Flatheaded appletree borer
Chrysobothris femorata (Oliver)
From: 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.
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.
Adult(s). James Solomon,
USDA Forest Service. |
Damage sap spot over attack. James Solomon,
USDA Forest Service. |
Larva(e) in gallery. James Solomon,
USDA Forest Service. |
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