Pecan Carpenterworm Cossula magniffica (Strecker)

Taxonomy

Domain	Eukarya
Kingdom	Animalia
Phylum	Arthropoda
Subphylum	Hexapoda
Class	Insecta
Subclass	Pterygota
Infraclass	Neoptera
Superorder	Holometabola
Order	Lepidoptera
Superfamily	Cossoidea
Family	Cossidae
Subfamily	Cossulinae
Genus	Cossula

Scientific Name

Cossula magnifica

Common Name

pecan carpenterworm

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 pecan carpenterworm, Cossula magnifica (Strecker), is primarily a pest of pecan, but is also found in the hickories and reportedly some oaks throughout the Southern United States and Mexico (Baker 1972, Matz 1918, Moznette and others 1931). It attacks the branches and trunks of trees of all sizes, but shows a preference for trees 8 to 31 cm d.b.h. Small branches may break or dieback at the tunneled sites. Although very few trees break or die from carpenterworm attack, heavy repeated attacks may structurally weaken the tree, reduce its vigor, and provide entryways for decay fungi and other pathogens. The value of sawlogs and lumber from infested trees is markedly reduced because wormholes will cause the wood to be degraded. Although populations may be heavy locally, widely scattered infestations and sporadic appearance minimize the overall economic impact of the pecan carpenterworm.

Description== The adult is a grayish moth mottled with brown and black blotches (fig. 1A) (Moznette and others 1931, Baker 1972, Gill 1924). The forewings are mottled with small brown patches, and each has a large brownish area at the distal end; the hindwings are uniformly darker without distinct markings. The wingspan ranges from 37 to 44 mm. The larva is pinkish in color and naked or only sparsely covered with short fine hairs that arise from the numerous tubercles (fig. 1B). The head, cervical shield, and anal plate are shiny dark brown. The full-grown larva may reach 37 mm in length. The pupa is brown and has a sharp projection on its head that is used to help force its way through the pupal cell and along the larval burrow to the exit hole.

Evidence of Infestation

The earliest signs of attack are entrance holes, sap-stained bark, and small quantities of moist frass on the small branches during summer and early fall (Fig. 2A). Dissecting the infested branch will reveal the larval tunnel. However, these signs are often overlooked because the infested branches may be high above the ground, and the frass becomes scattered as it falls to the ground. It becomes easier to recognize the attacks when the larvae later bore into the trunk during the autumn (Moznette and others 1931, Turner and others 1918). Although attacks may occur at any point on the trunk, they are usually concentrated around the basal part of the trunk from groundline up to about 1.2 m. Attacks in the trunk are characterized by a small circular entrance hole about 6 mm in diameter with sap-stained bark below the entrance and a few excrement pellets and fine frass in bark crevices (fig. 2B). Pellet-like frass often accumulates in piles on the ground around the base of infested trees. Entrance holes are enlarged to about 9 mm just prior to pupation. Brown pupal skins may be found protruding from entrance holes during emergence in May and June. Entrances to galleries heal over leaving uniformily round or oval bark scars for several years as evidence of previous attacks.

Biology

Eggs are deposited on the bark of small branches in the tops of trees after emergence and mating of the adult moths from late April through June (Baker 1972, Moznette and others 1931, Gill 1924). The newly hatches larvae first attack small twigs and branches and tunnel out the pithy center (fig. 2B). When the larva becomes too large for the small twig, it crawls out and enters a large branch. Entrances in twigs and small branches are usually made adjacent to buds, leaf petioles, or small secondary branches. The larva may tunnel up to 10 cm in both directions from the entrance hole, leaving only shells of small branches 10 to 13 mm in diameter. By early fall the larvae vacate their branch galleries, crawl downward on the bark, and bore into the trunk and large branhces. Larvae attacking the trunk usually initiate galleries in bark crevices and tunnel horizontally or obliquely upward for 13 to 32 mm, the vertically for another 6 to 13 cm (fig. 2D). Many larvae also tunnel downward from the point of entrance another 5 to 10 cm. The cross-section of the vertical portion of the gallery is usually round, and about 6 mm in diameter. The wormholes and associated stain and decay show up as defects in the lumber. The insect overwinters as a larva within the gallery. The following April or May the mature larva enlarges the entrance hole and then encloses itself and pupates in the upper end of the gallery behind a very peculiar but characteristic barrier or network of threadlike material. The sharp projection on the head end of the pupa enables the pupa to move through the barrier and down the tunnel to the entrance hole for emergence. Entrances to vacated galleries heal over, leaving uniformly round or oval bark scars in the bark. Although little is known about the life history, there appears to be one generation per year.

Control

Although reported to occur throughout the South from North Carolina to Florida and west to Texas, infestations are generally widely scattered (Boethel and others 1980). Trees planted as ornamentals or in orchards, groves, or other open-grown situations are generally more heavily infested than those growing in well-stocked forest stands. Care should be exercised so that new plantings are not established adjacent to old orchards or stands heavily infested with carpenterworms. Keeping the trees in vigorous condition and free of disease cankers and mechanical injuries will help to prevent infestation. Two tachnid parasities, Phorocera comsticki Williston (Leiby 1925) and P. signata Aldrich and Webber have been reared, but little is know of their effects on carpenterworm populations. Small numbers of borers can be controlled by injecting a fumigant into the gallery and then using clay or putty to plug the entrance hole. Insectides used periodically in groves to control nut and foliar insects provide some, but not complete, control of carpenterworms. Chemical control specifically for pecan carpenterworm is seldom justified (Boethel and others 1980).