The scene of the crime is an art gallery in Caracas, Venezuela. The victim lies on her back, riddled with holes. This is no one-off: all the evidence points to a group of suspects who have orchestrated a series of vicious attacks worldwide. Special agents have been tracking them for years.
What sets this whodunit apart is that the victim isn't a person; it is an 18th-century wooden statue of the Virgin Mary, the Immaculada. And it's in danger of being turned to sawdust by beetles. The statue is part of the estimated one-third of Venezuela's artefacts that have become a feast for bugs.
Heat and humidity make tropical countries ideal breeding grounds for these pests, but the problem is not confined to equatorial regions. Across the globe, insects, bacteria and fungi are ripping into Old Masters, statues, paintings and historical documents.
Now, a new breed of art conservator is fighting back. Using the skills of a detective and a biologist, they are revealing the precise identities of the perpetrators and dreaming up ingenious ways to foil them - one of which is to be tested on the Immaculada.
People have tried for centuries to protect artworks, but methods of pest control brought their own problems. Fumigants can harm humans, and some treatments damage the environment: methyl bromide, for example, depletes the ozone layer. And some damage the works themselves. "There's a history of chemicals that have been found to cause damage," says the cell biologist Robert Koestler, the director of the Smithsonian Center for Materials Research in Maryland. Koestler and others realised that they needed to target their treatments more effectively. And first, they had to hone their skills in identifying the suspects.
Take fungal attacks. "The black stain left by some fungi is particularly difficult to get rid of," Koestler says. Enzymes can be used to remove the melanin deposits, but because melanin is basically lignin, removing it destroys the lignin in the paper. That can cause the paper to disintegrate. Knowing which fungus is to blame could help, because different strains might 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 the microbiologist Maria Pia 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.
Di Bonaventura, now at the American Museum of Natural History in New York, isolated fungal DNA from the drawings, sequenced it and compared the sequences with those in the US National Institutes of Health GenBank database. This revealed that species of Chaetomium were in the frame for grey and black stains, while brown stains were produced by species of Cladosporium. Knowing this means that treatment can be focused on the stain's removal, Di Bonaventura says.
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 Mayan ruins in Mexico. Studies revealed microbes on the surface of the stone, but last year, McNamara said DNA sequencing had uncovered a different community of organisms within, which were breaking down the limestone as they grew.
But it's still not clear how to kill them. "Any attempt will encounter serious difficulties in delivering the treatment to the target," McNamara says. But at least he has a clearer idea of what he's dealing with.
At UNU-Biolac, a UN university in Caracas, director José Ramirez and his colleagues have used the technique on faecal remains. "DNA typing is easy to perform and cheap," Ramirez says. Faecal "mugshots" like these can help in cases of mistaken identity.
Cigarette beetles and odd beetles, which are common pests, are omnivorous, which can make them museum-wreckers. "To a non-specialist, the two look similar," says Ruth Norton, the chief conservator at the Field Museum in Chicago. But the odd beetle is far more pernicious. "It can have a very extended lifespan and survive food scarcity," Norton says. Simple DNA analysis could allow curators to distinguish between odd beetles and cigarette beetles. If they find odd beetles at work, they'll know they need a comprehensive, long-term control strategy.
Most curators still use chemicals to keep pests in check, but being able to identify the organisms precisely is helping in the development of non-toxic alternatives. Koestler is exploring the possibility of suffocation. His preferred method is to seal an infested artwork in a plastic bag, then pump argon in and oxygen out. He and other researchers have been investigating the breathing and death rates of a wide range of insect pests.
Nieves Valentin of the Getty Conservation Institute in Los Angeles has found that at 40 per cent relative humidity and 20C, in an atmosphere where 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. "Using this technique, anything that requires oxygen to stay alive will succumb," Koestler says.
Other researchers are experimenting with different gases and containers. At the Australian Museum in Sydney, Vinod Daniel uses nitrogen instead of argon. "Low oxygen in the chamber is the safest pest-killing technique," he says. But the method is expensive, especially in humid countries where the higher water content in the atmosphere allows pests to survive for longer without oxygen.
Another approach Daniel and colleagues are investigating is to "cook" the pests. They found that to kill all the usual suspects, an artefact must be heated to 52C and kept at that temperature for about six hours. This can be achieved simply by placing the infested object in a black plastic bag, inside a clear plastic bag, and leaving it in the sun.
This low-tech approach is ideal for use in developing countries. But heat treatment has a drawback: the expansion and contraction caused by changes in temperature and humidity can damage the artefact.
Then, you need to keep the bugs at bay once an item has been treated. "Some methods may work temporarily, but the chances of reinfestation are much higher in the tropics," Ramirez says. "And many countries in the tropics do not have the means for artificial climate control." This has left some conservators looking for alternative, non-toxic methods. One solution is biological control.
The approach was hotly debated in November at a symposium hosted by UNU-Biolac and attended by more than 100 delegates from Latin America, Europe and the United States. "Fighting biological agents with other biological entities, like bacteria, fungi, other insects and animals, could be interesting as a 'clean' control method," says Benoît de Tapol from the National Art Museum of Catalonia in Barcelona, who was among those who attended the meeting.
José Ramirez's trial on the Immaculada will involve inoculating the sculpture with Bacillus thuringiensis, a bacterium that produces a toxin. He hopes this will not only kill the beetles, but form spores that stay in the statue, vaccinating it against further attack.
This is an edited version of an article that first appeared in 'New Scientist'
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