Submitted to: Journal of British Columbia Entomological Society
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/24/2007
Publication Date: 12/20/2007
Citation: Miliczky, E., Cockfield, S.D., Beers, E.H., Horton, D.R. 2007. Spatial patterns of western flower thrips in apple orchards and associated fruit damage. Journal of British Columbia Entomological Society 104:25-33.
Interpretive Summary: Western flower thrips may often cause extensive damage to green-skinned cultivars of apples, but the relationship between sampling location and thrips densities in apple orchards is poorly known. ARS scientists at the Yakima Agricultural Research laboratory in collaboration with scientists at Washington State University showed that thrips densities and frequency of fruit damage declined with increasing distance into the orchard. The studies are the first to demonstrate quantitatively the relationship between sampling location and thrips density or damage in apples. Results will assist growers and pest control consultants as they sample flower thrips in apple orchards.
Technical Abstract: Western flower thrips, Frankliniella occidentalis (Pergande), is a pest of apples in orchards of North America. Flower thrips causes damage (“pansy spot”) to apples by its egglaying activities during the bloom and post-bloom periods. Difficulties in monitoring this pest have complicated control efforts in apple orchards. Densities of western flower thrips were monitored in 7 (2003) or 8 (2004) apple orchards at each of 4 bloom stages; in each orchard, thrips counts in blossom clusters were estimated at 4 to 6 distances into the orchard from an orchard edge that abutted native range habitat. We hypothesized that numbers of thrips in blossoms would decline with increasing distance along transects into orchards if the native habitat acted as a source of thrips. Numbers in blossom clusters peaked at full bloom and petal fall. Densities showed a linear drop with increasing distance into the orchard, which we interpreted as evidence that the native habitat adjacent to each orchard did indeed act as a source of thrips moving into the orchards. Pansy spot declined in incidence with increasing distance into the orchard. The major drop in damage occurred between the border row trees and samples taken at the adjacent distance (9 m), suggesting that border rows adjacent to native habitats should be monitored with particular care. Regression analyses showed that damage and thrips density were positively correlated, albeit with substantial levels of unexplained variation in levels of damage.