Toward management guidelines for soybean aphid, Aphis glycines, in Quebec. II. Spatial distribution of aphid populations in commercial soybean fields

Abstract

AbstractThe study was conducted to document the spatial distribution of the soybean aphid, Aphis glycines Matsumura (Hemiptera: Aphididae), in commercial fields of soybean, Glycine max (L.) Merr. The abundance of aphids was assessed weekly at 12 sites in 2005 and 2006 on more than 135 georeferenced plants per site. Variograms and principal coordinates of neighbour matrices (PCNM) were used to detect significant spatial structures. Variograms indicated a spatially random distribution of aphid populations in a majority (84%) of fields-weeks. For the variograms with a defined structure, the variance between pairs of observations generally increased rapidly with the distance between plants up to a distance where it stabilized, a pattern adequately fitted by spherical models. Structured spatial distributions were more prevalent in 2005 than in 2006, especially at the end of the season. In 2006, PCNM analysis was more sensitive in detecting spatial trends than were variograms. PCNM analysis revealed significant patterns across a broad range of scales, with dominant periods averaging 22.6 and 47.1 m for the short and long transects, respectively. Sampling plants along a 100 m long transect at about 7.5 m intervals in soybean fields would allow detection of the spatial structures identified in this study.