Horticulture: Managing aphids and virus on lettuce - investigating components of an IPM strategy

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Lettuce is infested by a small number of important pests, the majority of which are aphids. Some of these species of aphid, particularly Myzus persicae and Macrosiphum euphorbiae, are known to transmit plant viruses, which can reduce crop quality and yield. At present, both the aphids and the viruses they can transmit are managed mainly through the application of insecticide treatments. In the UK, over 21,000 hectares of lettuce were treated with insecticides/nematicides in 2019 and over 55% of this area was treated specifically for aphids. Insecticidal control of pest insects is becoming increasingly problematic for growers due to the limited range of effective active ingredients available to them, which may also be limited further by incidences of insecticide resistance. It is apparent that growers need to consider alternative approaches to pest control that might be used alone or in combination with other tools as part of an Integrated Pest Management strategy, which is '... a decision-based process involving coordinated use of multiple tactics for optimizing the control of all classes of pests (insects, pathogens, weeds, vertebrates) in an ecologically and economically sound manner.'. The use of multiple tactics is important, since it is unwise to rely solely on a single tool that applies high selection pressure to the pest, leading to a breakdown in control. Examples of this include selection for insecticide resistance and pests that are able to overcome host plant resistance. Alternative approaches that might be deployed as part of an IPM strategy include host plant resistance, biopesticides (which might be plant extracts, insect pathogens or other substances of biological origin), biological control agents (e.g. predators and parasitoids) and techniques for manipulating aphid host plant finding and host plant acceptance behaviour, including the introduction of additional plant species into the system. The additional components could be a non-host plant/background which can 'interfere' with host plant finding or a 'trap' plant, which would be a more preferred host than lettuce and 'draw the pests away'. In another approach, sweet alyssum (Lobularia maritima) is grown quite widely within crops of organic lettuce in California, the aim being to attract adult hoverflies to feed. The female hoverflies subsequently lay eggs on the lettuce and, once hatched, the larvae feed on aphids. The aim of this project is to assess the potential of several components of an IPM strategy to manage aphids on lettuce crops, separately and together. This will include potential non-host companion plants/backgrounds and 'trap' plants to prevent aphids from colonising lettuce crop plants, biological control using sweet alyssum plants to attract natural enemies, particularly hoverflies, and biopesticides that might decrease the suitability of lettuce as a host plant or reduce the numbers of aphids infesting trap plants. The project will focus on Myzus persicae in laboratory and Tygan House experiments but will take account of all pest aphids in field experiments. The industry partners will assess the feasibility and costs of incorporating additional species into the lettuce cropping system. If any of these approaches appear promising, then much more work will have to be undertaken to develop them and upscale them for commercial use.