Beetles Get By With A Little Help From Their Friends

Southern pine beetles colonize pine trees and lay eggs in galleries within the tree bark. They line these galleries with spores of a beneficial fungus and a bacterium. Inadvertently, they can also bring along parasitic mites and spores of an antagonistic (competitor) fungus. The antagonist fungus competes to colonize the tree, but carries no nutritional value for the larvae. As the beneficial bacterium spreads, it produces an antibiotic that inhibits growth of the antagonistic fungus.
Southern pine beetles colonize pine trees and lay eggs in galleries within the tree bark. They line these galleries with spores of a beneficial fungus and a bacterium. Inadvertently, they can also bring along parasitic mites and spores of an antagonistic (competitor) fungus. The antagonist fungus competes to colonize the tree, but carries no nutritional value for the larvae. As the beneficial bacterium spreads, it produces an antibiotic that inhibits growth of the antagonistic fungus.

Humans living in communities often rely on friends to help get what they need and, according to researchers in the lab of Cameron Currie at the University of Wisconsin-Madison, many microbes, plants and animals benefit from ‘friendly’ associations too.

The Currie team’s study, which was funded by the National Science Foundation (NSF) and published in the Oct. 3, 2008, issue of the journal Science, describes the complex relationship between a beetle, two types of tree fungus and a bacterium that aids in their struggle to survive and thrive.

Research in the Currie lab revealed that adult beetles have a specialized compartment in their bodies used to store two other organisms: a slow-growing beneficial fungus that serves as a food source and a bacterium that produces a unique, newly discovered antibiotic. Interestingly, the antibiotic inhibits the growth of a fast-growing competitor fungus but does not affect the slow-growing beneficial fungus.

Before laying eggs in tree bark, adult female beetles spread the slow-growing, beneficial fungus and bacteria around the area where they will deposit the eggs. The antibiotic from the bacteria prevents growth of the fast-growing competitor fungus but does not harm the slow-growing beneficial fungus, which continues to grow and provide a rich source of nutrition for the developing beetle larvae.

Adult southern pine beetle in flight.
Adult southern pine beetle in flight.

“There are perhaps 10 million species of insects on the planet,” says Currie, an evolutionary biologist. “So, if insects associate with bacteria like this more generally, then there’s potentially a huge number of new places to explore.”

NSF Program Officer Lita Proctor agrees, saying this research, which was co-authored by Jon Clardy of Harvard Medical School, has important implications for the ecosystems these species occupy.

“It may be that some organisms evolved symbioses (cooperative relationships) as a strategy to give them an advantage over others when competing for resources,” said Proctor. “These cooperative relationships may be much more common than we thought.”

In-depth study of these interactions could also lead to identification of new types of antibiotics or other chemicals which may have agricultural or medicinal uses. Thus in the future, we may get by with help from our little friends.

Southern pine beetle larva in a gallery, another name for the place where the beetles lay their eggs. Within the gallery, which is prepared by an adult female, you can see a "lawn" of filamentous microbes. On the left is the fungus found inside the tree bark (red circle). The larva feeds on this fungus. Between the fungus and the larva is another filamentous organism, which is the bacteria (black square).
Southern pine beetle larva in a gallery, another name for the place where the beetles lay their eggs. Within the gallery, which is prepared by an adult female, you can see a "lawn" of filamentous microbes. On the left is the fungus found inside the tree bark (red circle). The larva feeds on this fungus. Between the fungus and the larva is another filamentous organism, which is the bacteria (black square).

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