Identifying key predators and their role in canola insect pest suppression

Project Summary

Background

Natural enemies provide a key ecosystem service by suppressing insect pest populations (Daily 1997). In the US, an estimated annual cost savings of $4.5 billion (USD) is attributed to natural enemies predating on native pests (Losey and Vaughn 2013). These services can be improved through conservation biological control which involves the maintenance or enhancement of natural enemies present in the agroecosystem (Landis et al. 2000; Gurr and You 2016). To design conservation biological control strategies to enhance IPM on the Prairies, a thorough understanding of the relationship between predators and pests in the agroecosystem is needed.

Many predators exist in the canola agroecosystem. Spiders (Araneae), ground, rove and ladybird beetles (Coleoptera: Carabidae, Staphylinidae, Coccinellidae, respectively), lacewings (Neuroptera: Chrysopidae), syrphid flies (Diptera: Syrphidae), and nabid and pirate bugs (Hemiptera: Nabidae, Anthocoridae) are some of the more common predators in canola fields, but their impact on pest species has not been well investigated (Gavloski et al. 2011). Predators are usually generalists that feed on a wide variety of insects depending on life stage and time of year (Symondson et al. 2002). Although research on the contribution of predators to IPM has increased recently, few studies have measured the impact of predators on pest populations partly because of challenges in accurately determining the prey items that predators consume (Furlong and Zalucki 2010). Recent advances in molecular techniques now allow molecular-gut content analysis to determine the range of prey items consumed (King 2008; Pompanon et al. 2012; Furlong 2015; Gurr and You 2016). Once the diet of predators is known, then manipulative experiments can quantify the impact of predators on pests and develop dynamic action thresholds in IPM programs.

The use of molecular techniques to determine prey remains in predator guts has progressed rapidly (Furlong 2015). It is now possible to characterize all of the prey (rather than a few target species) consumed by predators using high-throughput sequencing technologies (Roslin and Majaneva 2016; Eitzinger et al. 2019). Molecular gut-content analyses have been used to investigate trophic linkages within food webs (Sheppard and Harwood 2005; Traugott et al. 2013; Staudacher et al. 2016) and to identify key insect predators of pests (e.g. Floate et al. 1990; Chen et al. 2000; Fournier et al. 2008).  These studies demonstrate that generalist predators can exhibit considerable preference for certain prey items (Staudacher et al. 2016); can consume other predators (Roubinet et al. 2017); and that alternative prey disrupt predation on pest species or can be important to sustain predators when pest populations are low (Kuusk and Ekbom 2010, 2012). Given the diversity in predator-prey interactions and the context in which they occur, predator-prey relationships must be thoroughly investigated before the role of predators in IPM can be quantified.

Molecular gut content analysis has been used to evaluate the impact of predators in Brassica vegetable crops (Hosseini et al. 2012; Furlong et al. 2014), but remains to be applied in canola (Brassica napus). The most well studied predator community in Prairie field crops are ground beetles (Holliday et al. 2014), but the few studies that have characterized predator-prey interactions have been conducted in pulse crops (Vankosky et al. 2011) and cereals (Floate et al. 1990). For foliage predators, based on molecular gut content analysis, nabid bugs and lady bird beetles, are key predators of cereal leaf beetle (Kheirodin et al. 2019). Predation pressure in canola fields may be unequal, with certain predatory species contributing to the majority of pest management (e.g. Prasad and Snyder 2006), thus it is imperative that the relationships between different predators and their prey be determined. 

Objectives

The goal of this project is to identify the key natural enemies in the canola agroecosystem by detecting pest insect DNA in guts of predators, and to begin quantifying their pest suppression ability.

The specific objectives are to:

1. Establish a comprehensive record of the insect community in Central Alberta canola fields.
2. Develop next-generation DNA sequencing methods to identify the breadth of predator-prey relationships in canola fields.
3. Develop a multiplex PCR method to identify common canola pests in the diet of various generalist predators.
4. Quantify the impact of key predator species on pest populations in laboratory bioassays.

Project benefit

The pest suppression ability of insect natural enemies can form the cornerstone of integrated pest management programs. This project will fill a knowledge gap by identifying the key natural enemies of canola pests in western Canada and begin to quantify their impact on pest populations. Currently, most of the predator-pest relationships are hypothesized based on anecdotal evidence, but this study will conclusively determine these relationships and identify the most important natural enemies in typical canola prairie agroecosystems.

This project is focused on characterizing the community of insects associated with canola in Central Alberta to provide baseline data on predators and pest species. Using these samples, a next-generation sequencing approach will be developed to identify trophic interactions between predators and prey species (including pests) to gain a comprehensive understanding of the invertebrate food web and community interactions in canola. Once the key predators have been identified within canola fields, a targeted multiplex PCR approach will be used to determine the predation pressure on pest species in Southern, Central and Northwestern Alberta. This approach will allow simultaneous detection of multiple canola pest species within the guts of predators. Finally, the ability of key predators to reduce pest populations (e.g. flea beetles, root maggots, bertha armyworm) will be examined in laboratory cage experiments. This information will provide the foundation for future ecological experiments to determine how to adopt conservation biological control approaches to enhance IPM in canola at the farm level on the Prairies.

This information will be vital to conduct further conservation biological control studies which will aim to enhance the natural pest suppression ability of these predators.  Ultimately, this information will help to increase plant health, reduce unnecessary pesticide use, and support sustainability of the agroecosystem.

Literature cited

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