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Twig Beetle

In Pine Shoot

Tree Infested

With Twig Beetle

Twig Beetle Description

Twig beetles are native to the Southwest and are in two of the largest genera of bark beetles, containing more than 120 species in North America. These tiny beetles are only about 2 mm long (~1/8 in), about half the size of Ips confusus bark beetle. Their coloring is dark, usually reddish to dark brown. Twig beetles are a natural component of the ecosystem that usually attacks but not always kills stressed or damaged trees.   These beetles attack several pines including piñon, ponderosa and Austrian. Outbreaks vary, but population increases may be encouraged by drought. Twig beetles normally attack the tips of branches, typically less than 3" in diameter, causing minor branch dieback, but during periods of drought they are able to move further down the branch.    Thus, they cause mortality by either killing the branches so the tree is unable to support itself or by attacking thin barked portions of the trunk.

Twig beetles have two or more generations per year depending on climate. In the spring, adults emerge from under the bark and fly to a suitable host. The male twig beetle acts as a pioneer beetle that bores into the host tree and releases aggregation pheromones to attract multiple females. The male beetle generally mates with three to five females in a single nuptial chamber. The females then tunnel galleries encompassing the branch with several egg galleries radiating from it. Eggs are placed in niches along the side of the female gallery.              The larvae feed on the cambium of the twig. Under the bark they transition from egg to larva to pupa to adults, as they feed moving away from each other. To overwinter they tunnel down the pith of the twig.     As twig beetles infest a branch or entire tree, they are usually accompanied by Piñon Ips bark beetles. Pinon Ips beetles spread a deadly fungus to trees. The blue stain fungus is carried by the Ips beetle to help overcome a tree’s defenses. This fungus transfers from tree to tree with the bark beetle and works its way into the trunk, cutting off the flow of water-based nutrients. The fungus leaves a blue discoloration within the wood.

Evidence of twig beetles can vary. Single branches or twigs will have needles that fade from green to yellow and then reddish-brown.             To detect the beetle before the needles fade, look for small spots of sap on the branches in combination with a fine sawdust.                              Also, infected branches may have the appearance of being wrinkled or sunken. Unlike trees colonized by the Ips beetle, trees infested with twig beetles have the possibility to survive the attack. Pruning of infested branches can stop twig beettle spread. However, if the majority of the branches are infested, and such pruning will leave little healthy crown remaining, the tree cannot be saved.

Recommended Control

Mallory Landscape and Design recommends the application of Carbaryl at 2% by volume for twig beetle control in spring. The entire crown of the tree will sprayed for protection against these boring insects.                Early prevention is the best way to protect or reduce the chance of tree loss to twig and bark beetles.

New Mexico Pesticide Applicator License #55493

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