The southwestern pine beetle, Dendroctonus barberi, is a native bark beetle that attacks ponderosa pine in West Texas, primarily in the Davis Mountains.
Trees weakened by drought, wildfire, lightning, mechanical damage, or overcrowding are most susceptible to attack. At low population levels, the beetle helps recycle weakened trees as part of a healthy forest ecosystem. During outbreaks, however, it can kill large groups of ponderosa pine.
Adult southwestern pine beetles are small, dark brown to black insects measuring about 2.5 to 4.7 millimeters long. Like other bark beetles, they spend most of their lives beneath the bark of infested trees, where they lay eggs and their larvae feed on the tree’s inner bark.
In Texas, they are generally active from April through October and typically produce three generations each year.
Evidence of beetle attacks
Pitch tubes
Small masses of resin mixed with reddish-brown boring dust form around the beetle’s entry holes as the tree attempts to defend itself. Pitch tubes range from creamy white to reddish brown and are often one of the first visible signs of attack.
Frass
Fine reddish-brown boring dust, or frass, may collect in bark crevices or around the base of the tree. Trees under severe drought stress may produce little resin, making frass the only visible evidence of infestation.
Fading needles
Following a successful attack, needles gradually fade from green to yellow before turning red or reddish-brown. Once the needles have turned red, the tree is considered dead.
Galleries
Beneath the bark, adults and larvae create winding galleries that disrupt the movement of water and nutrients through the tree. These galleries, along with fungi introduced by the beetles, eventually girdle and kill the tree.
Impact
Southwestern pine beetles primarily attack ponderosa pine forests in the Davis Mountains of West Texas. Trees stressed by drought or other disturbances are most vulnerable to infestation.
Once enough beetles successfully attack a tree, they overwhelm its natural defenses. Needles gradually change from green to yellow and then red before eventually falling. Once the needles turn red, the tree has died and cannot be saved.
Between 2011 and 2016, southwestern pine beetle outbreaks contributed, together with wildfires and drought, to the loss of more than half of the ponderosa pine trees in the Davis Mountains, making the species one of the most significant forest health threats in the region.
Life cycle
Like other bark beetles, southwestern pine beetles spend nearly their entire life cycle beneath the bark of their host tree. Females bore through the bark and lay eggs in galleries within the phloem. After hatching, larvae feed beneath the bark before pupating and emerging as adults to locate new host trees.
In Texas, southwestern pine beetles are generally active from April through October and typically produce three generations each year. The life cycle from egg to adult takes about 50 to 60 days during the warmer months but slows considerably during winter.
Control
Maintaining healthy forests is the best long-term defense against southwestern pine beetles. Thinning overcrowded stands reduces competition for water and nutrients, improving tree vigor and reducing the risk of outbreaks.
For active infestations, removing infested trees before adult beetles emerge may help reduce local beetle populations. Healthy landscape trees can also be protected through proper watering during drought and by avoiding damage to roots and trunks.
Preventative insecticide treatments may be appropriate for individual, high-value trees but are generally not practical for forest stands. Treatments must be applied before beetles attack the tree to be effective.
Researchers are also evaluating semiochemical repellents, including verbenone-based products, for protecting ponderosa pines from infestation.