Lifecycle of Colorado Douglas-fir beetle

The adult Douglas-fir beetle (Dendroctonus pseudotsugae) is only about the size of a match head but when conditions are right for their population to grow, they are a major threat to Douglas-fir trees.

The adult Colorado Douglas-fir beetle is about the size of a match head, cylindrically-shaped, about 1/4 inch long and is mostly black with reddish wings. The larvae hatch from tiny eggs and can sometimes grow to full size before they pupate (transform to adults). Both adults and larvae feed on Douglas-firs, but prefer trees that are compromised by fire scorch, defoliation, extreme wind damage or root disease.
Unless an irresistible felled tree is nearby, the Douglas-fir beetle rarely moves far from home. A female, who probably was herself born in the tree she calls home, bores under the bark in the phloem layer, laying what are called galleries of eggs as she moves upward. Over the next one to three weeks, the eggs hatch and larvae feed off the tree as they grow to maturity. These young adults and some larvae winter over and start the cycle again in the spring. A mild winter means more adults survive to create an increased population in the spring. Beetle usually emerge mid to late spring, when temperature reaches 60 degrees. Some Colorado Douglas-fir beetle can reemerge later in the season from late June to August.
Fortunately, Douglas-fir beetles are messy insects and they leave telltale signs of their presence. A section of bark can be removed to determine if egg galleries exist, identified by vertical lines in alternating rows. Additionally, a reddish-orange dust is created as adults bore through the bark. Tree foliage looses its color several months to a year later.
If you suspect an infestation on your property and would like to confirm the presence of Douglas-fir beetles, contact SprayTech, Colorado commercial and residential tree-spraying specialists, at 720-248-0000.