Jeffrey Pine Beetle (Dendroctonus jeffreyi)
The Jeffrey pine beetle (JPB), a bark beetle, is the most serious insect pest of Jeffrey pine. The beetle attacks only Jeffrey pine and occurs in the Sierra Nevada wherever this tree species is present.
The beetle is typically present in relatively low numbers (endemic) in any given area, and breeds in single slow growing trees of reduced vigor. In this respect it serves an important ecological function by helping recycle
older trees and allowing newer, vigorous ones to follow. However, forest conditions occur periodically which are favorable for the JPB, and its population increases to epidemic levels and causes widespread group kills of Jeffrey pine trees.
As with other bark beetles, the JPB spends most of its life under the trees bark in any of four stages: eggs, larvae, pupae, or adults. The adult beetles are black or dark brown colored and are one of the larger in this genus, about five-sixteenths of an inch long (fig. 1). They emerge from infested trees as early as April in warm years and attack live trees. Females colonize green trees first, producing a chemical odor (pheromone) which attracts males and other males to the tree. As males arrive they also produce pheromone attractants that contribute to a mass attack. The adults bore through the bark to the wood/bark interface
and excavate a vertical gallery along which they lay their eggs. The gallery is packed solidly with boring dust and excrement called frass as the eggs are laid. The eggs incubate for 1-3 weeks before hatching into curved, white legless larvae with a yellow head. The larvae then bore away from the egg gallery across the grain of the wood, feeding on the inner bark (phloem) and cambium. The insect can overwinter as larvae, or transform into pupae in chambers excavated at the end of their galleries. From the pupal stage, they become adult beetles in about 10 days. The adults then tunnel out through the bark and seek out new trees to attack. Depending on the climate, the beetles can have up to two generations per year, although one complete and a partial second generation is more typical.
The adults transport a fungus on their body into the host tree which stains the wood a bluish-gray color as it grows. The fungus clogs the trees vascular system and restricts the flow of water and nutrients within the tree. The clogged transport system combined with the larval and adult feeding in the phloem and cambium cause the trees death.
Evidence of Attack
Large reddish globules of pitch along the middle and lower tree trunk are usually the first signs of an attack. These pitch tubes are the result of the tree trying to “pitch out” the beetles. If the beetle was pitched out, the globules are clear and the dead beetle may be evident in the pitch. If the beetle successfully attacks the tree, the pitch tubes are filled with reddish boring dust. Not all trees will produce tubes;
very weak trees are often unable to produce pitch. In this case, boring dust will be present in bark crevices and cob webs below the entrances holes and at the base of the tree. The trees foliage begins to change color as it dies. Beginning at the top and gradually extending downward, normally green needles turn yellow, and finally reddish-brown. By the time the foliage turns reddish-brown, the tree is dead and the beetles have usually left. The beetle leaves a distinctive gallery pattern underneath the bark (fig. 3) which is packed with frass. No other insects breeding in Jeffrey pine make a gallery with this shape.
The best strategy for preventing JPB problems is to keep trees healthy. Thinning the trees to provide sufficient growing space is an important practice. Tree spacing should follow the diameter plus ½ guideline. That is, the distance, in feet, between adjacent trees should be equal to 1Â½ times the tree trunk diameter in inches. Retain upright, undamaged, full crowned trees. Watering trees during drought periods will also help keep them healthy and vigorous.
Individual high value trees can be protected with an annual application of insecticide. The insecticide must be applied before adult beetles attack the tree, by early April. Trees killed by beetles the previous year may still have green foliage the following spring when spraying is done. Look for pitch tubes, boring dust and other signs infestation before spraying a green tree. Spraying dead trees is expensive and of no value. Contact the Nevada Division of Agriculture for a list of pesticides registered for use against bark beetles on pine. read, understand, and follow instructions on pesticide labels.
Beetle attacked trees should be cut and removed from the forest before the brood matures. If it is impractical to remove the trees, then they can be burned, or the bark can be peeled off which exposes the insects to the weather and predators. If the tree is cut up for firewood, the wood should be piled in direct sunlight and covered with thick (3 mil), clear plastic. The edges of the plastic should be buried underground to trap any emerging beetles. This will raise temperatures under the plastic and bake the insects in the wood. Keep the pile covered for 3 months.
Authored by: John Christopherson- Resource Management Officer- Nevada Division of Forestry
- Contact Information
Forest Health Specialist
2478 Fairview Drive
Carson City, Nevada 89701