Red Turpentine Beetle (Dendroctonus valens)
The red turpentine beetle (RTB) is a member of the bark beetle family found in pine forests throughout Nevada. It attacks all species of pines in the state, though is rarely a significant pest of any of them. The more commonly
affected native pine species in Nevada are ponderosa, Jeffrey, sugar, lodgepole and western white pines. RTB typically attack stressed or dying trees, as well as freshly cut logs and stumps. However, its attacks are rarely fatal, though it can further weaken trees predisposing them to attacks by other bark beetles.
Description and Biology
The adult beetle has a distinctive reddish-brown color and is ¼ to ½ inches long (Fig. 1), making it the largest of the bark beetles. The adults attack
trees through the warm season and generally peak by mid-summer. The female beetle bores through the bark and is soon joined by a male with whom she breeds. The beetles then chew a ½ to 1 inch wide tunnel (called an egg gallery) between the bark and wood. The gallery normally extends down from the entrance hole and is filled with boring dust (frass). The female lays groups of eggs, up to 100, along the sides of the gallery.
The eggs hatch in from one to three weeks into white larvae with brown heads and a brown area on the hind end. The larvae then tunnel in groups away from the egg gallery. The group feeding characteristic of RTB larvae is unique and produces chambers in the inner bark of 0.1 to one square foot in area (Fig. 2), rather than the individual larval tunnels like most other beetles.
After two or more months the larvae transform into pupae. They remain in this stage for another week or so as they turn into adult beetles. The beetles then bore out through the bark, leaving small round exit holes, and fly to other trees to begin another generation. The beetles normally produce one generation per year, but may produce more or less depending on the climate. They spend the winter under the bark in either the adult or larval stage.
Evidence of Attack
The most obvious sign of RTB attack is large (up to 2 inches across) reddish globules of pitch (pitch tubes) at the point of entry (Fig. 3). These are located on the lower part of the tree trunk and on the root crown. Very weak trees may not produce much pitch in response to
the beetle attack and pitch tubes may be missing. However, accumulations of reddish-brown boring dust will be present at the base of the tree and in bark crevices. Piles of coarse, granular pitch are often present with the boring dust
Internal evidence is the distinctive gallery patterns left by the feeding larvae. The beetles also introduce the blue stain fungus into the tree. The fungus grows in the live wood tissue clogging the water transporting vessels and staining the wood blue. The fungus may also reduce the flow of pitch, reducing the trees protective mechanism.
Prevention and Control
As mentioned above, it is stressed and weakened trees that are most often successfully attacked by RTB. Therefore, practices which maintain healthy, vigorous trees are the best way to prevent RTB problems. Trees growing close together compete for water, sunlight, and growing space, causing stress to the trees. Thinning the trees will provide more of the necessary resources for the remaining trees. Thin during periods of good precipitation and use the “diameter plus ½” rule as a spacing guide. That is, the distance, in feet, between adjacent trees should be equal to 1½ times the tree diameter in inches. Retain upright, undamaged, full crowned trees.
During periods of drought, give trees a good, deep watering monthly. Trees injured or weakened by activities like home construction, road building, land clearing and logging are commonly attacked. Prevent direct injury to tree stems and roots during these activities by flagging protective zones around individual or groups of trees. Avoid activities that compact soils over tree roots.
Individual trees can be protected by applying a pesticide to the trunk before the beetles attack. Spray the bottom six to eight feet of trunk. Be sure the pesticide is registered for use against bark beetles on pine, and apply it only as directed by the label. Call the Nevada Division of Agriculture for a list of pesticides registered for use on rtb. read, understand, and follow instructions on pesticide labels.
Watch freshly cut pine logs and firewood carefully for signs of infestation. Remove the infested wood from the site or kill the beetles before they emerge. Logs can be chipped, burned or cut into firewood. Firewood should be placed in a sunny location and covered with thick (= 3 mil), clear plastic. Be sure all edges are buried which will bake the beetles under the bark. Leave pile covered for three months during hot weather, and longer at other times of the year. Peel the bark off freshly cut stumps to prevent beetles from infesting them.
Authored by: John Christopherson- Resource Management Officer- Nevada Division of Forestry
- Contact Information
Forest Health Specialist
2478 Fairview Drive
Carson City, Nevada 89701