Spatial characteristics and effects of fall density and weather on overwintering loss of pear psylla (Homoptera: Psyllidae). Horton, D. R, Higbee, B. S, Unruh, T. R, & Westigardi, P. H Environmental Entomology, 21(6):1319–1332, 1992.
Spatial characteristics and effects of fall density and weather on overwintering loss of pear psylla (Homoptera: Psyllidae) [link]Paper  doi  abstract   bibtex   
Overwintering loss of pear psylla, Cacopsylla pyricola Foerster, in the Yakima area of Washington and the Medford area of Oregon, was estimated as the difference between the peak beat tray count obtained in fall and the peak count obtained the following spring. Thirty five orchards were sampled over 13 yr at Yakima, and 12 orchards were sampled for 10 yr at Medford. Overwintering loss increased linearly with peak fall counts. Loss coefficients were ≥0.90 in three of four regions at Yakima and in all 12 orchards at Medford. Peak spring counts were independent of peak fall counts in three of four regions at Yakima and at 6 of 12 orchards at Medford. At Yakima, peak spring count was positively correlated with November precipitation and negatively correlated with November and January temperature; overwintering loss increased with increasing January temperahue and decreased with increasing November precipitation. At Medford, overwintering loss increased with decreasing fall precipitation but, in contrast to Yakima, increased also with decreasing January temperatures. We suggest that wet auhunns result in higher overwintering success by causing a reduction in dispersal from pear. Spatial autocorrelation showed that peak counts were more similar among neighboring orchards than between distantly separated orchards for two of six analyses in spring and one of six analyses in fall. Counts were less variable in spring than in fall, consistent with the hypothesis that psylla reallocate among orchards between fall and spring. The claim that orchards with intensive pesticide use in some regions have higher fall counts than less intensively managed orchards was tested for Yakima; no differences in counts were noted in commercial versus organic orchards. Initial pesticide applications in spring at a chemically intensive orchard preceded peak spring counts in a neighboring unsprayed orchard by 4–5 d, resulting in an estimated seasonal peak count that was about four psylla per tray lower than what would occur in the absence of pesticides. Julian day of peak spring counts occurred earlier in the wanner regions of the Yakima valley. Variation between regions in timing of spring peaks was eliminated by expressing timing in degree-days (DD); for the Yakima valley, peak counts occurred at ≍80 DD using a lower threshold of 5°C.
@article{horton_spatial_1992,
	title = {Spatial characteristics and effects of fall density and weather on overwintering loss of pear psylla ({Homoptera}: {Psyllidae})},
	volume = {21},
	issn = {1938-2936},
	url = {https://academic.oup.com/ee/article-abstract/21/6/1319/2394405},
	doi = {10.1093/ee/21.6.1319},
	abstract = {Overwintering loss of pear psylla, Cacopsylla pyricola Foerster, in the Yakima area of Washington and the Medford area of Oregon, was estimated as the difference between the peak beat tray count obtained in fall and the peak count obtained the following spring. Thirty five orchards were sampled over 13 yr at Yakima, and 12 orchards were sampled for 10 yr at Medford. Overwintering loss increased linearly with peak fall counts. Loss coefficients were ≥0.90 in three of four regions at Yakima and in all 12 orchards at Medford. Peak spring counts were independent of peak fall counts in three of four regions at Yakima and at 6 of 12 orchards at Medford. At Yakima, peak spring count was positively correlated with November precipitation and negatively correlated with November and January temperature; overwintering loss increased with increasing January temperahue and decreased with increasing November precipitation. At Medford, overwintering loss increased with decreasing fall precipitation but, in contrast to Yakima, increased also with decreasing January temperatures. We suggest that wet auhunns result in higher overwintering success by causing a reduction in dispersal from pear. Spatial autocorrelation showed that peak counts were more similar among neighboring orchards than between distantly separated orchards for two of six analyses in spring and one of six analyses in fall. Counts were less variable in spring than in fall, consistent with the hypothesis that psylla reallocate among orchards between fall and spring. The claim that orchards with intensive pesticide use in some regions have higher fall counts than less intensively managed orchards was tested for Yakima; no differences in counts were noted in commercial versus organic orchards. Initial pesticide applications in spring at a chemically intensive orchard preceded peak spring counts in a neighboring unsprayed orchard by 4–5 d, resulting in an estimated seasonal peak count that was about four psylla per tray lower than what would occur in the absence of pesticides. Julian day of peak spring counts occurred earlier in the wanner regions of the Yakima valley. Variation between regions in timing of spring peaks was eliminated by expressing timing in degree-days (DD); for the Yakima valley, peak counts occurred at ≍80 DD using a lower threshold of 5°C.},
	number = {6},
	journal = {Environmental Entomology},
	author = {Horton, David R and Higbee, Bradley S and Unruh, Thomas R and Westigardi, Peter H},
	year = {1992},
	pages = {1319--1332}
}
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