In a project funded by Defra last year, biocontrol specialists investigated interactions among mites on strawberry, to determine how the presence of different predators affects the occurrence of pests. The team has also identified a number of insect species which are increasingly damaging strawberries, including species of thrips and aphid, and is working on HDC-funded projects to identify predators able to control them.
“Many species of predatory insects found in strawberry plants consume a range of prey species,” says organics expert Jean Fitzgerald. “The availability of these alternative prey species may affect the degree of control the predators exert over particular pest species. For example, one of the commercially available predatory mite species, Neoseiulus cucumeris, is sold for control of thrips as well as tarsonemid mites. A commercially available predatory insect, Orius laevigatus, is able to feed on thrips and aphids. A range of naturally occurring predators is found in strawberries and may contribute to biocontrol of pests.”
“However, work on other crops has shown that adding predator species to existing predator-prey systems does not necessarily increase the suppression of herbivore species, and may lead to an increase in some species,” Fitzgerald claims. “Biocontrol may be disrupted by intraguild predation, and by other indirect food-web interactions. In the current Defra-funded research project we are investigating the feeding relationships among a complex of predators, both naturally occurring species and those released for biocontrol, and their prey on strawberries. We are looking at consumption patterns of these predators in laboratory experiments and comparing their effectiveness as control agents in the field. We are also using molecular techniques to determine what field collected predators have recently eaten. This research will enable us to add to the food web we have produced for mites and will optimise pest management systems in strawberry production.”
Fitzgerald’s team is also involved in an EU interreg project, Transorganic, with GABNOR (Groupement des Agriculteurs Biologiques du Nord Pas de Calais and FREDON (Fédération Régionale de Défense contre les Organismes Nuisibles). The aim of the project is to increase the number of beneficials in strawberries.
“We are investigating the use of floral strips to attract beneficial arthropods into the plantation,” says Fitzgerald. “These floral strips may provide nectar and pollen to beneficial species, or other arthropods feeding on the plants may act as alternative prey to lure the beneficials into the area. When these have been consumed the predators may then move into the strawberry plantation.”
In addition EMR is investigating the use of artificial refuges to provide shelters for beneficial arthropods. Fitzgerald says the project involves comparing commercial designs with more primitive hand-crafted options. “We are comparing different designs of refuge for both flying arthropods such as lacewings and ladybirds, and ground living arthropods such as predatory ground beetles,” she says. “One design of simple refuge for flying insects consists of a plastic drinks bottle with its bottom removed, filled with a roll of corrugated cardboard and hung on a stake. A design that we are testing for ground dwelling predators is a grooved slab of wood held slightly above the ground surface.”
Fitzgerald emphasises that all work orientated towards organic production is equally beneficial for growers using conventional methods.
PESTS
Entomologists at EMR have made further advances regarding soft-fruit pests, according to research leader Jerry Cross. EMR has been working in collaboration with David Hall in the Chemical Ecology group at the National Resources Institute on projects looking at pheromone identification for pest control. “We have just identified the sex pheromone of the raspberry cane midge which is quite a serious pest of raspberries,” says Cross.
“At the moment the growers have to control it using the chemical chlorpyrifos. They apply it as a routine in spring, using a forecasting model based on temperatures from ADAS. These forecasts don’t tell whether you’ve got the pest and whether sprays are needed. They only apply to the first generation and cane midge can build-up and cause damage in the second and third generations.”
Having gauged that the sex pheromone is highly attractive to midges, Cross says his research team is now going to embark on a series of experiments, to try to use the pheromone to control the pest by way of three different strategies: mating disruption, which involves confusing the males by releasing the pheromone from numerous points in the plantation; mass trapping, achieved by using it to lure the midges to a trap where they are killed physically, for example, drowning in liquid; and lure and kill, leading the midges to a small target device surface treated with insecticide.
Cross’ team, funded by Horticultural Development Council, has also been working on alternative chemicals of control for raspberry beetle, which is the fruit’s main pest, he says. “Even a minimal presence of the beetle or damage can lead to a rejection of fruit in the fresh market. Again, growers are using chlorpyrifos to control it but as this is an organophosphate insecticide it is toxic to humans. We conducted trials of alternatives last year and have identified three alternative insecticides which are safer and hopefully by using them we won’t get residues at harvest.”
Chlorpyrifos has to be sprayed when, or just before, the fruits turn pink, and pesticide residue analyses have shown that as much as 30 per cent of all harvests contain chlorpyrifos residue traces, Cross claims. As such, he has been working to identify more consumer and environmentally friendly forms of control.
Regarding strawberries, Cross and his partners at the Natural Resources Institute have identified the pheromone of the European tarnished plant bug, a species of the Lygus bug. “It is the first time anyone has made an attractive lure for a species of Lygus bug, so we are quite excited.” Cross added that research has been carried out in other countries including the US for many years on similar species without success. “The breakthrough was releasing the pheromone in very tiny amounts from glass micro-capillary tubes,” he said. “A practical pheromone dispenser for use by growers now needs to be developed.”
EMR’s entomology work is one of the company’s particular success stories since its split from HRI last year, says chief executive Colin Gutteridge. Since being privatised on April 1 2004, the company has made a pleasing profit and Gutteridge says it is making steps to become less reliant on public sources of funding, by developing tangential assets.
And there are additional projects in the pipeline. While its current programmes are to remain an integral part of EMR’s raison d’etre, Gutteridge is intending to broaden the company’s horizons. “One challenge is to try and broaden our scientific activities to do more research work further up the food chain. At the moment it stops at the bulk storage of food. We want to develop that and work right through to the consumer,” he says.
Although this plan is still a while off fruition, Gutteridge says it should not be difficult to implement. “We have got the relevant technology in place. It is simply a question of funding. Over the next few years there will be a change in the mix of disciplines we have. We will continue to do the type of work we are doing for the industry but aim to do more work with respect to the quality and shelf-life, packaging and consumer acceptance of fruit.”
This new venture is a reflection of Gutteridge’s conception of EMR within the industry at large: “I believe EMR is part of the horticulture industry and its future depends on the horticulture industry being successful. So philosophically we are as much interested in the commerce of the industry as the science of it and are hoping to be a meeting point for decisions about horticulture in general.”
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