Shothole Borers

Shothole Borers, This beetle is found in the eastern region of the united states NY, NJ, Connecticut.

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 the eggs hatch, young larvae feed and excavate secondary galleries 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.

Adults cause some damage by feeding at the base of small twigs, but this may not be noticed unless large numbers are present. Most of the damage is done by the larvae feeding between the bark and wood of the trunk or limbs of host trees. This damage eventually girdles the limb or trunk and kills the affected part. Adult emergence holes through the bark give the appearance of a “shot gun” blast leaving “shot holes.” The shothole borer chiefly attacks trees that have been weakened by the attacks of other borers or scale insects, winter injury, drought, disease, unsuitable soil conditions, or mechanical injury. They will, however, attack healthy trees that are near severely infested ones in which the beetles have bred in large numbers.

Life Cycle: Shothole borers overwinter as larvae in their feeding tunnels under the bark of host trees. They pupate in the spring and adults emerge in April or May. After mating, the female beetle bores through the bark and constructs an egg gallery parallel with the grain of the wood between the bark and cambium layer. The larvae feed for about one month in tunnels under the bark. After pupating and transforming to adults they chew small round holes through the bark and emerge. These small holes are the source of the common name. Soon after emergence the beetles begin to deposit eggs for another generation. There are probably three or four generations per year in Oklahoma.

The adult is a dark brown to black beetle about 1/10 inch long. The larvae are white, legless grubs with brown heads and are also about 1/10 inch long when mature.

Damage: 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, larvae may girdle the tree, or tree part, and cause its death.There has been a rise in the number of complaints about small dark brown beetles that damage and kill fruit trees. In most cases, the culprit has been identified as the shot hole borer. Poor economics, abandoned orchards, drought-stressed trees can lead to more problemswith this beetle in the future.Distributed throughout North America. Native to Europe Host Range: Cherry, peach, plum, prune, apricot, nectarine, apple, pear, quince, wild, cherry, wild plum, almond, hawthorn, ash, elm & other ornamentals.Freshly killed or diseased trees. Trees that are stressed by drought, winter injury or insect damage’s Trees with low vigor.Freshly-cut tree printings. Newly planted trees .

Control: DO NOT bother treating woodpiles with insecticides- Burn them.l WSU 2002 Crop Protection Guide will recommend endosulfan applied when adult beetles are present.l Univ. of CA- “Spraying for this insect is not recommended.”Maintain “happy” trees with proper pruning, watering & fertilization.l Scout for damage & beetles especially in early spring & late fall.l Never, ever plant new fruit trees next to an abandoned orchard or woodpile.l Consider trap logs or branches- Be sure to remove & destroy by mid-August.

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