How to Manage Pests
UC Pest Management Guidelines
Scientific Name: Scolytus rugulosus
(Reviewed 11/09, updated 11/09)
In this Guideline:
Description of the Pest
Shothole borers are tiny brown or black beetles. Their white legless grubs mine the sapwood of the tree and often reduce it to powder. Adult females bore tiny holes in the bark and lay eggs in the cambium layer of the tree. When eggs hatch, young larvae feed and excavate a secondary gallery at right angles to the egg gallery. The outline of the gallery system resembles a centipede. There are from one to three generations each year.
Normally, a number of shothole borer adults invade a tree at the same time. Healthy trees exude resin, which usually kills the insects. If the tree has injured or weakened areas, this resin buildup does not develop and the invasion is successful. Ultimately the larvae may girdle the tree, or tree part, and cause its death.
Shothole borers invade trees that have been previously damaged. The nature of this damage dictates the course of preventive action. Maintaining trees in a sound and vigorous condition with sufficient fertilizers, water, and sunburn prevention will keep uninfested tree limbs from becoming damaged and prevent attack by this beetle. Pruning can be helpful in eliminating areas in older trees infested with shothole borer. Severely infested trees should be removed. Burn or remove all infested wood from the orchard before the growing season starts. Do not leave pruned limbs or stumps (healthy or infested) near orchards (for example, woodpiles) as beetles can emerge from these materials before they dry out and then migrate into orchards. Spraying for this insect is not recommended.
UC IPM Pest Management Guidelines:
Insects and Mites
J. A. Grant, UC Cooperative Extension, San Joaquin County
Acknowledgment for contributions to Insects and Mites:J. Colyn, Mid-Valley Ag. Services
M. Devencenzi, Devencenzi Ag. Pest Mgmt. and Research
P. McKenzie, Mid-Valley Ag. Services