Ips beetles

Ips beetles are one group of bark beetles. Adults are small reddish-brown to black beetles about 1/8 to 3/8 inch (0.32 to 0.95 cm) long and have a pronounced cavity on the rear end that is lined with three to six spines. Larvae are whitish to pale yellow and about a half inch long when mature. Larvae are 1/4 inch (0.66 cm) long at maturity, are white to dirty grey and have dark heads (Figure 1).

Biology

Adults breed in dead trees and cut wood. They overwinter under the bark or in the litter below trees and attack weakened tree in the spring. Males first create a cavity under the bark referred to as the nuptial chamber. Females are attracted to the males by pheromones. Males usually mate with three females who will create egg laying galleries off the main tunnel created by the male. These tunnels will produce either a “Y” or an “H” shape (Figure 2). Females will lay eggs along these cavities. After eggs hatch the larvae begin to tunnel in lateral galleries that lightly etch the sapwood. There can be two to four generations a year.

Damage

Larvae feeding below the bark cause part of the tree to die. This could be one branch or the whole top portion of the tree (Figure 3), particularly on newly planted or stressed trees. Bark beetles usually attack trees that are weakened by stressors such as drought, injury and disease. Though bark beetle infestation can contribute to the decline and death of trees, they are rarely the sole or primary cause of tree mortality.

Management

Primary management tactics

Keeping trees healthy is the best way to prevent injury from Ips beetles and other bark beetles. Proper pruning, fertilization and irrigation can all reduce plant stress, and ensure that trees have sufficient resources to defend against beetle attacks. Avoid harboring or introducing beetles to new areas by removing and destroying infested greenwood promptly. Chemical treatment is rarely recommended as trees attacked by bark beetles are usually already in decline.

Physical

• Chipping or debarking fresh cut wood will destroy the Ips beetle

Biological

• Woodpeckers will prey on larvae under the bark and can reduce bark beetle population sizes

Cultural

• Keep trees healthy with adequate water and fertilization
• Prune out and dispose of bark-beetle-infested limbs
• Remove freshly cut wood away from evergreen species
• Keep trees healthy with adequate water
• Avoid root damage to trees
• Plant tree species that fit your growing zone and will grow vigorously

Chemical

• Chemical treatments are rarely recommended. Treatments are only available to prevent beetle entry, and healthy trees can fend off attack without chemical intervention. Furthermore, infested trees are usually already in decline.
• Insecticides can be used as a preventative bark spray or drench before beetles enter the tree
• Recommendations for pesticides to use in the management of Ips beetle can be found on the PNW Insect Management Handbooks website
• Once beetles have entered the tree there are no chemical treatments available

Further reading

Monitoring

Monitor for bark beetles in stressed or weakened trees. Stress often occurs in old or newly planted trees, as well as in trees that are crowded. Slow growth can also be a sign of stress. In late spring, begin looking for small holes, about 0.08 inch (2 mm) in diameter, in the bark of branches that are oozing sap, contain sawdust-like frass and/or are plugged with a gummy secretion. Later in the season, look for yellowish or reddish-brown boring dust in bark crevices and around the base of trees, and for exit holes in a “shothole” pattern. Woodpeckers may also be a sign that you have bark beetles as they feed on beetles dwelling under the bark. There are pheromone-based monitoring and control techniques available but consult with your local extension expert before attempting these techniques.

Pesticide warning

Always read and follow the instructions printed on the pesticide label. The pesticide recommendations in this University of Idaho webpage do not substitute for instructions on the label. Pesticide laws and labels change frequently and may have changed since this publication was written. Some pesticides may have been withdrawn or had certain uses prohibited. Use pesticides with care. Do not use a pesticide unless the specific plant, animal or other application site is specifically listed on the label. Store pesticides in their original containers and keep them out of the reach of children, pets and livestock.

Trade names — To simplify information, trade names have been used. No endorsement of named products is intended nor is criticism implied of similar products not mentioned.

Groundwater — To protect groundwater, when there is a choice of pesticides, the applicator should use the product least likely to leach.

Andy West, Extension educator, horticulture
2023