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American Association for the Advancement of Science

No beetle is an island

An adult southern pine beetle.

Ecologically speaking, the southern pine beetle is a well-connected bug. It lives in pine trees and uses a fungus that also inhabits the pine tree as a food source for its larvae.

Scientists have now discovered a few more characters in this story, turning a three-way relationship into a veritable soap opera.

In the original cast of characters, we have the southern pine beetle, Dendroctonus frontalis, which is a major pest in the pine forests of the southern United States. The beetle carries little bits of the fungus Entomocorticium around in a pouch under its head and then deposits some of the fungus in the cavities within the pine tree where it lays its eggs.

The fungi thus get themselves "planted" around the tree and also provide food for the beetle larvae once they hatch.

But, this mutually beneficial relationship is threatened by another type of tree fungus, called Ophiostoma, which can suppress the growth of Entomocorticium. Unfortunately for the beetle, however, this competitor fungus doesn't make a good food source for beetle larvae.

Enter: actinomycetes (a type of bacteria). Jarrod J. Scott of the University of Wisconsin, Madison and colleagues have discovered that this bacterium lives on the southern pine beetle. It also produces a compound that is poisonous to competitor fungus, Ophiostoma. So, the bacterium helps the protect the beetle's food source.

These findings show how many connections exist between different organisms. The authors also say that mutually beneficial relationships between insects and antibiotic-producing bacteria may be more common than we ever knew and may point the way toward new antimicrobial compounds.


The study appears in the 3 October issue of the journal Science.