Sniffer bees

Currently in its second year, the European Framework Programme 7 (FP7)-funded project, Prevail, is looking at innovative approaches to improve the detection of explosives and inhibit the use of their precursors. One of these methods is the use of sniffer bees.

Prevail is coordinated by the Swedish defence research agency and involves 10 partners from across Europe, including UK company Inscentinel. Recently, Inscentinel has developed a detector, the Vasor 136, which contains 36 honey bees capable of recognising up to six different chemicals at the same time. This should open up sniffer bee technology to a host of other unusual applications.

Training school

Honey bees have 170 odour receptors in their antennae, compared with a mere 62 in mosquitoes and 79 in the common fruit fly. In their everyday lives they use these to identify a host of different smells so that they can find nectar sources at any time of the year. They learn to associate the smell of a flower with nectar, so that when they find a similar flower in another place they know they will find nectar there.

This ability of honey bees to learn odours was recognised by Jeff Bitterman and his colleagues in the Békésy Laboratory of Neurobiology, Honolulu, Hawaii, US, in the early 1980s. The scientists went on to train bees in the laboratory by classical Pavlovian conditioning. When a bee’s antennae is touched with a cotton bud dipped in a sugar solution, it automatically extends its proboscis, or tongue, to drink.

To train a bee to recognise a particular odour, say a mixture of volatile chemicals or a single compound, all the researchers had to do was expose the bee to the odour for a few seconds, at the same time touching its antenna with a sugar solution, and then reward it with sugar when it extends its proboscis. After five or six rounds of this the honey bee responds by extending its proboscis as soon as it detects the odour – it is now fully trained.

In 2000, following a programme of research on training honey bees to recognise components of the odour from oilseed rape flowers, a group of scientists from Rothamsted Research, UK and CNRS, Paris, with the support of Unilever, set up Inscentinel to find ways of exploiting the olfactory acuity of honey bees in commercial applications.

At around the same time scientists from the US Defence Advanced Research Projects Agency, working at Los Alamos National Laboratory, were training bees to detect 2,4-dinitrotoluene, a chemical residue left by several different types of bombs. They were experimenting with free flying, trained honey bees fitted with tiny radio transmitters so that they, and the bomb, could be found when they swarmed. The scientists also used 2,4,6-trinitrotoluene (TNT), which is present in the majority of anti-personnel land mines, and found that trained bees could detect it at parts per trillion, a considerably lower concentration than could be detected by dogs.

At present, dogs are used to sniff out bombs and explosives in crowded airports and ports – bees are probably not what you would want in an airport but could be used in a war zone. Electronic devices – electronic noses – perform as well as dogs in a controlled environment but give too many false positive responses in the field. However, sniffer dogs are expensive to train and keep, possibly as much as £70,000 in the first year and £50,000 in subsequent years, and they need to be taken care of by handlers.

Sniffer bees have the advantage that they can be trained in less than an hour, taken out on assignment and returned to the hive to continue their day job – making honey. They do not need to be taken out for walks twice a day and, for most of the time, they do not require feeding – their food comes from the wild. However, sniffer dogs are excellent at searching and may even have a deterrent effect on terrorists by virtue of their physical presence whereas the bees, in containment, need to be taken to the suspect person or package to perform their task. Once there, however, they are as sensitive, or better, than dogs.

To overcome the logistical and practical problems of using bees in these environments, scientists and engineers at Inscentinel are working to automate the whole process – from taking honey bees from the hive, loading them into cells with the necessary electronics to observe the proboscis extension response (PER) and a heater to keep them warm in cold environments, to training them and then loading them into the Vasor 136.

This hand-held detector, which looks like a car vacuum cleaner, draws clean filtered air constantly over a rack of 36 trained bees and then when a button is pressed the suspect air is drawn over them for just 6 seconds. Any bee that extends its proboscis triggers a signal to the digital readout on the top of the instrument, so that it is possible to see how many and which ones are responding positively. The automatic unit will be capable of conditioning 100 bees/hr.

Future applications

Apart from security applications, researchers at Inscentinel are looking to identify other possible uses for the sniffer bee technology. The smuggling of narcotics is a huge problem worldwide and probably the main use of sniffer dogs. At Inscentinel, we have used honey bees to detect concealed cocaine, heroin and 3,4-methylenedioxy-N-methylamphetamine (MDMA) in small amounts. They can also sniff out cigarettes once they have been trained to recognise low levels of nicotine. The only limit to their use is the presence of a volatile chemical marker in the target substance – they would not be able to detect precious metals or jewels but then nor would dogs or electronic noses. As well as deployment in airports, the bees can be employed in ports to detect explosives, drugs and other illegal substances in cargo containers, something which is extremely difficult to do at present because it is mainly done using X-ray screening.

In 2010, there were 1.4m deaths from tuberculosis, mostly, but not exclusively, in developing countries. Scientists at Inscentinel, with collaborators at the New Zealand Institute for Plant and Food Research, are developing methods to use trained bees to detect tuberculosis marker compounds on the breath of people who, as yet, show no signs or symptoms of the disease. If successful, this will offer the prospect of mass screening of populations and with such early detection, medical intervention can prevent many of the deaths and also help to stop the spread of the tuberculosis mycobacterium. Experiments have also been conducted on the early detection of pancreatic cancer, using bees trained on specific marker compounds present in urine.

Other projects under investigation include the detection of boar taint in pork, by looking for traces of androstenone, indole and skatole emanating from the meat; and the early detection of dry rot fungus in stately homes, using specific marker chemicals.

We know when food ‘goes off’ because we can smell it and if we can, then so could the bees and they could probably do it at a much earlier stage than us. There is thus a great potential for the early detection of food contamination. In a recent investigation at Rothamsted, we trained bees to recognise some of the volatiles produced by oranges that were infested with Mediterranean fruit fly larvae. In laboratory tests, the bees could discriminate between healthy and infested fruits. Unfortunately, they were not able to do the same at the orange processing plant but their use in other fruit/pest combinations could be successfully exploited.

It looks like the humble honey bee has even more to offer than its honey.

Keith Chamberlain is a chemical ecologist at Rothamsted Research, Harpenden, UK, and Maxim Rooth is a senior R&D scientist at Inscentinel, Harpenden, UK.