Biological crop protection: a new 'slow down/speed up' strategy for aphid management

Aphids are important insect pests of a wide range of crop plants. For crops grown outdoors, including field vegetables and arable plants, the standard way of managing aphids has been to apply synthetic chemical insecticides. Originally these were very effective, but excessive use of pesticides has caused some key aphid pests to evolve resistance. At the same time, there are concerns about the environmental impact of pesticide use, which has led to many products being withdrawn from sale. Such as the neonicotinoids. This has left farmers with few workable options for controlling aphid pests which have now become a major threat to farm production. A sustainable form of aphid management that can be used by farmers is urgently needed.

To make crop protection more sustainable and less prone to resistance, it is better not to over-rely on any one intervention. Diversification of tactics can be achieved through Integrated Pest Management (IPM), a way of controlling pests by combining different, complementary control agents in an environmentally sensitive way. These should principally be biological methods that include breeding pest resistant crop varieties, the use of natural enemies such as parasitic wasps, together with 'biopesticide' products based on beneficial microbes or natural products. These crop protection tools are safe for people and the environment and so they should provide a better form of crop protection. Chemical insecticides do have a role in IPM, but they are used only when necessary in order to reduce the chances of pests evolving resistance to them. Unfortunately, because farmers have been so reliant on chemical insecticides as the principle form of pest control, there is currently no effective IPM system in place yet for the majority of aphid pests in field crops. The development of IPM has been held back by a lack of new pest control agents and the knowledge about how they interact when used together.

The project involves five interlinked pieces of work. (1) Data on gene expression from multiple brassica crop types is used to identify plant lines that have a high probability of showing resistance to aphids, and this will be confirmed in experiments with aphids feeding on plants in the laboratory. The gene expression data will allow genetic makers to be developed that can be used by seed companies in their plant breeding programmes. (2) The biological basis for plant resistance to aphids is determined using a series of laboratory and field experiments. (3) Research on fungal biopesticides is done to determine how their performance is affected by the environmental conditions in the field, and also to understand how crop plant resistance affects their efficacy against aphids. (4) Complementary research looks at how different types of brassica plant, with resistance to aphids, affect the function of parasitic wasps, which are important natural control agents of aphids on field crops. (5) The interaction of resistant crops, fungal biopesticides and parasitoids are studied in the field in an IPM system.

The aim of this project is to develop the new knowledge and tools needed for an IPM system for aphid pests of field crops. The work centres on the peach potato aphid, Myzus persicae, which is a pest of a wide range of crops and has evolved resistance to many commonly used insecticides. The experiments involve vegetable brassicas and oilseed rape but the intention is to extend the system to other crops (sugar beet, potatoes) in future research. The research is based on a hypothesis that brassica plants with partial resistance that slows down aphid development makes the pest more susceptible to biological control agents and speeds up control with biopesticides and parasitic wasps.

The project will benefit farmers and growers and others in the supply chain. The general public will benefit from improved food security and better care of the environment.

This project will underpin the development of a 'slow down / speed up' IPM system for aphid pests of field crops that combines plant breeding and biological control, focusing on the peach potato aphid, Myzus persicae. Our approach involves slowing down the growth rate of pests while speeding up the performance of their natural enemies. We will investigate the hypothesis that brassica genotypes with partial resistance that slows down aphid development makes the pest more susceptible to biological control agents including biopesticides and parasitoids.

Studies have shown that defence responses in Arabidopsis against M. persicae are based around phytohormone signalling pathways and the phytoalexin camalexin. Expression analysis of gene homologues in Brassica accessions indicates that identifying partial resistance to M. persicae in Brassica crop breeding material is highly likely. The project explores how this partial host-plant resistance can be combined with biocontrol agents

The research has 5 components: (1) Candidate Brassica genotypes with potential resistance will be confirmed using a combination of transciptome analysis and phenotyping experiments. (2) The molecular basis for partial resistance to M. persicae will be investigated, informed by experiments that quantify aphid feeding and development on Brassica genotype breeding lines with aphid resistance markers. (3) Fungal biopesticides will be evaluated against M. persicae on resistant brassica genotypes and research will be done to quantify how biopesticide performance is affected by the fluctuating environmental conditions occurring in field crops. (4) The responses of parasitoids to volatiles from aphid-infested Brassica genotypes will be quantified and the role of cis-jasmone in parasitoid attraction will be elucidated. (5) Field experiments will then be done to measure aphid control on different Brassica genotypes following treatment with fungal biopesticides, parasitoids and cis-jasmone.

This project will provide new knowledge and tools that will allow an Integrated Pest Management system to be developed for aphid pests of field crops. This particular project will concentrate on Myzus persicae feeding on brassicas. The project will benefit farmers and growers, crop breeding companies, biopesticide producers, agronomists and others in the supply chain. The general public will benefit from improved food security and better care of the environment.

Myzus persicae is one of the most important crop pests worldwide and causes economic losses on a wide range of crops. It is very difficult to control using a conventional approach because of widespread multiple pesticide resistance. At the moment, farmers rely on neonicotinoid pesticides but restrictions of the use of certain neonicotinoids on flowering crops, which look set to be extended to all field crops, will leave farmers with very few effective conventional pesticides. The development of a new approach to aphid pest management is one of the highest priorities for farmers, growers and policy makers.

Replacing routine applications of synthetic chemical insecticides with a biological control-based IPM system should result in fewer negative effects of excessive pesticide use on the environment, and give improved sustainability of production. The system will avoid the risk of the crop harvested having insecticide residue levels that exceed official limits.

The project will produce genetic markers for Brassica crop improvement as well as identifying partially resistant Brassica accessions. Crop breeding companies will be able to use these in marker-assisted selection to incorporate partial resistance into commercial Brassica varieties. We will also investigate aphid biocontrol with fungal biopesticides and parasitoids. Crop protection companies are very interested in developing and using fungal biopesticides, natural enemies and other biocontrol products on field crops and this research will be of obvious benefit to them.

Importantly, by taking an IPM approach, we will not be seeking a single 'silver bullet' solution for aphid pests, but rather the aim is to combine different pest management tools in complementary ways, ideally by making use of synergies between them. To this end we will provide new information on (i) the induction of innate immune pathways in Brassica by entomopathogenic fungi; (ii) attraction of parasitoids to Brassica genotypes with partial resistance to aphids; and (iii) the combined effects of partial resistance, fungal biopesticides and parasitoids (including use of cis-jasmone as an attractant) in an IPM system. The potential threat of hyperparasitism in field crops will be investigated. This approach has not been used before for aphids on field crops and represents a step change in pest management science.

Our approach will also help open up the market for biocontrol by improving our knowledge on how environmental conditions in the field affect biocontrol agent performance, and by pioneering a new approach to improve the effectiveness of biocontrol agents by combining them with host plant resistance. This will have a significant positive effect for the biocontrol industry. This currently represents only 5% of the total crop protection market but it has a compound annual growth rate of 15% (compared to 3% for conventional pesticides) and is estimated to be worth $7 billion by 2022. At the moment, most of the biocontrol industry in Europe is based around protected cropping, but the largest potential market is in field crops. Sales of insecticides in Europe (most of which are used on field crops) are valued at >800M Euros p.a. (European Crop Protection Association statistics). Even if biocontrol agents used in the field obtained just 5% market share this would be worth 40M Euros p.a., and given that biopesticides cost on average 5M Euros to develop this would be a valuable return on investment.