Neodiprion pratti pratti

Author: Eric Day, Virginia Polytechnic Institute and State University

Taxonomy

Domain	Eukarya
Kingdom	Animalia
Phylum	Arthropoda
Subphylum	Hexapoda
Class	Insecta
Subclass	Pterygota
Infraclass	Neoptera
Superorder	Holometabola
Order	Hymenoptera
Superfamily	Tenthredinoidea
Family	Diprionidae
Subfamily	Diprioninae
Genus	Neodiprion
Species	Neodiprion pratti

Scientific Name

Neodiprion pratti pratti

Common Name

Virginia pine sawfly

Distribution and Hosts

The Virginia pine sawfly has been recorded from New Jersey and Maryland to North Carolina and westward to Illinois. Its main hosts are Virginia and Shortleaf Pines, but it also feeds on Pitch and Loblolly Pines.

Description of Damage

Not considered an important defoliator pest until an outbreak in Maryland, Virginia, and North Carolina in the late 1950's swept over more than 5.6 million hectares of pine and pine-hardwood forest type. Tree mortality was only scattered, yet growth loss was severe. Heavy defoliation for two or more years can weaken trees and make them more susceptible to other mortality agents. Early instar larvae feed on the outer portion of needles. After the first two instars, larvae consume entire needles except for the basal portion within the sheath. Larvae may also feed on portions of developing buds and on tender bark of twigs.

Identification

Adults resemble flies yet have four wings instead of two. Small white oval eggs are inserted into the edge of needles at equally spaced intervals, but in only one needle fascicle. Newly hatched larvae are pale green, with black head capsules, and are 3 mm long. Full grown larvae are spotted or marked with longitudinal black stripes and are from 16 to 23 mm long. Cocoons for pupation are spun in the litter or soil surface under the trees.

Life History

Winter is spent in the egg stage and hatching occurs in early spring. Newly hatched larvae feed gregariously on the previous year's needles, beginning about 10 to 15 mm below the tip. Larval development is usually completed by the time new needles come out, giving heavily defoliated trees a tufted appearance. Mature larvae crawl to the ground in mid- May and spin their cocoons where they remain as prepupae until September when they pupate. Adults appear in October and November.

Control

White-footed mice and ants destroy large numbers of cocoons and pre-pupae in heavy infestations. An ichneumonid, Exenterus nigrifrons Rowher is an effective parasitoid of pre-pupae before they spin cocoons. An introduced parasitoid, Dahlbominus fuscipennis (Zelterstedt), has been released and established in infested stands in Virginia. A native polyhedrosis virus has destroyed up to 70 percent of sawfly larvae when applied from an airplane.

Several chemicals have proven effective in preventing damage to ornamentals. This includes the natural pathogen, Bacillus thuringiensis (B.t.), formulated as a spray and registered insecticides and their formulations, consult the most recent version of the Pest Management Guide for horticultural and forest crops, Virginia Cooperative Extension Publication 456-017.

Further Reading

Drooz, A.T. 1985. Insects of Eastern Forests. USDA For. Serv. Misc. Publ. #1426. 608 pp.

Importance

Heavy defoliation by the Virginia pine sawfly for two or more years can weaken trees and make them more susceptible to other insects and diseases, particularly when associated with drought. In commercial shortleaf pine stands, the growth loss caused by two successive years of 50 percent defoliation can amount to one-third of the expected increment over a 4-year period. This sawfly is found from New Jersey to North Carolina. The insect prefers Virginia and shortleaf pines, but will occasionally feed on pitch and loblolly pines.

Identifying the Insect

Larvae are pale green, with black head capsules, and about 1/10 inch (3 mm) long when newly hatched. Full-grown larvae are spotted or marked with longitudinal black stripes and are from 6/10 to 9/10 inch (16 to 23 mm) long. The adults have four membranous wings.

Identifying the Injury

Young larvae feed gregariously on the previous year's foliage. They consume the outer portion of the needle, causing the remaining part to take on a strawlike appearance, which is characteristic of early sawfly feeding. Mature larvae consume the entire needle and may feed on the buds and tender bark.

Biology

Adults emerge from cocoons in late October and early November. After mating, the female cuts a slit at the edge of the needle and inserts a small, white, oval egg. Several eggs are usually laid at evenly spaced intervals in each needle. Each female lays from 30 to 100 eggs. The eggs, overwinter and hatch the following April. Around mid-May, the full-grown larvae drop to the ground and spin cocoons in the litter or surface soil. They pupate in late September. There is one generation per year.

Control

Natural enemies, including a polyhedrosis virus, and adverse weather conditions seem primarily responsible for the drastic fluctuations in sawfly populations. Chemical insecticides can be used to control the sawfly.

Gallery

References

Insects and Diseases of Trees in the South. 1989. USDA Forest Service - Forest Health Protection. R8-PR16. 98 pp. Taken from http://fhpr8.srs.fs.fed.us/forstpst.html