Eurasian spruce bark beetles (Ips typographus) burrow into the bark of Norway spruce (Picea abies) trees where they mate and lay their eggs. Major outbreaks in Europe have decimated millions of hectares of conifer forests. The beetles preferentially attack trees that are already infected with symbiotic fungi (such as Grosmannia penicillata), which is thought to weaken host trees and break down their chemical defenses, allowing the beetles to successfully develop in the bark.
Click here for original story, Conifer-killing beetles use smell of beneficial fungus to select host trees
Source: Phys.org