Hickory Shoot Curculio Conotrachelus aratus (Germar)

Taxonomy

Domain	Eukarya
Kingdom	Animalia
Phylum	Arthropoda
Subphylum	Hexapoda
Class	Insecta
Subclass	Pterygota
Infraclass	Neoptera
Order	Coleoptera
Suborder	Polyphaga
Infraorder	Cucujiformia
Superfamily	Curculionoidea
Family	Curculionidae
Subfamily	Molytinae
Tribe	Conotrachelini
Genus	Conotrachelus

Scientific Name

Conotrachelus aratus

Common Name

hickory shoot curculio

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 hickory shoot curculio, Conotrachelus aratus (Germer), attacks pecan and hickory throughout the Eastern United States from Massachusetts south to Florida and west to Texas and Kansas (Phillips 1964, Schoff 1942, Brooks 1922). Injury results from both adult and larval feeding. Injury from larvae tunneling within the new shoots and leaf stems is most damaging, resulting in premature foliage loss and weakening or death of nut-producing shoots. Loss of terminals in young trees intended for timber production can result in forks and abnormal trunk development. Heavy damage has occurred in twigs and shoots on young budded trees in nurseries. Severe infestations are found most often on unmanaged trees or in groves adjacent to woodlands containing native pecan and hickory trees (Payne and others 1979). Fifty percent or more of the shoots can become infested. Two other curculio shoot borers, C. elegans (Say) and C. tibialis Brooks, cause injuries similar to C. aratus but are less prevalent.

Description

The adult is a weevil-type beetle with a short, stout snout that is slightly curved and about one-third the length of the body, or about as long as the head and thorax combined, and has the sternum grooved for reception of the beak (fig, 7A) (Brooks 1922, Payne and others 1979, Schoof 1942). The color is dull grayish to reddish brown with an indistinct broad band of yellowish pubescence behind the middle of the elytra and a narrow line of the same color on each side of the thorax. Adults average about 5 mm long and 2 mm wide. The egg is oval to oblong, creamy white, semitransparent, and averages 1.1 mm long and 0.7 mm in diameter. The larva is yellowish white with a brown head and black jaws and has a scattering of short but noticeable setae (fig. 7B). The larva is legless, slightly curved or cresent shaped, and averages about 6.0 mm long and 1.5 mm in diameter. The pupa is delicate and white but gradually darkens.

Evidence of Infestation

Soon after growth begins in the spring, feeding and oviposition puncture marks made by adult curculios can be found on tender shoot tips and leaf petioles (Brooks 1922, Phillips 1965, Payne and others 1979). Eggs punctures are characterized by dark triangular V-shaped marks or spots 3 mm long on the green bark. These dark puncture marks occur singly just above each leaf axil, but there may be 3 to 10 punctures per shoot. The favorite feeding place of the larva is in the bulblike swelling at the base of the leaf petiole, but it also mines in the pith of new shoots and leaf stems (fig. 8A). An active larval gallery usually has a small amount of dark frass at the entrance (fig. 8B). Dissection will reveal the cresent-shaped larvae. The burrows or galleries may range from 25 to 51 mm long (fig. 8C). The affected shoot tips and leaves usually become yellowish or brown and wither on the tree or drop away. Shoots that are heavily tunneled often break and drop without turning yellow and withering. Late summer and fall feeding by the newly emerging adults cause feeding puncture wounds along the shoot and leaf petioles, but late season damage is negligible.

Biology

The hickory shoot curculio overwinters in the adult stage in litter, trash or debris on the ground near host trees (Brooks 1922, Payne and others 1979, Schof 1942). Adults emerge from hibernation and become active in early spring as buds begin unfolding and shoot growth begins. Feeding begins in late March and April in the south and 2 to 4 weeks later in the northern range. After feeding for a short time, females deposit eggs singly in puncture niches in the tender shoot tips and leaf petioles just above the enlarged petiole base. Eggs hatch in about a week and the larvae begin feeding and tunneling within the tender new growth where they complete their larval development. When fully grown by midsummer, the mature larvae vacate their galleries, drop to the ground beneath the tree, and burrow into the soil to a depth of 12 to 51 mm where they form unlined, earthern cells for pupation. The pupal period lasts for 2 to 3 weeks. The adult curculios emerge from the ground mostly during August and September. Emerging adults are comparatively inactive and feed very little before entering hibernation in the autumn. There is one generation per year.

Control

Fifty percent or more of the larval population may be destroyed by parasities (Brooks 1922). The three species of parasities identified from the larvae are two tachnids, Myiophasia globosa (Toensend) and Cholomyiae inaequipes Bigot, and one chloropid, Chaetochlorops inquilinus (Coquillett). New plantings should be established, when possible, away from heavily infested woodlots. Sanitation and cultural practices such as clippings, collecting, and destroying infested shoots can reduce populations when only a single or few high-value trees isolated from surrounding host trees are involved. Elimination of trash and debris can also help to eliminate hibernation sites. Chemical control is usually not necessary but occasionally may be needed when many adults are present or when there is a history of damage (Payne and others 1979, Phillips 1965, Brooks 1922). Up to three spray applications, beginning in early spring when unfolding buds have 6 to 25 mm of new growth, may be necessary to control the adults before they lay their eggs.