Flatheaded Appletree Borer Chrysobothris femorata (Olivier)

Taxonomy

Domain	Eukarya
Kingdom	Animalia
Phylum	Arthropoda
Subphylum	Hexapoda
Class	Insecta
Subclass	Pterygota
Infraclass	Neoptera
Order	Coleoptera
Suborder	Polyphaga
Infraorder	Elateriformia
Superfamily	Buprestoidea
Family	Buprestidae
Subfamily	Buprestinae
Tribe	Chrysobothrini
Genus	Chrysobothris

Scientific Name

Chrysobothris femorata

Common Name

flatheaded appletree borer

Solomon, J. D.; Payne, J. A. A guide to the insect borers, pruners, and girdlers of pecan and hickory. Gen. Tech. Rep. SO-64. New Orleans, LA: USDA Forest Service. Southern Forest Experiment Station; 1986. 31 p.

Importance

The flatheaded appletree borer, Chrysobothris femorata (Oliver), is a pest of pecan and hickory as well as many other deciduous trees, extending from Mexico throughout the United States into Canada (Baker 1972, Brooks 1919). It generally attacks trees that have recently been transplanted, stressed from various causes, or have bark that has been damaged by tools, disease, rodents, sun scald, or other insects. Injury results from the larvae tunneling in the bark and cambium area. Trees of all sizes may be attacked; those 5 cm or less in diameter may be girdled or killed, and larger trees may be severely weakened and scarred. Since wooded tracts often harbor high populations of beetles, damage is usually most pronounced when plantings are made in close proximity to woodland or old declining orchards.

Description

The adult is a broad, oval, flattened beetle about 7 to 16 mm in length (fig. 23A) (Brooks 1919, Moznette and others 1931). The beetle is metalic colored and indistinctly marked with spots and irregular bands of dull gray. The underside is a coppery-bronze color and the sides beneath the wings are a metallic greenish blue. The egg is pale yellow, flattened, disklike, wrinkled, and about 1.5 mm in diameter. It is firmly attached to the bark by its flat surface. The larva is yellowish white, legless, and about 25 mm long when fully grown (fig. 23B). The three thoracic segments are much broadened and compressed, giving the larva the appearance of having a large flattened head, which accounts for the name "flathead." The larvae within their galleries nearly always assume the curved shaped of a horseshoe. The pupa is somewhat more yellow than the larva and resembles the adult in structure.

Evidence of Infestation

Points of infestation can usually be detected by white, frothy sap oozing from cracks in the bark (fig. 22) (Fenton 1942, Brooks 1919, Moznette and others 1931). The bark gradually assumes a darkened, wet or greasy appearance. Little or no frass is ejected except at cracks in the bark. Injured areas usually become depressions, and later the bark may split at the injured sites. Attacks occur most often on the sunny aspect of the tree. The burrows under that bark are broad and irregular and filled tightly with fine, sawdustlike frass. In young trees with thin bark, the tunnels are usually long and winding, sometimes encircling the tree. In older trees with thick bark, the burrows are confined to a circular area under the bark. Wounds may be enlarged year after year by succeeding generations. As mentioned previously, attacks area often associated with injuries. Trunks may be attacked at any point above ground level; branches may also be attacked.

Biology

Adults appear from March to November, but they are most abundant during May and mid-August to mid-September (Fenton 1942, Moznette and others 1931). Beetles are active, run rapidly, and take flight quickly when disturbed. On hot, clear days, they may be found on the sunny side of trunks and larger branches. The female spends much time running over the surface, probing the bark with her ovipositor for places to oviposit. Females mate and begin ovipositing in 4 to 8 days; they live about 1 month after emergence. Each female lays about 100 eggs, depositing them singly in cracks or crevices of the bark, under bark scales, and at bark injuries. Eggs hatch in 8 to 16 days. The newly hatched larva chews through the bark and feeds in the phloem and surface of the sapwood. In trees sufficently weakened, the larvae produce long tortuous burrows and develop rapidly. In more vigorous trees, larval development is slow and many larvae die, probably due to heavy sap ooze. As soon as the larva is fully developed, it tunnels from the cambium area radially into the spawood where a pupal chamber is prepared by plugging the burrow tightly with frass. Here it overwinters as a larva. The larva pupates during the following spring or summer. The pupal stage lasts about 8 to 14 days. Adults emerge by cutting small oval emergence holes through the bark. Normally there is one generation per year, but some generations require 2 to 3 years.

Control

Because flatheaded borers rarely injure healthy, vigorous trees, cultural methods should be selected that keep trees vigorous, such as proper transplanting, cultivation, fertilization, spraying, pruning, thinning, and irrigation (Baker 1972, Brooks 1919, Fenton 1942, Moznette and others 1931). Since young transplanted trees are under stress and particularly susceptible, additional measures may be warrented such as wrapping the trunks with a double thickness of newspaper, burlap, and crepe paper from the ground to the lower limbs to prevent oviposition, or by shading the trunks from sunlight to deter the ovipositing females. Painting the trunks white to reduce injuries from sun scald may also help. Injuries by equipment, storm, frost, and other causes should be minimized and any fresh wounds promptly painted with pruning compound. Borers may be removed from individual trees with a knife, being careful to avoid unnecessary cutting and damage. All dead and dying trees are all pruned branches should be removed from ornamental and orchard plantings to reduce breeding sites for the beetles. Natural enemies also help to reduce flatheaded borer populations. Two ichneumonids, Labena grallator Say, Crytohelcostizus chrysobothridis Cushman, one chalcid, Phasgonophora sulcata Westwood, and one braconid, Atanycolus rugosiventris Ashm., are parasites of flathead borers; two clerids, Chariessa pilosa (Foster) and C. pilosa onusta Say, one asilid, Andrenosoma fulvicauda Say, and woodpeckers are predators.