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Effects of organic and conventional fertilizer treatments on host selection by the aphid parasitoid Diaeretiella rapae

Pope, T.W.; Girling, R.D.; Staley, J.T.; Trigodet, B.; Wright, D.J.; Leather, S.R.; van Emden, H.F.; Poppy, G.M.. 2012 Effects of organic and conventional fertilizer treatments on host selection by the aphid parasitoid Diaeretiella rapae. Journal of Applied Entomology, 136 (6). 445-455. 10.1111/j.1439-0418.2011.01667.x

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Abstract/Summary

The type and quantity of fertilizer supplied to a crop will differ between organic and conventional farming practices. Altering the type of fertilizer a plant is provided with can influence a plant’s foliar nitrogen levels, as well as the composition and concentration of defence compounds, such as glucosinolates. Many natural enemies of insect herbivores can respond to headspace volatiles emitted by the herbivores’ host plant in response to herbivory. We propose that manipulating fertilizer type may also influence the headspace volatile profiles of plants, and as a result, the tritrophic interactions that occur between plants, their insect pests and those pests’ natural enemies. Here, we investigate a tritrophic system consisting of cabbage plants, Brassica oleracea, a parasitoid, Diaeretiella rapae, and one of its hosts, the specialist cabbage aphid Brevicoryne brassicae. Brassica oleracea plants were provided with either no additional fertilization or one of three types of fertilizer: Nitram (ammonium nitrate), John Innes base or organic chicken manure. We investigated whether these changes would alter the rate of parasitism of aphids on those plants and whether any differences in parasitism could be explained by differences in attractivity of the plants to D. rapae or attack rate of aphids by D. rapae. In free-choice experiments, there were significant differences in the percentage of B. brassicae parasitized by D. rapae between B. oleracea plants grown in different fertilizer treatments. In a series of dual-choice Y-tube olfactometry experiments, D. rapae females discriminated between B. brassicae-infested and undamaged plants, but parasitoids did not discriminate between similarly infested plants grown in different fertilizer treatments. Correspondingly, in attack rate experiments, there were no differences in the rate that D. rapae attacked B. brassicae on B. oleracea plants grown in different fertilizer treatments. These findings are of direct relevance to sustainable and conventional farming practices.

Item Type: Publication - Article
Digital Object Identifier (DOI): 10.1111/j.1439-0418.2011.01667.x
Programmes: CEH Topics & Objectives 2009 onwards > Biodiversity > BD Topic 3 - Managing Biodiversity and Ecosystem Services in a Changing Environment > BD - 3.1 - Develop methods to quantify the link between biodiversity ..
CEH Sections: Pywell
ISSN: 0931-2048
Additional Keywords: attack rate, braconid, Brevicoryne brassicae, cabbage aphid, olfactometer, parasitism
NORA Subject Terms: Agriculture and Soil Science
Ecology and Environment
Date made live: 27 Jan 2012 16:48
URI: http://nora.nerc.ac.uk/id/eprint/16536

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