Mountain Pine Beetle have a one year life cycle that begins with the flying and infesting of new trees between early July and late September.  A pair of beetles bore into a tree, lay their eggs in galleries under the bark and die in late summer/early fall.  These eggs hatch into larva in late fall and begin feeding inside the tree.  The larva produce an alcohol called glycerol that acts as antifreeze, protecting them during the cold winter months.  The larva feed during the winter and spring months on the tree’s phloem layer, located under the bark of the tree.  The phloem is the tree’s veins that carry water and nutrients up to the top of the tree.  The larvas disturb this flow, effectively girdling and killing the tree.  The larvas pupate in early summer and emerge as adult beetles in midsummer, starting the cycle over.  The beetles are looking for host trees that can provide enough food to last all winter.  These trees are typically greater than five inches in diameter at breast height.  The spread rate from summer to summer during the current epidemic levels can range from 5 to 50 new infestations each year.