Sustainable pest control - comparing tritrophic interactions in organic and conventional production systems

One of the greatest problems facing the world is producing enough food of the desired quality whilst maintaining an environment rich in biodiversity. There are often many trade-offs between highly intensified conventional agriculture and more extensified organic agriculture. Within the UK, there is a desire to become less intensive and organic agriculture is becoming more widely adopted and desired. However, there are many anecdotes and folklores surrounding organic agriculture and there has been little vigorous scientific investigation. This needs to change if this method of agriculture is to be even more widely adopted, and hopefully optimised so as to be more sustainable economically as well as environmentally. We propose to conduct a detailed scientific investigation into whether organically grown cabbages are better defended against pest insects than their conventional counterparts. We will also explore the chemistry (taste, nutrition and smell) of cabbages grown organically and conventionally in order to allow us to study the mechanisms behind any observed differences in pests, and also to address some of the issues frequently raised about the chemical 'quality' of organic produce. Insects destroy 14% of all food in spite of billions of pounds of insecticide being used every year. Growing cabbages organically is very hard due to significant pest damage, yet there is a strong desire for organic cabbages as conventional crops receive a lot of insecticide. We will use lab and field studies to see whether organic plants defend themselves better and are less attacked/damaged by pests. We will use a model system involving two major pests (a chewing caterpillar, the diamondback moth, and a sucking/piercing greenfly, the cabbage mealy aphid) and the natural enemies of these pests, in order to conduct scientific investigations which will allow us to determine whether organic cabbages are better defended, and if they are why? Finally, we will develop a mathematical model which will explain our observations in numbers. What is really useful with the model is that it will allow us to run many more experiments on a computer saving us lots of time and money. This will allow us to develop a picture of how to optimise the positives of our system whilst reducing the negatives. The approach we will adopt on our model system could be extended to other crops and will hopefully ensure that we can produce the quantity and quality of food we desire whilst leaving a smaller ecological footprint.

This cross-disciplinary project will combine chemical, ecological and modelling techniques to determine whether cabbages grown under an organic regime differ in terms of pest dynamics and plant chemistry. There is increasing pressure to de-intensify agricultural practice and organic approaches are becoming more popular and widely adopted. However, there are very few, if any, detailed scientific investigations into the claims made about improved pest control, reduced environmental impact and better nutrition associated with organic produce. We will focus on a well-studied and important model system centred around the production of cabbages Brassica oleracea. We will study tritrophic interactions on cabbages grown conventionally and organically at a range of scales from small-scale lab studies through to large scale field trials. We will extend the spatial-temporal complexity by utilising modelling to describe what we observe and to predict what affects we might see under a range of future production scenarios. A range of techniques pioneered in our labs will be used to study bitrophic and tritrophic interactiosn on cabbages using the model systems (Brevicoryne brassicae./Diaretiella rapa and Plutella xylostella/Cotesia plutellae. In addition to studying the population dynamics of the lab-based studies, we will also assess pest/parasitoid dynamics under field conditions at an experimental farm. This will allow us to determine how the two production (organic and conventional) systems affect pest dynamics (in bitrophic studies) and biocontrol (tritrophic studies). This provides a good link back to lab studies and provides empirical data which can be used to construct the model we will develop. Detailed chemical analysis will be performed on the cabbages (nutritional and volatile profiles) in order to determine causal relationships between bitrophic and tritrophic interactions and chemistry. This will also allow us to explore the role of parasitoids as biosensors capable of detecting change and thus widen the potential significance of this research project.