title: Nonrandom Distribution of Cabbage Aphids (Hemiptera: Aphididae) in Dryland Canola (Brassicales: Brassicaceae).
abstract: Characterization of spatial distribution patterns of pests in large-scale agricultural fields is important because these patterns affect the sampling effort needed to accurately detect and estimate their population density. In this study, we conducted experimental releases of alate cabbage aphids (Brevicoryne brassicae L.) into centers of small plots of canola (Brassica napus L.), and their gradual spread over a 7-wk period was characterized. The small-plot experiment demonstrated gradient effects from plot centers and a nonrandom vertical distribution, with initial colonization occurring on the abaxial side of lower canopy leaves and, later, highest numbers of cabbage aphids occurring on racemes. We also conducted large-scale distribution analyses of cabbage aphid infestations in two commercial canola fields, using visual inspection and sweep net sampling. We used canola plant phenological and landscape features as explanatory variables of the spatial distribution of cabbage aphid counts. These large-scale experiments showed strong edge effects with negative associations between cabbage aphid counts and distance to crop edges, including tree lines and contour banks. Cabbage aphid distribution was more effectively displayed using logistic regression than ordinary regression, Spatial Analysis by Distance IndicEs, or both. Based on the study findings, a nonrandom or optimized inspection approach is proposed to focus monitoring efforts on canola plants within 20 m from field edges with particular attention to the abaxial side of lower-canopy leaves. Detection of advanced cabbage aphid infestations should target the racemes within 20 m from field edges.
authors: The University of Western Australia, School of Animal Biology, The UWA Institute of Agriculture, 35 Stirling Highway, Crawley, Perth, Western Australia 6009, Australia. Department of Agriculture and Food Western Australia, 3 Baron-Hay Court, South Perth, Western Australia 6151, Australia. dustin.severtson@research.uwa.edu.au.
authors: Dustin
authors: D
authors: Severtson
authors: The University of Western Australia, School of Plant Biology, The UWA Institute of Agriculture, 35 Stirling Highway, Crawley, Perth, Western Australia 6009, Australia.
authors: Ken
authors: K
authors: Flower
authors: The University of Western Australia, School of Animal Biology, The UWA Institute of Agriculture, 35 Stirling Highway, Crawley, Perth, Western Australia 6009, Australia. Department of Entomology and Nematology, UC Davis Briggs Hall, Davis, CA.
authors: Christian
authors: C
authors: Nansen
mesh_terms: D063147:Animal Distribution; D000818:Animals; D001042:Aphids / Q000502:physiology*; D029688:Brassica napus / Q000254:growth & development; D020387:Food Chain; D060434:Herbivory; D011156:Population Density; D013997:Time Factors; D014904:Western Australia
keywords: edge effect; integrated pest management; spatial distribution; targeted sampling