(Walker)
Solomon, J.D. 1995. Guide to Insect Borers in North American Broadleaf Trees and Shrubs. Agriculture Handbook 706. Washington, DC. United States Department of Agriculture, Forest Service. 735 p.
Contents
Hosts
Plum, peach, cherry, Chinese plum, pear, mountain-ash, persimmon, apple, white mulberry, sycamore, apricot, walnut, pecan, olive, basswood, poplar, sweetgum, yellow-poplar, gingko, elm, oak. Although this bore has a wide range of hosts, plum and other drupe and pome fruit trees appear to be favored. However, pecan and sweetgum are sometimes heavily attacked all along the Gulf Coast region.
Range
Generally distributed throughout the United States, Canada, and parts of Mexico (Heinrich 1956).
Description
Adult
Gray moth with wingspan of 17 to 28 mm (Blakeslee 1915, Forbes 1890, Heinrich 1956). Forewings grayish brown with broad, wavy bands of black and brown markings across outer third. Hindwings smoky with black marignal lines fringed with white. Head, thorax, legs, and abdomen dusky gray with bright bronze reflections.
Egg
Oval, measures, about 0.59 by 0.42 mm and opaque white and coarsely punctate. Mature egg dull red, but about 24 hours before hatching changes to dirty white with larval head plainly visible through the chlorin and slight depression appearing in center (Blakeslee 1915).
Larva
White with dark brown head when newly hatched; reddish color of alimentary tract clearly visible through integument. Mature larva with dark brown head, thoracic shield, plate, and tubercles, and reaches about 25 mm. Body color varies from dark pink or reddish gray to dusky gren (Blakeslee 1915, Forbes 1890, Sanderson 1901b).
Pupa
Ten to 12 mm long, possesses stout, hooked spines on end of abdomen and enclosed in white silken cocoon. Newly transformed pupa pale olive green but gradually changes to light brown, then to dark brown, and finally almost to black.
Biology
Moths in southern range emerge form April through September (Blakeslee 1915, Pierce and Nickels 1941). Females deposit 12 to 74 eggs singly or in small groups in cracks, crevices, or wounds in bark, and under bark scales; in the absence of such niches, eggs are loosely glued to smooth bark surfaces (Blakeslee 1915). Moths live 1 to 3 weeks but deposit most eggs during the first 2 to 4 days. Egg incubation requires 8 to 14 days. Larvae bore into bark at scars, wounds, or crevices where bark scales offer concealment and protection. Larval mines are very shallow and irregularly shaped, cave-type burrows between wood and the outer bark. Galleries usually are loosely packed with frass. Considerable frass is expelled from larval entrance holes (Sanderson 1901b). Larval feeding lasts 30 to 38 days. In the South, larvae of all sizes may be present throughout most of the growing season (Blakeslee 1915). They pupate in burrows under the bark in loosely spun silken cocoons partially surrounded by dark excrement pellets. The pupal stage lasts 24 to 33 days for the overwintering brood but may be completed in as few as 10 days for summer broods. Up to five generations occur annually in central Texas (Pierce and Nickels 1941), but only two generations in Virginia (Blakeslee 1915), Delaware (Sanderson 1901b), and Michigan (Biddinger and Howitt 1992).
Injury and Damage
New attacks can be detected by oozing sap or "weepy spots" on tree trunks (Kelsey and Stearns 1960). The most obvious signs of infestation are accumulations of dark brown or black frass on bark at attack sites (Blakeslee 1915, Pierce and Nickels 1941). The frass typically consists almost entirely of black excrement pellets that stick or adhere loosely together with sap exudate and silken threads. Attacks are limited largely to trees with mechanical wounds, frost damage, sunscalds, disease cankers, pruning wounds, and recent grafts and buds. Disease cankers and other diseased patches of the cambium or partially girdled stem are sites favored for invasion. Lifting dead bark killed by disease or other injury exposes accumulations of frass, larvae, and larvae burrows extending into the living tissue. The presence of one or more loosely woven cocoons of white silken threads is characteristic. White silken cocoons distinguish this bore from Synanthedon scitula and other sesiids, which have dark brown or black cocoons usually covered with dark frass. It attacks trees and branches of all sizes but most commonly the lower trunks, especially just above groundline. Usually not of widespread economic importance, but it can seriously damage trees in some localities. It is a major pest of cherry orchards in Michigan (Biddinger and Howitt 1992). In the late 1950's and 1960's, it seriously damaged many London plane trees in eastern cities. It prefers trees in poor health, particularly those with mechanical injuries and fungal diseases (Blakeslee 1915). Larvae on pecans may injure or destroy either grafts or patch-buds; in a Texas orchard, it destroyed two-thirds of 1,200 grafts and one-third of 3,000 patch buds (Pierce and Nickels 1941). Also, it girdles the base of sprouts that previously have been patch-budded; in a Texas pecan grove, it infested 322 of 616 sprouts on 24 top-worked trees. Deadening and felling trees and cutting back branches before top-working lower vitality and lead to maintenance of high populations of this borer (Pierce and Nickels 1941).
Control
Because eggs and first-stage larvae occur at or near the bark surface and later stages develop just under outer bark, this borer is subject to considerable parasitism and predation. Hymenopterous parasites--including Idechthis nigricoxalis (Cushman) and Mesostenus thoracicus (Cresson) in Virginia and Itoplectis marginatus (Prov.), Mesostenus gracilis Cresson, and Pimpla sp. in Georgia--destroy upwards of 14% of the larvae (Blakeslee 1915, Carlson 1979). Woodpeckers, ants, and larvae of Tenebrodies corticalis Melsh. effectively reduce populations. Use of recommended pruning, grafting, and cultivation procedures and good cultural practices in general help to prevent infestations. Tree shakers used on nut-and-fruit-producing trees should be properly adjusted or padded to avoid bruising and breaking the bark. Prompt trimming and painting of bark wounds with tar-based tree paint provide some control (Wiener and Norris 1983). Pesticides give mixed results but have provided control when properly timed and carefully applied (Kelsey and Stearns 1960, Pierce and Nickels 1941, Wiener and Norris 1983).
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