed with insecticide trials. Our data indicate that recommendations in current pest control guides should be modified, as the information in those guides would lead to spray applications being made too early in the growing season.
Technical Abstract: Adult thrips were most abundant on flower clusters of apple, Malus × domestica Borkhausen, from king bloom to full bloom. Low numbers of thrips remained on the clusters after petal fall as fruit enlarged. Immature thrips peaked in numbers after densities of adults had peaked, usually by petal fall. Two staining procedures were developed for detecting oviposition in fruit, and in non-damaging areas within blossom clusters including leaves, stem tissues, and flower calyx. Eggs were abundant in non-damaging areas throughout the bloom and post-bloom periods; the calyx appeared to be highly preferred. Few eggs were detected in fruit during bloom. Egg numbers in fruit began to increase about 8-13 d after full bloom, when fruit had grown beyond 5 mm diameter. The most effective timing of pesticides corroborated the oviposition data. Formetanate hydrochloride or spinosad caused the greatest reduction in oviposition injury (pansy spot) when applied from full bloom to about 5 mm fruit diameter.