Facts about Pin- and Shot-Hole Borer Infestation

Pin- and Shot-Hole Borers, Ambrosia Beetles

(Coleoptera: Scolytidae and Platypodidae)

(4) Facts about Pin- and Shot-Hole Borer Infestation

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Facts about Pin- and Shot-Hole Borer Infestation

An infestation with ambrosia beetles can occur either in the natural forest, in plantations or in the log-yard. The attack can start within a few hours of the felling of a tree, increase during the next few days and can last for many weeks. The rate of infestation depends on the type of wood and the moisture content of the wood. Usually light, white wood is more susceptible than heavier, red or brown wood. As long as the tree is green and contains a lot of sap, it can be easily attacked. Once the moisture content decreases below 50%, the timber is unlikely to be infested. Wet climatic conditions or rafting of logs also support the attack, since the wood cannot dry properly. The beetles feeding on green timber attack only where sapwood is present but can penetrate the hardwood, too. In log yards, a few different species of pin- and shot-hole borers attack areas of the log where the bark has been removed. The attack of sawn timber is unusual as long as the moisture content of the lumber is low. Live trees in plantations and natural stands are attacked, if the trees suffer from stress. Several stress factors, like an infestation with other pests, contribute towards an ambrosia beetle attack. Damaged trees injured during commercial thinning or by fire as well as trees stressed by drought are far more susceptible to an infestation. The damage to living trees is normally not fatal, since the holes are closed after a few months.

Apart from the general preventive measures, the following recommendations should be followed to lower the risk of an ambrosia beetle attack:

transport logs immediately after felling to the saw mill for further processing and drying
sprinkle logs with water or a preventive application of insecticide, if logs cannot be converted to lumber immediately
instant seasoning of lumber after cutting
if normal seasoning is not possible, cut timber should undergo dip diffusion or pressure impregnation
carry out tending and thinning properly, so that any damage to the trees is minimised
forest operations should not be carried out during wet weather
do not fell trees that are obviously infested, since the timber is of very poor quality

Pin- and Shot-Hole Borers and the Symptoms of their Attack (reproduced from Roberts, H., 1987)

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