Forest Pests: Insects, Diseases & Other Damage Agents

Conifer Defoliators Forest Health Guide for Georgia Foresters Written by Terry Price, Georgia Forestry Commission Adapted for the web by the Bugwood Network

Pine sawflies are a unique group of defoliating insects. Eleven species are described here and most are generally distributed throughout the south wherever the preferred hosts grow. The larvae consume the needles and feeding preferences are peculiar to each species. Most all sawfly species feed on old and current year foliage at some point in their development. Some species have one generation per year with defoliation occurring in the spring and others produce three or more generations with defoliation occurring on into the fall and winter. Fall and winter defoliations have greater impacts on trees and it is for this reason that sawflies having multiple generations are considered more devastating.

Sawfly adults resemble large house flies but are actually broad-waisted wasps. The females are equipped with an ovipositor that is serrated which enables them to saw little slits in the needles where eggs are laid; thus the name sawflies. It’s important for foresters to recognize sawflies and the damage they do (Figures 68-78).

Defoliation by sawflies is sporadic, occurring in localized or region wide outbreaks lasting one to several years. Growth losses the year following a severe defoliation (>75%) can average over 50 percent and mortality increases due to secondary invasions by bark beetles and pine sawyers.

The redheaded pine sawfly is the most widely distributed species in the south and is usually the species responsible for regionwide outbreaks covering several states. It is capable of producing three or more generations per year in the south (Figures A & 75).

Management practices have been developed to reduce the severity of sawflies and they should be considered before planting. Although most of the southern conifers are adaptable to a wide range of conditions it is always advisable to match the tree species to sites favoring that species. The management suggestions that may reduce the severity of sawflies are:

Figure A - Redheaded pine sawfly larvae on Longleaf photo by Terry Price

• Consider herbicides to reduce hardwood competition.
• Avoid planting on wet or droughty soils.
• Avoid sites below an index of 65.
• Monitor plantations frequently for sawfly damage. Most infestations begin on the edges of stands or are localized in a portion of the stand. Control with insecticides is most effective at this stage.

Spotted Loblolly Pine Sawfly Neodiprion taedae taedae
Figure 68 photo by Randall Blackburn
Distinctive Markings: Greenish-white, red-brown head, a dull gray-green stripe on each side of body, a row of black spots just above the midline, two black blotches on top of tenth body segment	Hosts: Loblolly and shortleaf Present: Spring to July Distribution: North Carolina, Eastern Virginia, (scattered in southeast)

Virginia Pine Sawfly Neodiprion pratti pratti
Figure 69 photo by Randall Blackburn
Distinctive Markings: Black head, body spotted or marked with longitudinal black stripes	Hosts: Virginia and shortleaf Present: Spring to July Distribution: North Carolina, Virginia, Tennessee

White Pine Sawfly Neodiprion pinetum
Figure 70 photo by Randall Blackburn
Distinctive Markings: Pale yellow with 4 rows of black spots extending from head to a black spot at tail end of body, black head	Hosts: Eastern white pine Present: Spring to July Distribution: Eastern North America

Slash Pine Sawfly Neodiprion merkeli
Figure 71 photo by Randall Blackburn
Distinctive Markings: Reddish above the eyes and sooty black below the eyes, brown stripes and two widely separated black semi-oval spots near tail end	Hosts: Slash pine Present: Spring to December Distribution: Georgia, Florida, and Mississippi

Hetrick's Sawfly Neodiprion hetricki
Figure 72 photo by Randall Blackburn
Distinctive Markings: Black head and black subdorsal and lateral stripes, (Florida specimen are pale green with faintstripes, head is pale amber and bears a yellow triangular spot with a large pentagonal marking	Distinctive Markings: Black head and black subdorsal and lateral stripes, (Florida specimen are pale green with faintstripes, head is pale amber and bears a yellow triangular spot with a large pentagonal marking Present: April to July Distribution: Virginia, Florida, South Carolina, Georgia

Warren's Sawfly Neodiprion warreni
Figure 73 photo by Randall Blackburn
Distinctive Markings: Shiny black head, broad black subdorsal, lateral and sublateral stripes	Hosts: Spruce and shortleaf pines Present: Spring to December Distribution: S.E. Arkansas to North Florida

Blackheaded Pine Sawfly Neodiprion excitans
Figure 74 photo by Randall Blackburn
Distinctive Markings: Olive green, head is glossy black, two longitudinal black stripes on the side, with a row of black spots on each side and a large black spot on the last body segment	Hosts: Loblolly and shortleaf pines (Slash, longleaf, pond, spruce, and sand pines) Present: Spring to December Distribution: Virginia to Florida and west to Arkansas and Texas (probably southwide)

Red-Headed Pine Sawfly Neodiprion lecontei
Figure 75 photo by Randall Blackburn
Distinctive Markings: Reddish head, yellowish-white body with six rows of black spots	Hosts: Shortleaf, loblolly, slash, longleaf, pitch (eastern white pine, deodar cedar) Present: Spring to December (probably year-round in South Florida) Distribution: Eastern United States

Abbott's Sawfly Neodiprion abbottii
Figure 76 photo by Randall Blackburn
Distinctive Markings: Brown to black head, thorax and abdomen pale green, four dark green to black lateral stripes	Hosts: Loblolly, shortleaf, slash, and longleaf Present: Spring to December Distribution: Wisconsin to Florida

Introduced Pine Sawfly Diprion similes
Figure 77 photo by Randall Blackburn
Distinctive Markings: Shiny black head, body has a double black strip bordered by yellow along the back; sides are dark and mottled with numerous rounded yellow and white spots	Hosts: Eastern white pine (shortleaf and Virginia pines) Present: Spring to first freeze Distribution: North Carolina, Virginia, Tennessee

Loblolly Pine Sawfly Neodiprion taedae
Figure 78 photo by Randall Blackburn
Distinctive Markings: Dull green, heavy black stripes along each side and often two lighter stripes below the heavier ones	Hosts: Loblolly and shortleaf Present: Spring to July Distribution: Arkansas, Louisiana, S.E. Texas, Mississippi, South Carolina, (Probably southwide)

The pine webworm, Tetralopha robustella, can cause extensive defoliation in young pine stands in certain years. Heavy defoliation tends to coincide with droughts. This insect primarily attacks one and two year old seedlings. When larger trees are attacked injury is usually not severe. Most Georgia pines are attacked.

Adult moths have a wingspread of 7/8 to one inch: hind wings and body are smoky gray; front wings have tufts of raised scales. Caterpillars are approximately 3/4 inch in length at maturity; tan to gray with two darker longitudinal stripes along each side. The pupae are ½ inch in length, robust and reddish.

Winter and spring are passed as pupae in the soil. In late June the adults emerge, mate and the females deposit the eggs on the needles. Weather is an important factor and greatly influences egg incubation. Cool temperatures may prolong the incubation period. The larvae hatch in August and feed on the needles. After feeding the larvae drop to the ground and pupate in an oval shaped cell. In Georgia there may be two generations per year.

Figure 79 photo by Terry Price

The larvae feed on the needles constructing masses of frass bound together with silk on the seedlings. These masses of excrement are usually 3 to 5 inches long surrounding the twigs and enclosing the basal portions of the needles (Figure 79). No control is necessary.

Pine colaspis beetle, Colaspis pini (Figure 80A), infestations appear to be more severe on pines growing along edges of grasslands and trees in isolated groups such as yard trees or trees growing in fields in clumps. In light infestations usually the edges of the year old needles on smaller trees are fed upon (Figure 80B). During heavy infestations all needles may be attacked and the tree defoliated. Cypress, spruce and most southern pines are fed upon.

Figure 80A photo by Gerald J. Lenhard

Figure 80B photo by Gerald J. Le

The adult beetles are about 3/16 inch long; rusty yellow or brown with greenish iridescence (Figure 80A). Full-grown larvae are about ¼ inch long, yellowish-white in color. The adults emerge in the summer and lay eggs in the soil. Upon hatching the larvae feed upon roots of various grasses and other vegetation. Pupation takes place in the spring and shortly after; adults begin feed-ing on the needles. There is only one generation per year.

The pine colaspis beetle is not considered an important forest insect. Heaviest feeding occurs between May and June, therefore, insecticides should be used at this time if yard trees are to be protected.

The pine chafer beetle, Anomala oblivia, periodically erupts into local severe outbreaks. Attacked trees have a scorched appearance. Adult beetles chew small notches in current year needles just above the sheath (Figure 81). Needles will often bend or break at the notched area. Although infestations can be quite spectacular little damage is done. The larvae feed on the roots of various plants including grasses.

Figure 81 - Adult pine chafer beetle photo by G. Keith Douce

Figure 82 photo by John H. Ghent

The evergreen bagworm, Thyridopteryx ephemeraeformis, is common on junipers, arborvitae, bald cypress and other conifers. The adult females are wingless and stay confined to the bag for life. The males do fly and will locate females in the fall and mate with them.s Each female may lay from 800-1000 eggs. The eggs overwinter in the female’s bag hatching in late April to early May. Upon hatching each larva constructs a small bag made from silk, portions of leaves and twigs. The bag is carried by the larva everywhere it goes. As the larva increases in size the bag is enlarged. Fully-grown bags may reach two inches or more (Figure 82).

The front end of each larva is exposed from the bag at will to enable it to feed and crawl about. The larva holds itself in the bag by a pair of prolegs attached to the tail end of its body. When disturbed or threatened the larva will quickly pull itself into the bag. The bag protects the larva from predators and insecticides. When the larva matures it attaches the bag to a twig, seals it and pupates. There is only one generation per year.

The larvae consume entire needles leaving only the sheath behind. The bags can be picked by hand and destroyed or trees can be sprayed with an insecticide just after the larvae appear.

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