Flatheaded Appletree Borer
From Bugwoodwiki
|
Contents |
Hosts
Pecan, hickory, apple, pear, peach, apricot, plum, cherry, quince, currant, walnut, poplar, willow, beech, chestnut, oak, elm, hackberry, sycamore, mountain-ash, serviceberry, hawthorn, redbud, maple, horsechestnut, linden, persimmon, boxelder. Maple, apple, and poplar are preferred hosts, but many other trees are also readily attacked.
Range
A pest of many deciduous trees from Mexico throughout the United States into Canada (Brooks 1919a, USDA FS 1985).
Description
Adult
Broad, oval, flattened beetle about 7 to 16 mm long (Brooks 1919a, Moznette and others 1931. Metallic hued and indistinctly marked with dull gray spots and irregular bands. Underside coppery bronze and beneath the wings metallic greenish blue.
Egg
Pale yellow, flattened, disk-like, wrinkled, and about 1.5 mm in diameter. Firmly attached to bark by their flat surfaces.
Larva
Yellowish white, legless, and about 25 mm long fully grown. Three thoracic segments much broadened and compressed, giving larva appearance of having large flattened head, which accounts for its name. Within galleries, larvae nearly always assume shape of horseshoe.
Pupa
Somewhat yellower than larva; resembles adult; 7 to 19 mm long.
Biology
Adults appear from March to November but are most abundant during May (Fenton 1942, Moznette and others 1931). Beetles, most active in full sunlight, run rapidly and take flight quickly when disturbed. On hot, clear days, beetles are found on the sunny sides of trunks and larger branches. Females spend much time running over the surface, probing the bark with their ovipositors for oviposition sites. Females mate and begin ovipositing in 4 to 8 days and live about a month. Females lay about 100 eggs each, depositing them singly in cracks or crevices of the bark, under bark scales, and at bark injuries. Eggs hatch in 8 to 16 days. Newly hatched larvae chew through the bark and feed in the phloem and surface of the sapwood. In sufficiently weak trees, larvae produce long torturous burrows and develop rapidly. In more vigorous trees, larvae develop slowly, and many die. As soon as larvae are fully developed, they tunnel from the cambium radially into the sapwood. Here, they prepare pupal chambers by plugging the burrows tightly with frass and pass the winter still as larvae within the pupal chambers. Larvae pupate for 8 to 14 days in spring or early summer. Adults emerge by cutting oval emergence holes through the bark. In most areas, one generation is produced per year, but in some areas, the species requires 2 to 3 years.
Injury and Damage
Points of infestation can usually be detected by white, frothy sap oozing from cracks in the bark (Brooks 1919a, Fenton 1942, Moznette and others 1931). Bark gradually becomes darkened, wet, and greasy in appearance. Little or no frass is ejected except at cracks in the bark. Attacks occur on both trunks and branches and are most common on the sunny aspect of trees. Burrows under the bark are broad and irregular and packed tightly with fine, sawdustlike frass. In young trees with thin bark, tunnels are usually long and winding, sometimes encircling the tree. Injured areas usually become depressed, and later the bark may split at injured sites. In older trees with thick bark, burrows are confined to a circular area within the bark. Wounds may be enlarged by succeeding generations. This borer generally attacks trees that have recently been transplanted, stressed, or whose bark has been damaged by tools, disease, rodents, sunscald, or other insects. Leaning and drought-stressed trees are especially attractive to beetles. Injury results from larvae tunneling in the bark and cambium. Trees 5 cm or less in diameter may be girdled and killed, and larger trees may be severely weakened and scarred. Because wooded tracts often harbor large populations, damage is usually most prevalent when plantings are close to woodlands or old declining orchards.
Control
Twelve species of hymenopterous parasites help to reduce infestations (Krombein and others 1979). Predators include the insects Andrenosoma fulvicauda Say, Chariessa pilosa Forester, and C. pilosa onusta Say and woodpeckers. Because flatheaded borers rarely injure healthy trees, it is most important to practice cultural methods that will keep trees vigorous (Brooks 1919a, Fenton 1942, Moznette and others 1931, USDA FS 1985). Because young transplanted trees are stressed and particularly susceptible, additional measures may be warranted such as wrapping the trunks or shading them from sunlight. Painting trunks white to reduce sunscald may also help. Borers can be physically removed from individual trees, but unnecessary cutting and damage should be avoided. Dead and dying trees and pruned branches should be removed from ornamental and orchard plantings to reduce breeding sites for the beetles. Chemical control may occasionally be required.
Gallery
 Photo by James Solomon, USDA Forest Service, Bugwood.org |  Photo by James Solomon, USDA Forest Service, Bugwood.org |
References
Solomon, J.D. 1995. Guide to insect borers of North American broadleaf trees and shrubs. Argic. Handbk. 706. Washington, DC: U.S. Department of Agriculture, Forest Service. 735 p.
