Scientists at East Malling Research are working on a cunning way of fighting the raspberry cane midge. When the insect's pheromones are incorporated into a blob of waxy material, it drives the male midge mad with desire.

The male cane midge tries to mate with the blob of waxy material, gets covered in poison, which is enclosed in the bait, and comes to a nasty end. Meanwhile, the raspberries grow beautifully and attain premium prices when they come to be sold in punnets at the local supermarket. This technique is currently at an early stage of development but there are genuine hopes that it might be a practical method of control.

Until recently, most growers were wary of using these sort of biological controls, which were seen as too expensive and unreliable. However, because of consumer fears about pesticides and increasing demand for organic produce, more growers are now looking to biological controls to protect their crops. And biological controls were given a boost last week, when the European Parliament agreed measures that will effectively outlaw a wide variety of pesticides.

There is no shortage of organisms that will kill pests. Many firms sell a large variety of insects - usually supplied at a larva stage. For example Fargro, one of the major sellers in this country, has a range of agents against spider mites. It can offer at least three types of predatory mites and flying midge larvae, which will eat the spider mite. To combat whitefly, it has ranges of parasitic wasps. BCP - the biological control arm of Certis - offers a wide range of nematodes and parasites to do the same job.

These sort of biological controls work well - in the right conditions. However, the right conditions are not always available. Biological controls are heavily dependent on the weather. If it is too cold, the organisms may simply die. If it is too windy or too wet, the organisms may be dispersed. Flies and larvae can be picked off by native species. For these reasons, biological controls have traditionally been more effective when used on protected crops rather than field crops.

Another problem is cost. BCP development manager Claire Sampson says: "A major limitation is economics. If you want to protect wheat against aphids, conventional sprays will cost around £30 an acre (0.4ha). If you try to use biological control, it will cost around £1,000 an acre."

There is also consumer resistance to using certain kinds of biological controls, according to agronomist Kevin Workman of consultancy UAP. He says: "If you're selling the entire plant - as you do with ornamentals - the customer can't distinguish between nasty pests and good predators. They don't want any insect life on their plants."

Using biological controls requires more forward planning. "With conventional pesticides, you can spray when the problem becomes visible. With biological control, you have to do it before the problem arises," says Workman. "Biological control is not an easy route to take."

Biological controls have to be used at the right time. To be used effectively, they have to be used in relatively small numbers throughout the season, so that they always have enough pests to feed on. If they are simply used in large numbers, the control insects will gobble up the pests and then starve to death. They will then have to be replaced when the next pest outbreak occurs. "It's more like a military campaign. You have to know what you're doing," says Workman.

Anyone using biological controls has to devise a careful strategy for using the controls as part of integrated pest management (IPM).

In the past, biological control wasn't always backed by hard evidence. "A lot of it was muck and mystery. People used anecdotal evidence rather than hard facts," says Workman. However, this is changing and research establishments are increasingly gathering data on these new techniques.

Soft fruit

Some kinds of plant are more easily treated with IPM than others. Strawberry plants have been a particular focus for attention. They are grown in huge numbers across Europe - usually in tunnels where pest insects and fungal spores can thrive.

The industry uses a variety of predatory mites against spider mites and thrips, and there are some new controls in the pipeline. Research leader Dr Jerry Cross of East Malling Research says: "We're developing a parasitic moth that can attack strawberry aphids."

He is also working on "pheromone super traps" against strawberry blossom weevil. These traps incorporate the flower's odour and white colour, and the sex aggregation pheromone of the weevil. The result should be irresistible to any weevil. "We hope to get it out within the next two or three years."

In addition to this research, Cross is working on a "super trap" for the raspberry beetle. The trap is a bucket, painted to look like a giant raspberry flower and scented with the aroma of the flower. It seems that the beetles cannot resist this simple lure.

There is also progress in the battle against mildew on strawberries and lettuce. Fargro has recently released a product called Serenade, which contains the bacteria Bacillus subtilis. This product was only recently approved by the Pesticides Safety Directorate (PSD). The bacteria kills the fungal spores and stimulates the plant's natural defenses.

Salad crops

Protected salad crops can also benefit from IPM. Dr Rob Jacobson, who runs his own consultancy, has developed a system for controlling the major tomato pests - leaf miners, mealy bugs and Macrolophus. To stop mealy bugs getting onto the plants, he uses a sticky barrier. He "culls" the Macrolophus to reduce their numbers rather than kill them entirely. In their reduced numbers, they attack other insects rather than the tomato plants. The leaf miners are killed off by collecting natural predators. This system provides a relatively cheap method of biological control.

Jacobson is currently extending this technique for use against all-year-round crops, which are grown hydroponically with supplementary light.

Top fruit

Traditionally, it has been too expensive to protect apples, pears and top fruit with biological control. Workman explains: "If you put larva on apples, they often just get killed or eaten. If there is a major infestation and the trees have to be sprayed, the biological controls will be taken out by the chemicals."

Cross agrees that there are difficulties. "We tried using the parasitic moth Trichogramma to kill codling moth (Cydia pomonella). It worked, but it was ridiculously expensive. The value of the crop wasn't high enough to justify it."

However, trials are taking place. A nematode - Steinernema carpocapsae - is being used to destroy the larva of the codling moth. Because the nematode needs to be kept wet, it can only be used in autumn, when it is raining and when the temperature is above 14 degsC. Other weapons in the biological armoury include pheromone traps and a virus called codling moth granulosis virus.

Common complaints such as scab and mildew can be treated with copper and sulphur compounds. However, this is a difficult process and there are relatively few producers of organic apples.

Field vegetables

Researchers are also looking at biological controls for pests on field vegetables. ADAS is currently trying to see if the Atheta beetle can be used against carrot fly. Meanwhile, Rosemary Collier at Warwick HRI is looking at methods of companion planting to get rid of cabbage fly. She has found that herbs placed next to cabbage are very effective, although she believes that this is due to the green colour. "You get the same effect with green cardboard," she explains.

Warwick HRI is also examining the possiblities of marginal planting - for example, putting strips of wildflowers alongside fields of lettuce. This kind of planting would encourage ladybirds, hoverflies and parasitic wasps, which would then attack aphids.

Similar work is being done by BCP. Sampson says the company is looking at work done in the Netherlands on cabbages. "We need to find out how much land must be set aside for flowers, and do we need to leave flowers in the middle of the field as well as at the edges?"

BCP has also been looking at ornamentals. It has created what is described as a "mighty applicator" for dropping predatory mites onto the plants. This reduces labour and ensures a more even distribution of the predators. The company hopes to use this system for tomatoes.

As everyone in the industry accepts, biological control is not an easy option. It involves a great deal of experimentation and research. However, with the current pressure to reduce the use of conventional pesticides, these sort of methods are likely to find increasing favour in the future.

EU PESTICIDES LEGISLATION

The European Parliament approved the Placing of Plant Protection Products on the Market regulation and the Sustainable Use of Pesticides directive last week (HW, 16 January).

According to an assessment by the UK's Pesticides Safety Directorate (PSD), the new legislation could remove up to 23 per cent of crop protection products. The implications for minor horticultural coops such as carrots, parsnips and onions are potentially very serious because the majority of currently approved herbicides may no longer be available.

The PSD said in its assessment that there is potential for up to 100 per cent yield loss on carrots in the UK. For a full report on the PSD's findings see HW, 19 December.

EMR's Dr Jerry Cross warns that some of the legislation remains unclear: "The lack of definition for endocrine disruptors means there is some uncertainty about which pesticides will be lost."

However, he points out that, while the situation looks negative in terms of fungicides, the number of insecticides for fruit production that will be lost is small.

There is now a need for further research into crop protection. Stockbridge Technology Centre chief executive Graham Ward points out that the new legislation means "we now have no insecticides for brassicas". He adds: "We are looking at how we can emulate what we do indoors on outdoor crops. But it will mean lower production at higher cost."

TYPES OF KILLER

Two main types of insects are used to reduce pest numbers on crops.

Predators These eat the pests. Examples are the various predatory mites that eat other mites - and often go on to eat each other.

Parasitoids These usually lay their eggs in the host insect. After a while, the eggs hatch out, killing the host.

Because these are naturally occurring, native creatures, they do not require approval for use. However, it means that they cannot be patented, so firms tend to be secretive about new developments.