Diagnostic PCR assays to unravel food web interactions in cereal crops with focus on biological control of aphids

Karin Staudacher,Mattias Jonsson,Michael Traugott

doi:10.1007/s10340-015-0685-8

Abstract

Successful biological control of agricultural pests is dependent on a thorough understanding of the underlying trophic interactions between predators and prey. Studying trophic interactions can be challenging, particularly when generalist predators that frequently use multiple prey and interact with both pest and alternative prey are considered. In this context, diagnostic PCR proved to be a suitable approach, however at present, prey-specific PCR primers necessary for assessing such interactions across trophic levels are missing. Here we present a new set of 45 primers designed to target a wide range of invertebrate taxa common to temperate cereal crops: cereal aphids, their natural enemies such as carabid beetles, ladybeetles, lacewings, and spiders, and potential alternative prey groups (earthworms, springtails, and dipterans). These primers were combined in three ‘ready to use’ multiplex PCR assays for quick and cost-effective analyses of large numbers of predator samples. The assays were tested on 560 carabids collected in barley fields in Sweden. Results from this screening suggest that aphids constitute a major food source for carabids in cereal crops (overall DNA detection rate: 51 %), whereas alternative extraguild and intraguild prey appear to be less frequently preyed upon when aphids are present (11 % for springtails and 12 % for earthworms; 1 % for spiders and 4 % for carabids). In summary, the newly developed molecular assays proved reliable and effective in assessing previously cryptic predator–prey trophic interactions, specifically with focus on biological control of aphids. The diagnostic PCR assays will be applicable manifold as the targeted invertebrates are common to many agricultural systems of the temperate region.Electronic supplementary materialThe online version of this article (doi:10.1007/s10340-015-0685-8) contains supplementary material, which is available to authorized users.

Highlights

Biological control of agricultural pests by natural enemies is an ecosystem service of immense economic value (Landis et al 2008; Losey and Vaughan 2006; Ostman et al 2003)
Two alternative primer pairs each were developed for aphids, springtails, dipterans, Pachygnatha spp., Harpalus spp., and Coccinella septempunctata to have both a longer and shorter amplicon providing more flexibility for combining the primer pairs in customised multiplex PCR assays (Fig. 1; Tables 1, 3)
With the specific purpose of making the presented molecular detection system available as a ‘ready to use’ approach, these primers have been combined into three multiplex PCR assays

Summary

Introduction

Biological control of agricultural pests by natural enemies is an ecosystem service of immense economic value (Landis et al 2008; Losey and Vaughan 2006; Ostman et al 2003). Arable food webs are usually highly complex and dynamic due to spatio-temporal fluctuations in predator and prey densities and coining extrinsic factors such as farming practice and habitat heterogeneity (Macfadyen et al 2011; Rusch et al 2010, 2014) This is especially true for food webs involving generalist predators, many of which are effective natural enemies of pests, but not always constitutive such that they regularly choose from a variety of alternative extraguild and intraguild prey (Davey et al 2013; Eitzinger and Traugott 2011; Kuusk and Ekbom 2010; Lang 2003). A thorough understanding of such interactions is important, but largely rests with the ability to directly track the feeding links through these food webs (Bohan and Woodward 2013)

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