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Fordingbridge, United Kingdom

Winder L.,Unitec Institute of Technology | Alexander C.J.,James Hutton Institute | Woolley C.,University of Witwatersrand | Perry J.N.,Rothamsted Research | Holland J.M.,Farmland Ecology Unit

An understanding of spatial and temporal processes in agricultural ecosystems provides a basis for rational decision-making with regards to the management and husbandry of crops, supporting the implementation of integrated farming strategies. In this study we investigated the spatial and temporal distribution of aphid pests (Sitobion avenae and Metopolophium dirhodum) within winter wheat fields. Using an intensive sampling programme we investigated distributions at both the small (single shoot) and large (field) scales. Within two fields, a grid with 82 locations was established (area 120 m by 168 m). At each location, 25 shoots were individually marked and aphid counts by observation conducted on 21 and 22 occasions as the crop matured, resulting in 43,050 and 45,100 counts being conducted in the two fields respectively. We quantified field scale spatial distributions, demonstrating that spatial pattern generally emerged, with temporal stability being both species- and field- dependent. We then measured turnover of colonies at the small (individual shoot) and large (field) scales by comparing consecutive pairs of sampling occasions. Four turnover categories were defined: Empty (no aphids recorded on either occasion); Colonised (aphids recorded on the second occasion but not the first); Extinction (aphids recorded on the first occasion but not the second); Stable (aphids recorded on both occasions). At the field scale, population stability soon established, but, at the small scale there was a consistently high proportion of unoccupied shoots with considerable colonisation and extinction and low stability. The redistribution of aphids within the crop at the local scale is a vulnerability which could be used to disrupt population development - by mediating exposure to ground-active natural enemies and by incurring a metabolic cost caused by the physiological demands to re-establish on a nearby host plant. © 2014 Winder et al. Source

Winder L.,Unitec Institute of Technology | Alexander C.J.,James Hutton Institute | Woolley C.,41 Green End | Perry J.N.,Rothamsted Research | Holland J.M.,Farmland Ecology Unit
Arthropod-Plant Interactions

We investigated, within two cereal fields in Southern England, the within-canopy spatial distribution of the aphids Sitobion avenae and Metopolophium dirhodum in relation to crop yield and plant nitrogen. We extended the study to investigate the spatial distribution of aphids that fell to, or returned from, the ground in order to estimate availability of the within-canopy aphid population to ground-active predators. We revealed that crop canopy aphid spatial pattern was associated with nitrogen or yield. Differences were evident between species: S. avenae was generally negatively associated with yield or plant nitrogen, whilst M. dirhodum exhibited positive association. For both aphid species, we observed strong spatial pattern for aphids falling to the ground and conclude that this could, in part, mediate the effectiveness of ground-active predators as pest control agents. © The Author(s) 2012. Source

Holland J.M.,Farmland Ecology Unit | Oaten H.,Farmland Ecology Unit | Moreby S.,Farmland Ecology Unit | Birkett T.,Farmland Ecology Unit | And 3 more authors.
Agriculture, Ecosystems and Environment

The impact of two predatory guilds, epigeal and aerial natural enemies, on levels of cereal aphid control in winter wheat was examined on farms with contrasting proportions of grass margins, one of the most popular agri-environment options in England. In year 1, by 14. d after inoculation the aerial natural enemies alone had caused substantial reductions (88%) in numbers of cereal aphids compared to where no natural enemies were present. In contrast, epigeal predators achieved a 31% reduction, although this reached 88% after 28. d. In year 2, both aerial and epigeal natural enemies achieved over 87% control after 14. d. Aerial natural enemies were largely comprised of predatory Diptera and Linyphiidae (Araneae). Levels of control were positively related to the proportion of linear grass margins within 250, 500 and 750. m radii of the study arenas. There was weaker evidence that hedgerows decreased aphid control by epigeal predators. This study demonstrated that an agri-environment option can be used to improve an ecosystem service on arable farmland. © 2012 Elsevier B.V. Source

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