Effect of within-field and landscape factors on insect damage in winter oilseed rape Johann G. Zaller * , Dietmar Moser, Thomas Drapela, Claudia Schmo ¨ger, Thomas Frank Department of Integrative Biology and Biodiversity Research, Institute of Zoology, University of Natural Resources and Applied Life Sciences Vienna, Gregor Mendel Strasse 33, A-1180 Vienna, Austria Received 30 January 2007; received in revised form 11 July 2007; accepted 16 July 2007 Available online 23 August 2007 Abstract It was investigated whether damage on winter oilseed rape (Brassica napus) caused by three major pests (rape and cabbage stem weevil, pollen beetle, brassica pod midge) was affected by within-field (soil quality, nitrogen fertilization level, plant development, stand density) and landscape factors (percentage B. napus area, isolation of B. napus fields, number of B. napus fields, average distance between study field and surrounding B. napus fields—all within a radius of 2000 m around the study fields). Damage and within-field/landscape relationships were analyzed on 29 landscape sectors using stepwise multiple regression analyses. Damage caused by stem weevil larvae was assessed by measuring the length of damaged stem pith on dissected B. napus stems, pollen beetle damage was assessed on top racemes by calculating the percentage of podless peduncles, damage by pod midge larvae was calculated as the percentage of yellow and prematurely split pods in the top racemes. Stem weevil and pollen beetle damage was significantly positively correlated with respective pest abundances, however no such relationship could be observed for pod midge. Oilseed rape yield was for all three damage measures significantly negatively related to the degree of damage. Multiple regression analyses revealed that pollen beetle and pod midge damage was negatively related to B. napus area in the surrounding landscape, while stem weevil damage showed a positive relationship with soil quality, plant development and stand density. The results indicated that pollen beetle and pod midge damage was mainly influenced by the amount of host plants in the landscape while stem weevil damage seemed to be more affected by within-field characteristics that might have altered the nutritional quality of the oilseed rape crop and/or the stand microclimate. # 2007 Elsevier B.V. All rights reserved. Keywords: Brassica napus; Ceutorhynchus napi; Ceutorhynchus pallidactylus; Dasineura brassicae; Herbivory; Meligethes aeneus; Winter oilseed rape 1. Introduction The importance of oilseed rape (Brassica napus L.) as a source for industrial and nutritional oil has been increasing worldwide and in some countries an increasing acreage is accompanied by a dramatic disproportionate increase of pesticide applications. For instance, in the USA, the harvested oilseed rape area increased fivefold from 1992 to 1997 (from 53,000 ha to 283,080 ha; FAOSTAT, http:// faostat.fao.org) while pesticide use in B. napus during this time increased more than 60-fold (from 2703 to 171,261 kg active ingredients year À1 ; Gianessi and Marcelli, 2000). For most of Europe, comparable data are lacking, however, data from the UK show a similar trend (50% increase in B. napus area versus 70% increased amount of insecticides applied; Garthwaite et al., 2004). In Europe the most important insect pests in B. napus are the cabbage stem flea beetle (Psylliodes chrysocephala L., Chrysomelidae), the pollen beetle (Meligethes aeneus F., Nitidulidae), the cabbage seed weevil (Ceutorhynchus assimilis Payk., Curculionidae), the rape stem weevil (C. napi Gyll.), the cabbage stem weevil (C. pallidactylus Marsh.) and the brassica pod midge (Dasineura brassicae Winn., Cecidomyiidae) (Alford et al., 2003). Although oilseed rape crop has been shown to compensate considerably after insect damage (Free and www.elsevier.com/locate/agee Agriculture, Ecosystems and Environment 123 (2008) 233–238 * Corresponding author. Tel.: +43 1 47654 3205; fax: +43 1 47654 3203. E-mail address: johann.zaller@boku.ac.at (J.G. Zaller). 0167-8809/$ – see front matter # 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.agee.2007.07.002