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THE crime scene: an art gallery in Caracas, Venezuela. The victim lies on her back, riddled with holes. Her beautiful face is ravaged, her body a wreck. This is no one-off, random incident. All the evidence points to a group of suspects who have orchestrated a series of vicious attacks worldwide. Special agents have been trying to get the better of them for many years. Now, finally, it looks as though the good guys may be about to triumph.

What sets this detective story apart is that the victim is not a person; it is an 18th-century wooden statue of the Virgin Mary, the Immaculada. And it is in danger of being turned to sawdust by an infestation of beetles. The French painter Eugene Delacroix once said: 鈥淭he first virtue of a painting is to be a feast for the eyes.鈥� This statue is part of the estimated one-third of Venezuela鈥檚 cultural artefacts that have become a feast for bugs. Heat and humidity make tropical countries an ideal breeding ground for these pests, but the problem is not confined to equatorial regions. Across the globe, insects, bacteria and fungi are ripping into old masters, turning statues to dust, and ruining paintings and historical documents.

Now a new breed of art conservator is fighting back. Combining the skills of a detective and a molecular biologist, they are working to reveal the precise identities of the perpetrators, and dreaming up ingenious ways of foiling them. The very latest of these is soon to be tested on the Immaculada. Her salvation would not only be a major achievement for the Venezuelan scientists pioneering the technique, but would mark an important breakthrough in the battle against the pests everywhere that threaten the fabric of human cultural heritage.

People have been trying for centuries to protect artworks from decay, but the methods of pest-control tended to bring their own problems. For a start, fumigants that are toxic enough to kill bugs are often harmful to humans as well. And some treatments damage the environment. Methyl bromide, for example, was once very popular, but its use is now restricted in many countries because it depletes the ozone layer. Other fumigants, such as Vikane, which is used on termites in particular, harm the art they are supposed to be saving, reacting with paints and varnishes to cause discoloration. 鈥淭he field is filled with a history of chemicals that have been tried and then found to cause damage,鈥� says cell biologist Robert Koestler, who is director of the Smithsonian Center for Materials Research in Maryland.

In an attempt to overcome these problems, Koestler and others realised they needed to target their treatments more effectively. And to do this they first had to hone their skills in identifying the suspects.

Take fungi, for example. The fallout from fungal attacks on paper can make grim reading. 鈥淭he black stain left by some fungi is particularly difficult to get rid of,鈥� Koestler says. Enzymes can be used to remove the melanin deposits, but because melanin is basically lignin, removing it also destroys the lignin in the paper, he says. And that can cause the paper to disintegrate. Knowing which fungus is to blame could help, however, because different strains produce melanin with slightly varying structures. This opens up the possibility of finding enzymes that will target the fungal melanin and ignore the lignin in the paper.

Before moving to the Smithsonian, Koestler was a conservator at the Metropolitan Museum of Art in New York. His team there included microbiologist MariaPia Di Bonaventura, who in 2000 began working on a project to identify the strains of fungi that were staining drawings by the 19th-century American artist Louis Comfort Tiffany. Traditionally, art-infesting microbes are cultured to aid identification. 鈥淭his has its limitations,鈥� says Di Bonaventura, who is now at the American Museum of Natural History in New York. 鈥淣ot all the viable ones will grow under selected laboratory conditions, and false positives can arise 鈥� a single extraneous spore that floated by can yield an erroneous result.鈥� Her answer was to isolate fungal DNA from the drawings then sequence it and compare the sequences with those in the US National Institutes of Health GenBank database. This revealed that species of Chaetomium were in the frame for the grey and black stains, while brown stains were produced by species of Cladosporium. Knowing that these two fungal types are producing the spots means treatment can be focused on their removal, Di Bonaventura says. Koestler, meanwhile, is looking for better ways to remove the stains produced by specific fungi.

鈥淎cross the globe, insects and bacteria are ripping into old masters and turning statues to dust鈥�

The simple idea of using DNA sequencing to identify infestations has huge potential. In another study, Christopher McNamara of Harvard University and his team used sequencing to find out what was eating stone blocks and carvings in Mexico鈥檚 Mayan ruins. Previous studies revealed microbes living on the surface of these stones, but last year McNamara announced that DNA sequencing had uncovered a different community of organisms within. Further tests revealed that these Actinobacteria are causing the damage by breaking down the limestone as they grow. It is still not clear how to kill them. 鈥淎ny attempt will encounter serious difficulties in delivering the treatment to the target,鈥� McNamara says. But at least conservators have a clearer idea of what they are dealing with.

Even in cases where the culprit itself cannot be found, DNA analysis can help to track it down. At UNU-BIOLAC, a UN university in Caracas, director Jos茅 Ramirez and his colleagues have been using the technique on faecal remains. 鈥淒NA typing is easy to perform and cheap, and it can be done on just one particle of faeces,鈥� Ramirez says. 鈥淲e have found no cross-reaction with bacteria or other organisms that may be present in the bug鈥檚 guts.鈥�

These faecal mug-shots can also help in cases of mistaken identity. For example, cigarette beetles and odd beetles 鈥� both common pests 鈥� are omnivorous, which makes them potential museum-wreckers. 鈥淭o a non-specialist the two look similar,鈥� says Ruth Norton, chief conservator at the Field Museum in Chicago, Illinois. But the odd beetle is far more pernicious. 鈥淚t can go through many moults, increasing or decreasing in size depending on food availability. So it can have a very extended lifespan and can survive food scarcity.鈥� Simple DNA analysis, either of the beetles themselves or of their faeces, could allow museum curators to distinguish between odd beetles and cigarette beetles. If they find odd beetles at work, they will know that they need a comprehensive, long-term control strategy to monitor and eradicate them.

Most curators continue to use chemicals to keep pests in check, but being able to identify the offending organisms precisely is helping in the development of non-toxic alternatives. Koestler is among those exploring the possibility of suffocation. His preferred method is to seal an infested artwork inside a plastic bag, then pump argon in and oxygen out. For optimum results he needs to know exactly how long the treatment should last, so he and other researchers have been investigating the breathing and death rates of a wide range of insect pests. Nieves Valentin, working at the Getty Conservation Institute in Los Angeles, California, has found, for instance, that at 40 per cent relative humidity and 20 掳C, in an atmosphere where the oxygen has been reduced to less than 300 parts per million and replaced with argon, the old house borer beetle takes at least 14 days to die, while the black carpet beetle perishes in just three. 鈥淯sing this technique, anything that requires oxygen to stay alive will succumb,鈥� Koestler says. 鈥淭hat includes most insects and bacteria, and some fungi.鈥�

鈥淓ven in cases where the culprit cannot be found, DNA analysis can be done on its faeces鈥�

Other researchers trying to perfect suffocation techniques are experimenting with different gases and containers. At the Australian Museum in Sydney, for example, Vinod Daniel uses nitrogen instead of argon. 鈥淟ow oxygen in the chamber is the safest pest-killing technique,鈥� he says. But there is a downside. The technology is expensive, and even more so in humid countries where the higher water content in the atmosphere allows pests to survive for longer without oxygen.

An alternative approach that Daniel and his colleagues are investigating is to 鈥渃ook鈥� the pests. The team found that to kill all the usual suspects, an artefact must be heated to 52 掳C and kept at that temperature for around 6 hours. This sounds expensive, but it needn鈥檛 require ovens, or even a regular electricity supply. The temperature can be achieved simply by placing the infested object in a black plastic bag, inside a clear plastic bag, and then leaving it in the sun. The black plastic absorbs heat, while the clear plastic creates an insulating layer of air, helping keep the temperature inside the bag above the critical temperature even if a cloud should pass across the sun.

This low-tech approach is ideal for museums in developing countries, which is why the Australians have been working with curators from Pacific islands, including Vanuatu and Fiji, to persuade them to adopt it. But heat treatment does have one drawback: the expansion and contraction caused by changes in temperature and humidity can damage the precious artefacts.

Then there is the problem of keeping the bugs at bay once an item has been treated. 鈥淪ome methods may work temporarily, but the chances of reinfestation are much higher in the tropics,鈥� Ramirez says. 鈥淎nd many countries in the tropics do not have the means for artificial climate control. You have to find ways to cure and protect artwork, adapted to that reality.鈥� This has left some conservators looking around for alternative, non-toxic pest eradication methods. The solution they have hit upon is biological control.

The possibilities of this approach were hotly debated last November at a symposium hosted by UNU-BIOLAC and attended by more than 100 delegates from across Latin America and from Europe and the US. 鈥淔ighting biological agents with other biological entities, like bacteria, fungi, other insects and animals, could be interesting as new, 鈥榗lean鈥� control method,鈥� says Benoit de Tapol from the National Art Museum of Catalonia in Barcelona, Spain, who attended the meeting. When it comes to destructive bacteria, Ramirez says, perhaps colonies could be wiped out using viruses or antibacterial peptides such as those found on the skin of certain frogs. But his first trial, on the Immaculada, will involve inoculating the sculpture with Bacillus thuringiensis, a bacterium producing Bt toxin, which is used as a pesticide and produced by some transgenic plants to make them pest-resistant. He hopes the bacteria will not only kill the beetles but that once they are done they will form spores that will remain within the statue, effectively vaccinating it against further attacks.

Virgin territory

Work on preserving the Immaculada began last year with a CAT scan of the 78-centimetre-tall statue to assess the extent of the damage. Ramirez and his team also took a closer look at the statue鈥檚 wood. They found three different types, but so far only the wood used for the body has been identified 鈥� as mahogany. The face and hair were carved from softwoods with characteristics typical of low tropical forests. 鈥淭he fact that the wood scientist could not tell which local plants corresponded to the softwoods motivated us to create a database with information from traditional taxonomy and DNA typing,鈥� Ramirez says.

DNA information on the two softwoods is in the database, awaiting matching to species. Ultimately, Ramirez hopes, the wood database should help conservators rapidly identify species used in other carvings in South America. And by including details on the pests that like to munch on those species, conservators will also be able to assess more quickly which are more likely to be damaging their artefacts. In this case the culprit was easily identified by an entomologist as the wood-boring beetle Calymmaderus punctulatus. Ramirez is hopeful that it will succumb to a strain of B. thuringiensis that produces a toxin called Cry3. His team is now running tests on pieces of wood infected with the beetle and other pests. If the trials are successful, the final step will be to use a combination of CAT scanning and a surgical probe to inject bacteria into the Immaculada.

The uncertainties do not end there, however. It is not even clear whether toxin-producing bacteria could reach all the insects hiding in their tunnels, or how long the bacteria or their spores would survive in wood. And Koestler warns that using bio-toxins in this way could lead to resistant pests. 鈥淏acterial control requires a high moisture content 鈥� if not liquid water 鈥� to keep the bacteria alive. The water by itself may cause significant damage to the object,鈥� he adds.

But Ramirez is optimistic. 鈥淲e don鈥檛 know what the dynamic of the spreading infection will be,鈥� he admits. 鈥淏ut we assume that once one beetle is infected, new bacteria will hatch and spread through the whole artwork.鈥� He feels that he has nothing to lose in trying. Bt bacteria occur naturally in soils, he says, and there is no way they can damage the Virgin. Besides, if the experiment does work, the pay-off may be huge. 鈥淚t could have the bonus of protecting the statue forever from reinfection.鈥�