For Jeffrey pine beetles, the adult gallery will have a j-shaped hook at the base and then will travel vertically along the trunk for up to three feet. Other species of adult beetles excavate shorter, vertical or even horizontal galleries. After the eggs hatch, the larvae feed on the inner bark and dig out galleries of their own, often perpendicular to the original gallery of the parents. As the larvae feed, their ever-widening galleries, in addition to the adult galleries, will cut the phloem and outer sapwood all the way around the tree, damaging or killing it. This is called girdling.
Some beetles also carry a fungus on their body surface or in special pouches on their body.
The fungus clogs the tree s water conducting ability. The physical damage caused by chewing, together with the action of the fungus, may kill the tree. The larvae feed for several weeks or months before they pupate and transform into adults. The adults chew through the bark of the tree and emerge. Odors released by other beetles cause newly emerged beetles to fly to another tree, attack again and repeat the cycle.