Identification and Biology of Southern Pine Bark Beetles

R.C. Thatcher – Program Manager, USDA Forest Service, Southern Forest Experiment Station, Integrated Pest Management Program, and
M.D. Connor – Entomologist, USDA Forest Service, Southern Region, Forest Pest Management.

Integrated Pest Management Handbook, USDA, Forest Service, Agriculture Handbook No. 634, March 1985.

In 1980, the Forest Service and the Cooperative State Research Service of the U.S. Department of Agriculture initiated the Integrated Pest Management Research, Development, and Applications Program for Bark Beetles of Southern Pines. This research/applications effort concentrates on pine bark beetles and associated tree disease in the South. This is one in a series of Integrated Pest Management handbooks.

Life Cycles and Behavior

Southern Pine Beetle
Female beetles initiate attacks on susceptible pines and produce a chemical attractant which attracts other beetles to the same trees. Mass attacks by beetles from the same or nearby infestations follow. Attacks occur first on the mid-stem, then above and below this area. Typically, there are 30-35 attacks per square foot of bark. When a tree has been fully occupied by the southern pine beetle and associated bark beetles, attacks switch or shift to nearby pines, leading to spot growth or spread. "Healthy" pines located around the periphery of large infestations may be killed as the process of beetle emergence and attack continues.

After mating, each pair of beetles constructs a winding gallery in the inner bark, and the female deposits eggs in individual niches cut into each side of the gallery. The galleries, which frequently meet or cross one another, girdle the tree. A blue-stain fungus, carried on the bodies of attacking beetles or associated mites, is introduced to the inner bark-outer wood surface, penetrates the wood in pie-shaped wedges, and plugs up the water conducting system of the tree (Fig. 9). When all eggs have been deposited, most of the parent adults reemerge and attack other trees.

Figure 9 – Blue stain wedges in a southern pine beetle- or Ips-killed tree.

After the eggs have hatched, the young larvae tunnel out and feed on the soft inner bark. Older larvae mine out into the corky outer bark. Pupation takes place in an oval feeding area at the end of each larval mine. Young adults are formed in each of these cells.

Young adults chew individual exit holes through the bark, then fly to nearby newly attacked trees or disperse into the surrounding forest and initiate new infestations. Spot growth is dependent upon the availability of emerging parent and brood adults, the presence of newly attacked and attractive trees, and close proximity to additional suitable host material.

Under ideal condition, beetle development from egg deposition to adult emergence can take place in as little as 30 to 40 days. The number of beetles may increase tenfold in a single generation and, in the deep South, up to seven overlapping generations may develop in a single year. Thus, it is possible for sparse populations to increase to outbreak numbers within a given growing season.

Ips Engraver Beetles
Male Ips beetles initiate attacks on weakened standing trees or on recently cut host material. As with the southern pine beetle, a chemical attractant is released, which leads to mass attack. The males construct small, irregular nuptial chambers in the inner bark where each is joined by one to six females. Each female constructs an individual egg gallery that radiates vertically from the central chamber to form the typical I-, Y-, or H-shaped patterns mentioned earlier. Eggs are deposited in individual niches cut into one or both sides of the galleries. As with the southern pine beetle, the egg galleries and larval mines girdle the tree, while the blue-stain fungus associated with the beetles penetrates and plugs the water-conducting system of the tree.

During warm weather, the eggs hatch in a few days and the larvae make individual mines in the inner bark. When fully grown, the larvae pupate in individual cells or chambers at the end of their mines. Unlike the southern pine beetle, Ips beetles complete their development in the inner bark. Brood adults feed for a time beneath the bark before exiting; several may exit through the same hole. Emerging adults then disperse to weakened, damaged, or dying pines or recently felled trees and logging debris. Population buildup depends largely on drought, stand disturbances, and proximity to other bark beetle infestations.

Depending on the species and environmental conditions, Ips populations can complete their development from egg deposition to adult emergence in as little as 18 to 25 days. All Ips species appear to tolerate higher temperatures better than the southern pine beetle. Thus they thrive under hot, dry, summer conditions, and localized outbreaks can develop within a short time. In the deep South, the small southern pine engraver can pass through as many as 12 overlapping generations in a single season, while the two larger Ips have up to seven overlapping generations.

Black Turpentine Beetle
Initial black turpentine beetle attacks are usually confined to freshly cut stumps and the lower 18 inches of the main trunk. Attacks on individual trees may continue for up to 1 year, eventually extending from the base of larger lateral roots 10 feet or more up the trunk.

Each egg gallery is constructed in the inner bark by a pair of adults. The gallery extends upward for a short distance, then abruptly turns downward for 6 to 20 inches or more. Clusters of eggs are deposited in one or several widened areas or elongated grooves on either or both sides of the gallery. The eggs hatch and the larvae feed side by side away from the gallery, killing as much as a square foot of inner bark.

When feeding is complete, pupal cells are constructed between the bark and wood or within the corky bark in the area previously consumed by younger larvae.

Brood adults feed beneath the bark, and when mature, bore through the bark. They attack the basal stem or larger roots of the trees from which they emerge or fly to fresh stumps or trees damaged by logging, fire, naval stores operations, stressed by drought, or attacked by other bark beetles. Populations of the black turpentine beetle may build up following outbreaks of other bark beetles or extensive stand disturbance. It is not uncommon for the beetle to attack the largest diameter residual trees in the stand.

In the Gulf States, a generation may be completed in 2-1/2 to 4 months. The insect may pass through three overlapping generations each year.

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