by Ronald F. Billings and Herbert A. Pase III
Online format prepared by Quintin C. McClellan ~ Department of Entomology ~ VPI & SU ~ Blacksburg, VA ~ USA
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Locating SPB Spots From Ground Level
How to Identify SPB Attacks
Other Bark Beetles
Seasonal Variation in Attack Symptoms
Stages of Beetle Attack During the Summer
Collecting Spot Expansion Data
Using the Control Priority Guide
The Buffer Strip
A Word on Control Priorities
The job of locating and controlling the southern pine beetle (SPB) takes the teamwork of three separate field operations aerial survey, ground check, and direct control. Aerial surveys locate many areas with dead or dying pines believed to harbor SPB. Some are active beetle spots; others are not. Only by checking from the ground can we be sure. So, on the basis of tree symptoms visible from the air, aerial survey crews assign each spot a high, medium, or low priority for ground checking. Ground check crews then visit newly detected spots, giving first attention to high priority areas. Your responsibility, as a member of the ground check crew, is to see firsthand the extent of beetle activity in each spot and to determine if further tree killing is likely to occur. This handbook shows how to recognize various stages of SPB attack, how to decide if control is needed, and how to mark buffer strips for control crews.
To find newly detected spots, use a map and compass, if necessary, to arrive at the general area indicated by the aerial survey team. Once there, look for a group of yellow- or red-topped pines (fig.1). Spots that cannot be found after a reasonable search should be rechecked during the next aerial survey flight. The aerial crew may be able to correct errors in plotting or to pinpoint landmarks guiding you to the spot.
Like any living thing, pines may die from a variety of causes. But how can you tell if they were killed by SPB? The best way is to remove sections of bark from trees with fading (yellow) foliage or from trees with bark just starting to loosen. Look for the winding, S-shaped tunnels or galleries made only by SPB adults (fig. 2). SPB galleries are filled with a sawdust-like material (frass) left behind by feeding adult beetles.
In pines just coming under attack, galleries are not yet present. The first symptom of SPB in this case will usually be pitch tubes in bark crevices. These glossy masses of resin mark where the adult beetles bore into the trunk of a tree. SPB pitch tubes are soft and pink when fresh, becoming hard and white or yellow with age (fig.3). But remember, pitch tubes alone are not reliable indicators of SPB attack because other bark beetles also leave them.
For a couple of weeks after attack, you may find SPB adults within the S-shaped galleries where they lay eggs. The SPB itself is surprisingly small, considering the amount of damage it can do. The adult beetle measures only 1/8 of an inch long and is black or dark brown. Because of their small size, you may have difficulty recognizing SPB adults among the many other bark-inhabiting insects. Again, the S-shaped galleries provide telltale evidence that SPB killed the tree, even when the beetles themselves are no longer present.
The southern pine beetle is not the only destructive bark beetle in the South. Other beetles, including Ips beetles and the black turpentine beetle (BTB), also kill pines, but usually in small, scattered outbreaks not requiring control. This means that you must be able to tell the difference between SPB attacks and those of other bark beetles. Identification can be difficult because the various beetles are similar in many ways.
Yet there are unmistakable differences. For instance, the black turpentine beetle is about 1/4 of an inch long, which makes it much larger than the southern pine beetle. Also, the BTB normally limits its attacks to the lower 10 feet of the trunk, while the SPB attacks at almost any height on the tree. Pitch tubes of the BTB usually are reddish and much larger than those of the SPB (fig.4). The black turpentine beetle's galleries follow no distinct pattern.
Differences between SPB and Ips beetles are less obvious because the insects are similar in size. Adult galleries provide the best clue for recognizing Ips attacks. They are long, straight tunnels often joining to form a Y or H shape. Ips galleries usually are not packed with frass (fig.5). Keep in mind that Ips and black turpentine beetles may occur in the same tree as the southern pine beetle.
The time it takes SPB to grow from eggs to adults varies seasonally, as does the time it takes for symptoms of beetle attack to appear in infested pines. Judging the presence or absence of SPB and the stage of development during the winter months can be a difficult task. Foliage on trees attacked in cold months may remain green for long periods, although such trees quickly lose their needles once foliage discoloration begins. Because the beetle needs 2-4 months to mature during cold months, some winter killed pines with bare crowns may still contain SPB. Also, the insects in winter often re-attack the top and base of a tree already containing developing broods. This leaves different beetle life stages at different heights in the same tree. Because of these difficulties, no attempt has been made to categorize infested spots for the winter months.
SPB attack sequence and developmental time are more predictable from May to October, and the appearance of beetle-killed pines changes with a distinct pattern. On the basis of these facts, three categories for beetle-infested pines have been established, reflecting various stages of attack. The number of trees in each stage of attack and where the trees are located in a spot is the key to whether a SPB spot is likely to spread in warm weather. It is essential, then, that you learn to recognize these three stages to correctly determine the need for control.
When SPB bore into a tree, they produce chemicals attracting other beetles to the tree. This sets off a chain reaction. The attractants usually bring together more than enough beetles to kill the pine, and excess beetles spread to nearby trees. They, too, give off the attractant, which calls in still more SPB. The infestation grows. Because only freshly attacked trees are sources of attractant, it is important to identify their number and location. Only then can you determine if the spot is likely to spread. The following characteristics identify trees with fresh attacks:
Soon after adult beetles have overcome a tree, they stop producing attractant. Eggs hatch , and small, white SPB larvae start feeding in inner bark mines, which are mixed among the S-shaped adult galleries (fig. 2). As larvae develop, they move into the outer bark, where they eventually change into white pupae and then into brown or black adults. It is important to realize that the beetle has these various forms. To see the later beetle stages, carefully shave away outer layer of bark with an ax or machete (fig. 10). Other features of trees with developing brood are:
After maturing in the bark, new adult beetles bore their way out and fly off to attack another pine. A tree is termed "inactive" when no SPB of any stage can be found in it. Other features of inactive trees include:
Is the new spot you have located a threat to grow larger? It may well be. The southern pine beetle can readily spread if it has three conditions: Attractants from stage 1 trees, continuous emergence of attacking adult beetles from stage 1 and stage 2 trees, and pines to attack (fig. 17). During the summer, spots with no stage 1 trees are not likely to expand because attractants are no longer present. And spots with only stage 3 trees-since beetles have already left-need no control at all. The following steps, to be used between May and October, explain how to collect information for use in the control priority guide:
To assign a control priority using information gathered at the spot, use table 1. Four keys to spot growth (A, B, C, and D) appear in the left hand column. for each of these, select from the middle column the classification matching your spot. Select from the right-hand column the risk-rating points for the classification. Take one number for each key and add them together. This gives you the total risk-rating points for your spot.Table 1. Guide to southern pine beetle spot growth and control priorities (May through October).
|Key to Spot Growth||Your spot's classification||Risk-rating points1|
|Number of freshly attacked trees and those with developing brood||1-10
more than 50
|Pine basal area (or stand density) at active head(s) (ft2/acre)||less than 80 (low density)
80-120 (medium density)
more than 120 (high density)
|Average size class of timber (in inches)||pulpwood (9 in or less)
sawtimber (more than 9 in)
No matter which means of control is used, success hinges upon treating all stage 1 trees. The best insurance is to cut a buffer strip of uninfested pines around the active head of a spreading spot. This tactic interrupts the beetles' flow of attractants and stops their advance. The buffer strip also provides a margin of error, just in case attacked pines were initially overlooked or the spot has expanded since then.
A buffer strip 10-40 feet wide is enough for medium and low priority spots and for high priority spots with fewer than 30 trees. But a buffer strip 40-100 feet wide is needed for large high priority spots (fig. 18). As a rule of thumb, the number of trees in the buffer strip should not be more than the combined number of stage 1 and stage 2 pines in the spot being treated. The buffer strip should enclose all stage 1 and stage 2 trees and be widest in the direction that the spot is expanding.
If control is planned within 2 weeks after the ground check, mark the buffer strip at the time of the first ground check. If control is not planned this soon, wait until just before the control date to mark the buffer strip or carefully recheck its boundaries before treatment. Otherwise, the spot may enlarge beyond the buffer zone before the control starts.
Effective control requires prompt removal of the buffer strip and stage 1 trees. For large spots, this should be done first, then you can remove the other infested trees in the spot. Salvaging stage 3 trees is not critical to control, but can be done later.
Decisions on controlling SPB spots depend not only on the control priority, but also on the availability of crews and equipment, access to the spot, and market value of beetle-killed pine. If possible, high priority spots should be controlled promptly or they will spread, while medium priority spots can be handled as time permits. A low priority spot may need no control. Since it is uncertain what will happen in medium or low priority spots, you should recheck them every 4-6 weeks until they are controlled or become inactive. During major SPB outbreaks, aerial surveys are the most practical way to monitor uncontrolled spots after the first ground check.
southern pine beetle...Dendroctonus frontalis, a bark beetle identified by the S-shaped galleries it makes beneath the bark of attacked pines
spot...A group of dead or dying trees infested by the southern pine beetle
spot growth...The natural expansion of untreated spots as additional live trees on the outer edge of a spot become infested.
stage 1 pine...Infested pine showing symptoms of fresh attacks by SPB.
stage 2 pine...Infested pine with developing broods (larvae, pupae, or new adults) of SPB.
stage 3 pine...Pine killed by SPB from which all broods have emerged.
spot growth...The natural expansion of untreated spots as additional live trees on the outer edge of a spot become infested.
active spot...SPB infestation in which one or more of the attacked trees contain beetles or brood.
inactive spot...SPB infestation in which the beetle in all of the attacked trees have completed development and emerged.
active head of spot...That portion of a SPB spot containing beetles in the process of attacking live trees.
buffer strip...A group of live uninfested pines, adjacent to the most recently infested trees in a spot, that is felled to assure effective control.
Ips beetles...A group of related pine-killing beetles that can be distinguished from SPB by the unfilled Y- or H-shaped galleries made by attacking parent beetles.
black turpentine beetle...Dendroctonus terebrans, a large bark beetle commonly found attacking the lower trunks of pines, producing large reddish pitch tubes.
The guidelines for setting control priorities on SPB spots resulted from research conducted by the Texas Forest Service (TFS). The photographs were provided by the TFS Forest Pest Control Section.
The authors appreciate the manuscript reviews and other assistance given by state pest management specialists throughout the South and by Forest Health Protection, State and Private Forestry, Region 8, Forest Service, U.S. Department of Agriculture.