Pine Bark Beetles
Cooperative Extension Service, College of Agricultural and Environmental Sciences, The University of Georgia Bulletin 1097, October 1993, 8 pp.
Ips beetles vary in size by species. Adults are cylindrical in shape, usually dark brown-to-black and range in length from 2 to 7 mm (0.1-0.3 inch). The rear end of Ips beetles are sunken, or "chopped off" in appearance, with four to six spines along each side of the sunken area. (see Figures 6 and 7).
Although this group contains several species, all Ips beetles have the same general appearance and similar habits. Male Ips beetles initiate attack by boring through the bark and constructing mating chambers. From two to four females (depending on species) join each male. These females excavate rough Y, H or I shaped egg galleries in the phloem.
Pitch tubes formed at the point of attack are normally less than 1/2 inch in diameter and look like those associated with SPB attacks. As with the SPB, often the only visible sign of attack on severely weakened trees is the presence of brown boring dust in bark crevices and on spider webs, since pitch tubes may not form.
Egg galleries radiate out from the mating chamber, usually parallel to the grain of the sapwood. Eggs are deposited at regular intervals along the sides of the galleries. The galleries usually groove the sapwood and generally are free of boring dust (Figure 12). Ips beetles complete their life cycle in 25 days or more depending on species and temperature.
|Figure 12. Ips Beetle Galleries and Mating
Chamber. Note Lack of Frass in Galleries
The bark of infested trees can be covered with large numbers of holes bored by emerging beetles. However, serveral newly emerged Ips beetles often emerge from a common exit hole, resulting in far fewer emergence holes in the bark than with SPBs. Emergence hole size varies with the species of Ips.
Once beetles successfully attack trees and constuct egg galleries, the blue-stain fungus they carry has usually been introduced. These trees cannot be saved, even if treated with an insecticide to kill the larvae.
The small southern pine engraver, I. avulsus , is the smallest of the Ips beetles. Adults are 2.3 to 2.8 mm (0.1 inch) long (Figure 6) and have four small spines on each side of the sunken area on their rear ends. I. avulsus breeds in all species of pines. It prefers the thin bark on cut tree limbs and tops, but can attack and kill groups of young, vigorous trees and the tops of large, living trees. Ips avulsus attacks on the tops of large trees and are often associated with attacks by other species of bark beetles on the lower portion of the tree. The life cycle of this beetle can be completed on as few as 25 days, and there may six generations each year.
The eastern fivespined ips, Ips grandicollis, is intermediate in size among the Ips beetles commonly found in Georgia. It ranges from 2.8 to 4.7 mm (0.1-0.2 inch) long (Figure 6). This engraver has five spines on each side of the sunken rear end. It commonly infests the middle portions of the open trunk as well as large limbs in the crowns. Populations normally develop in areas of recent logging operations. The life cycle requires 25 to 30 days, and there may be six generations each year in Georgia.
The sixspined ips, Ips calligraphus, (see Figure 6), is the largest of the southern Ips species. Adults range in length from 3.5 to 6.5 mm (0.15-0.25 inch), with six spines on each side of the sunken area at the rear end. They commonly infest the lower trunks of pines. Trunks, stumps, and large limbs of recently felled trees are favored breeding sites, although they can attack trunks of apparently healthy trees.
This is often the first species of bark beetles to attack drought-stressed trees. It also frequently attacks trees damaged as a result of "hot burns". Attack on living trees usually occur on the lower portions of trees greater than 15 cm in diameter. Egg galleries, usually three to five, radiate from a central mating chamber and run up and down, grooving both the bark and the wood. The life cycle may be completed in 25 days, with six or more generations per year.
The pine engraver, Ips pini, only occurs in north Georgia, where it usually attacks eastern white pines. Adults are brown to black, from 3.5 to 4.5 mm (0.14-0.2 inch) long and have four teeth on each side of the declivity (not pictured). Egg galleries, from three to six, radiate away from the nuptial chamber, deeply scarring the sapwood.
Ips beetles and BTB are present throughout Georgia virtually every year but seldom kill large numbers of trees in one spot. However, under certain conditions, both the SPB and Ips beetles can reach outbreak levels and cause widespread damage.
Of the bark beetles in Georgia, the SPB is the most damaging and most subject to wide-area outbreaks. It is common for more than one species of bark beetles to infest individual trees, especially in beetle outbreaks. A large number of other insects are also associated with bark beetle attacks and/or dead and dying pine trees.
Proper identification must be made of all suspect bark beetles. If you are unsure of your beetle identiftication, take bark and beetle samples to your local county Extension or Forestry Commission office for identification.