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Semi-natural habitats in agricultural landscapes may support parasitoid populations that provide biocontrol services by suppressing populations of crop pests, but little is known about the spatial pattern and variability of these services at different levels of scale. Here we investigate the rarely studied phenomenon of early-season crop colonization by parasitoids and the relationship with the surrounding landscape. We assessed parasitism of whiteflies by placing whitefly infested cotton seedlings in remnant vegetation, arable land 25–125 m from remnant vegetation, and arable land further than 400 m from remnant vegetation. Twelve to twenty sentinel plants were exposed in a 25 × 25 m grid pattern in plots in each habitat. The experiment was conducted at 18 locations across two landscapes and repeated three times in a 2-week period in 2007 and 2008. Parasitism was observed during the first three days after the introduction of the whitefly infested seedlings and was in all cases caused by Encarsia spp. The mean number of parasitized whitefly per plant was 0.106 ± 0.025 and was highest on cotton plants placed in remnant vegetation, declining with increasing distance from remnant vegetation. A regression model with land use and meteorological variables received more statistical support from the data than models with only landscape and time period as factors. Parasitism levels were influenced by the proportion of remnant vegetation, grassland, as well as wind, temperature, dew point temperature and year. Early-season colonization of whitefly infested seedlings by parasitoids was erratic and characterized by large spatial (inter-plant and inter-plot) and temporal variation. Our study confirms that remnant vegetation function as reservoirs for parasitoids and that parasitoids can penetrate arable fields beyond 125 m within 3 days. However, variation in the occurrence of parasitism makes it difficult to predict parasitoid colonization at a specific place and time. Therefor

Background: Phloem-feeding insects are among the most devastating pests worldwide. They not only cause damage by feeding from the phloem, thereby depleting the plant from photo-assimilates, but also by vectoring viruses. Until now, the main way to prevent such problems is the frequent use of insecticides. Applying resistant varieties would be a more environmental friendly and sustainable solution. For this, resistant sources need to be identified first. Up to now there were no methods suitable for high throughput phenotyping of plant germplasm to identify sources of resistance towards phloem-feeding insects. Results: In this paper we present a high throughput screening system to identify plants with an increased resistance against aphids. Its versatility is demonstrated using an Arabidopsis thaliana activation tag mutant line collection. This system consists of the green peach aphid Myzus persicae (Sulzer) and the circulative virus Turnip yellows virus (TuYV). In an initial screening, with one plant representing one mutant line, 13 virus-free mutant lines were identified by ELISA. Using seeds produced from these lines, the putative candidates were re-evaluated and characterized, resulting in nine lines with increased resistance towards the aphid. Conclusions: This M. persicae-TuYV screening system is an efficient, reliable and quick procedure to identify among thousands of mutated lines those resistant to aphids. In our study, nine mutant lines with increased resistance against the aphid were selected among 5160 mutant lines in just 5 months by one person. The system can be extended to other phloem-feeding insects and circulative viruses to identify insect resistant sources from several collections, including for example genebanks and artificially prepared mutant collections.