Stages of Beetle Attack During The Summer

A Field Guide for Ground Checking Southern Pine Beetle Spots

Southern Pine Beetle Handbook

United States Department of Agriculture Combined Forest Pest Research and Development Program - Agriculture Handbook No. 558 - Issued November 1979

Stage 1 – Pines with Fresh Attacks

SPB attack sequences and development time are more predictable from May to October, and the appearance of beetle – killed pines change 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 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 trees. 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, 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: Foliage . . . appears normal (green) Pitch tubes . . . are soft and white or light pink and usually sticky to the touch (fig. 6). SPB normally attack first at heights of 10-20 feet above ground. So, if there are no pitch tubes visible at eye level, look higher on the trunk. In severely stressed pines, pitch tubes may not appear. Instead, reddish boring dust appears in bark crevices, on the leaves of shrubs, and in spider webs at the base of the tree. Checkered beetles (clerids) . . . may be seen crawling on the trunks of freshly attacked pines (fig. 8). They are common predators of SPB and respond to SPB attractant. Bark . . . remains tight and hard to remove Color of wood surface . . . is white like that of unattacked trees, except close to new adult galleries, where it is brown.
		Figure 6. Fresh pitch tube and SPB adult on stage 1 tree.

		Figure 7. Boring dust in spider webs at base of stage 1 tree.

Figure 8. Adult checkered beetles on stage 1 tree.	Figure 9. Discolored wood of stage 1 tree SPB adult gallery.


Figure 10. Shaved bark with SPB larvae and pupae in outer bark of stage 2 trees.		Figure 11. Ambrosia beetle dust at base of stage 2 tree.

Stage 2- Pines with developing SPB Broods

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 axe or machete (fig. 10). Other features of trees with developing brood are: Foliage . . . is green on most trees containing larvae, but may fade to yellow or turn red before the new generation of beetles emerges from the tree. Foliage color varies greatly by season and among individual trees, so it is not always good indicator for this stage. Pitch Tubes . . . are white and hardened, resembling popcorn (fig. 3). Exit holes . . . may appear at this stage and mark where parent beetles have left the tree. They are round holes about the size of a pencil lead. Ambrosia beetle dust . . . is white and begins to appear in small to moderate amounts around the base of the tree (fig. 11). It is not present in stage 1 trees Bark . . . is loose and easy to peel away from the trunk. Color of wood surface . . . is light brown (fig. 12). It may shade into dark brown with blue or black sections infested by staining fungi. Checkered Beetle larvae . . . show up in SPB galleries in the bark. The larvae are pink or reddish and about ½ inch long (fig. 13).
	Figure 12. Brown wood associated with bark beetle mining in stage 2 tree.

	Figure 13. Checkered beetle larvae in inner bark stage 2 tree.

Figure 14. Ambrosia beetle dust at base of stage 3 tree.
	Figure 15. SPB pitch tubes and exit holes through bark of stage 3 tree.

Stage 3 – Pines Killed and Vacated by SPB

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:

Foliage . . . of most trees is red and needles may have started dropping.
Ambrosia beetle dust . . . is abundant at the base of the tree and is now off white or cream colored (fig. 14).
Pitch tubes . . . are hard and yellow, crumbling easily in your fingers (fig. 15).
Exit holes . . . are numerous (fig. 15).
Bark . . . is very loose and easily removed.
Colored of wood surface . . . is dark brown to with SPB galleries often obscured by the coarse, fibrous borings of sawyer beetle larvae (fig. 16).
Checkered beetle larvae or pupae . . . are purple and occur in pockets within the outer bark shortly after the SPB brood leaves.

Figure 16. Wood discoloration caused
by insect and fungal activity in stage 3 tree.

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