Bark Beetles– Tiny Adversaries that Cannot Be Ignored
Written by: Tony Arnoldi, Board-Certified Master Arborist WI-0102B
Instead of concentrating only on the most important Ips bark beetle, I thought it might be useful to consider all the major types to see how they work, why they are a concern, and how we can deal with them.
All Bark Beetles are small as adults – they generally are between 1/8th and 1/3rd of an inch in length, depending on species, but what they lack in size they make up for in numbers. Attack can involve low numbers at first, but pheromones released by the initial wave attract many more in subsequent years. Adults feed by chewing their way into the bark and lay eggs in some of the chambers that are created. The eggs hatch into small larvae that chew deeper into the bark, to under the bark, and can include the first 1 or 2 growth rings of wood, so their accumulating damage is shallow. But if many larvae are present, the combined injury begins to interrupt the sap flow to areas beyond (distal to) the damage. The result is withering and dieback of the affected branches and limbs. If the main trunk is heavily infested decline and dieback can involve the entire tree and lead to its death. The larvae finish their feeding and change into the pupal or resting stage for the winter. In the spring the adults emerge, leaving behind many small, scattered exit holes, only 1 to 2 millimeters in diameter – roughly the diameter of a pencil lead.
As mentioned, Ips (or Pine Engraver) Beetles are the biggest bark beetle problem in our area. They can attack both pines and spruces, although pines are favored. (A similar bark beetle attack arborvitaes). They generally need their host to be stressed or weakened for their attack to be successful. Different species of Ips favor different heights or portions of the trunk to attack. Drought, such as the winter of 2021-2022 and extending through most of last year, has weakened many conifers and enabled Ips to spread and increase its attack.
Turpentine Beetles are similar to Ips and often attack conifers concurrently. Their attack is at the base of the trunk, where pitch mases or pitch tubes give away their presence.
Elm Bark Beetles are also in this class and are the main vectors of Dutch Elm Disease. But their boring damage is significant in its own right and controlling them, even on trees receiving care for the Dutch Elm Disease fungus, is a benefit.
The Shothole Borer is a pest of Apples and other fruit trees. They tend to attack older or otherwise weak or “unthrifty” trees. They can cause branch loss, or finish-off declining trees and are often treated to reduce their numbers.
Although all this information can sound depressing, the key is knowing what trees you have, what their level of health and vigor are, and if their locations match their growth requirements. It is usually when there is some mismatch or when some stress or damage comes into play that problems can begin. Most trees that have grown to a significant size have done so because their growth requirements are being met. However, nature does throw some “curve balls” (the recent snowstorm being one example) and that is why arboriculture has exploded across the country and around the world. When needed, trunk spray programs directed at the egg-laying adults have proven very effective. Systemic insecticides are employed as an alternative to, or as a needed supplement to spray programs.
Count on your Wachtel Tree Science Certified Arborist for answers to Bark Beetle or any other insect or disease issue that could come your way. We love having solutions.