Washington: An obscure fungus in the gut of Asian longhorned beetles, which helps the insect munch through the hardest of woods, could help develop methods to control the pest and break down biomass for biofuel, according to a study.

Microbes in insect gut are known to break down cellulose, but little is known about how, or whether, insects degrade lignin. This natural polymer helps plants stay upright and protects them from most forms of microbial attack.

"Lignin is nature's plastic and any organism that wants to get to the sugars in a plant has to be able to get past this protective barrier," said Ming Tien, study co-author and Penn State professor of biochemistry and molecular biology.

"We suspect that the fungus produces enzymes that help the beetles degrade lignin."

Before this report, it was thought that insects are unable to extensively break down lignin, and that they get around the problem either by feasting on wood that has already degraded, or by living close to fungi that can degrade the wood for them.

The beetle is one such insect that attacks healthy trees and bores through the hard wood to get at the succulent energy-rich matter inside. In the process, this invasive pest from China grows nearly 300-fold from being about the size of a grain of rice to a few inches in length.

Kelli Hoover, the study's co-author and Penn State entomologist and her colleagues speculated that the beetle could be harbouring a community of microbes in the gut, which helps in breaking down lignin.

The researchers compared the chemical structure of non-degraded wood before and after it had passed through the gut of two wood-eating insects.

To measure the degree of change in the lignin, they first fed pin oak wood to Asian longhorned beetles. Next they fed ponderosa pine wood to the Pacific dampwood termite, an insect that typically eats only dead wood.

Chemical analyses of faeces from the two bugs indicated that they are able to alter the chemical structure of lignin by selectively adding or removing certain groups of molecules from the polymer. Such alterations, said Geib, make it easier for the insect to break down wood.

However, Scott Geib, a co-author, cautions that while the gut-borne fungus is certainly a key player in degrading wood, it may just be part of a bigger picture.

These findings appeared in the Sunday issue of the Proceedings of the National Academy of Sciences. IANS