Texas Cooperative Extension Harris County

Pine Bark Beetles

James V. Robinson
Extension Entomologist, The Texas A&M University System

More pines are killed by bark beetles than by any other group of insects. All common pines in eastern Texas are attacked by the beetles. Although they usually breed in forest trees, pines in urban areas also provide breeding places.

Description of Habits

Five species of bark beetles are responsible for most of the damage to pines: the southern pine beetle (Dendroctonus frontalis Zimm.); the three southern Ips engraver beetles (Ips avulsus Eich., Isp calligraphus Germ. and Ips grandicollis Eich.); and the black turpentine beetle Dendroctonus terebrans Oliv.).

Bark beetles spend most of their lives beneath the bark of host trees where adult beetles chew out tunnels, or galleries. Upon hatching from eggs laid along the gallery sides, the young larvae bore away at right angles. When fully developed, the larvae transform to pupae and then adult beetles. They chew through the bark and fly to attack other trees. The tree's death results from girdling of the cambium layer either by adults forming the egg galleries, by larval feeding or by fungi brought into the tunnels by the attacking beetles.

Southern Pine Beetle

This is the most destructive insect pest of pines in the South. Outbreaks may cover many acres and kill thousands of trees. Pines of all sizes are attacked, and even healthy, vigorous trees are killed by this beetle during epidemics.

All life stages of the Southern pine beetle winter in bark. When adults emerge in the spring, they do not attack healthy, living trees. Instead, they seek out and invade trees attacked but not killed the previous fall. Generally, they attack the middle and upper trunk first, then continue down to within 5 feet or less of the ground. In the southern states, adults emerge in March and may attack the lower trunk first.

The brown or black adult beetle is from 3/32- to 3/16-inch long. its posterior end is convex and rounded in contrast to the concave, truncate and spined posterior end of the Ips beetle. Winding "S" - shaped egg galleries are made by adult beetles beneath the dry outer bark. Larvae are white and legless with glossy, reddish brown heads; their bodies are wrinkled and curved. Under optimum conditions, the entire life cycle may be completed in 30 days and five to seven generations may occur each year.

Ips Engraver Beetle

The three species of engraver beetles are similar in habits and life histories, but can be readily distinguished by their size and the number of projections or teeth on their posterior ends. IPS beetles are attracted to trees weakened or injured by some natural or mancaused injury. Lightning damaged trees are especially attractive to the beetles and often are the center of spread to nearby trees. Normally, Ips beetles attack and kill only one or a few trees in a given spot, but if conditions are satisfactory, hundreds of trees may be killed.

In contrast to the "S"-shaped galleries made by southern pine beetles, adult Ips beetles make either "H"- or "Y"-shaped tunnels. The posterior ends of adult Ips are concave and armed with small spines. Larvae resemble those of the southern pine beetle.

Ips avulsus, smallest of the engravers, is a brown beetle about the size of the southern pine beetle. There are eight spines (four on each side) on its posterior end. It prefers to attack the upper stem and limbs of trees. One generation may be completed in 20 to 30 days, with eight to ten generations occurring each year.

Ips grandicollis is the medium-sized engraver, 1/8- to 3/16-inch long. This brown beetle has five spines at each side of its posterior end and commonly invades the middle and upper trunks of pines. There are four to six generations per year.

Ips calligraphus has six spines at each side of its posterior end, and is the largest of the three beetles - from 3/16- to 1/4-inch long. It tunnels in the lower parts of the main stem. There may be six or more generations per year.

Black Turpentine Beetle

The black turpentine beetle attacks fresh stumps and trees with mechanical or burn injury to the bark, or with roots damaged by machinery or compaction. Attacks are usually limited to the lower 6 to 8 feet of the trunk. Turpentine beetles do not attack a tree in such large numbers as the other bark beetles; therefore, the tree may recover from their attack. Adult beetles construct egg galleries downward from entrance holes. Larvae feed in groups next to the egg galleries, killing large patches of inner bark and forming large fan-shaped or "D"-shaped galleries.

This black beetle is the largest pine bark beetle in the south, and ranges from 1/4- to 3/8-inch in length. The posterior end is convex as in the southern pine beetle. Larvae are large, white and legless. Two generations normally are completed in a year.

Interrelations of Bark Beetles

A tree may be killed by the attacks of a single species of bark beetle. Commonly, however, two or more species attack the same tree. Ips beetles may be attracted to trees initially attacked by southern pine beetles and vice versa. Egg galleries of different bark beetle species may be intermixed in the same section of a host tree.

Signs of Attack

Although the different bark beetle species have different habits and life histories, symptoms exhibited by infested trees are similar for all species.

Bark beetle-injured trees can be difficult to detect at an early stage because the small, yellowish-white or reddish-white masses of resin called "pitch tubes", which mark the points of beetle entry, are often inconspicuous. In fact, during very dry weather, there may be no pitch tubes but only reddish boring dust in the bark crevices.

The foliage of heavily infested trees changes from dark green to light green, yellow, sorrel, and finally reddish brown. These changes usually occur over a period of 1 1/2 to 3 months. During the summer, initial fading may not occur until 3 or 4 weeks after the bark beetles have entered the trees, so that beetle emergence takes place about the time affected trees begin to fade. If trees are infested in late fall, they may remain green all winter and not fade until after insect emergence the following spring.

Positive identification of bark beetle infestations are made by removing a square of bark. Exposed on its inner surface and on the outer surface of the tree are the characteristic gallery patterns of the bark beetles.

It is important that homeowners carefully and frequently inspect pine trees for signs of beetle activity. Be on the alert for any foliage color change as an indication of pine bark beetle activity. But remember that foliage color change in pines is a slow process and may not occur until 3 or 4 weeks after bark beetles have entered the tree, or until the following spring after a fall attack.

Resources

the Texas AgriLife Extension Service - Harris County

the Texas AgriLife Extension Service-Harris County