Forest Pests: Insects, Diseases & Other Damage Agents

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

(Hylobius pales, Pachylobius picivorus, Pissodes strobi, P. nemorensis, Graphognathus leucoloma)

Weevils that damage pines can be classified as seedling debarking weevils, terminal weevils and root collar weevils. Damage from weevils can be severe when certain forestry practices favor their development.

Debarking Weevils Weevils that debark pine seedlings are the pales, H. pales, and pitch-eating, P. picivorus. These weevils damage seedlings by chewing bark from the stem above and below the ground (Figure 18). Seedlings are often girdled. Damage can be prevented or reduced when conditions favoring their development are avoided. Debarking weevils are attracted to recently logged areas with pine stumps. Adult weevils deposit eggs in roots of freshly cut pine stumps or buried slash. The larvae hatch in a few days and begin feeding beneath the bark. Upon emergence the new adults will seek out seedlings to feed on. The newly emerging weevils and older adults attack seedlings planted on or adjacent to these cut over areas. The following guidelines will help reduce weevil damage:

Figure 18 - Pitch-eating weevil photo by Terry Price

• Delay planting one year on cutover pine sites if harvest cannot be completed before July.
• If planting cannot be delayed the seedlings should be dipped in an approved insecticide or top sprayed in the nursery before lifting.
• Delay cuttings/thinnings that are adjacent to recently planted pines until the seedlings are 3-4 years old.
• Planted seedlings can be sprayed in the field with an approved insecticide if weevils begin to appear.

Terminal Feeding Weevils

Terminal weevils in the genus Pissodes are very similar in appearance and habits. The adults are 3/16”-5/16” in length depending on the species and vary in color from reddish brown to dark brown. The front wings (elytra) are marked with patches of white scales. Two common species that occur in Georgia are the white pine weevil (P. strobi) and the deodar weevil (eastern pine weevil), P. nemorensis (Figures 19 & 20).

Figure 19 - White pine weevil photo by E. Bradford Walker

Figure 20 - Deodar weevil photo by Gerald J. Lenhard

The white pine weevil attacks the terminals of white pine. Adult weevils and larvae do damage while feeding. The adults emerge in the spring and lay eggs in feeding pits they chew on the terminals. Upon hatching the larvae tunnel in the cambium often killing stems. When a terminal is killed it is replaced by an adjacent branch, which results in a crooked or forked stem (Figure 21).

Figure 21 photo from USDA Forest Service Archives

The following management recommendations have been developed to reduce losses from the white pine weevil: Plant seedlings on soils where the hardpan is three or more feet from the surface. Avoid J and L rooting of seedlings. Regenerate white pine in mixture with hardwoods. Use insecticides in Christmas tree plantings. The deodar weevil is active all winter and lays eggs in the fall and winter in small puncture holes chewed in the bark. The larvae have feeding habits

Deodar cedar is the preferred host, but loblolly, slash, shortleaf, and longleaf pines are attacked. This weevil is often found breeding in pines that have been attacked by pine bark beetles and those infected with pitch canker. The wood chip cocoons made by the larvae are readily visible underneath the bark of infested trees (Figure 22).

Figure 22 photo by Gerald J. Lenhard

No controls are necessary for the deodar weevil in forest stands.

Root Collar Weevils

The southern pine root collar weevil Hylobius aliradicis occasionally damages the roots of seedling and sapling sized loblolly and slash pines. Damage appears to be worse during droughts and on stressed trees and those with shallow roots. The larvae bore extensively in the root collar area of trees. Pupation occurs in wood chip cocoons (Figure 23). Root Debarking Weevils (Coleoptera: Graphognathus leucoloma, G. minor, and G. peregrinus) Whitefringed beetles are native to South America and were introduced into Florida in 1936. Since that time they have been found in nine states including Georgia. Three species have been described in the United States. G. leucoloma is represented by 5 races: dubious, pilosis, imitator, striatus and fecundis.

Figure 23 photo by Terry Price

Whitefringed beetles are serious pests of cotton, peanuts, okra, velvetbeans, soybeans, and sweet potatoes. The larvae and adults have been observed feeding on more than 380 species of plants. The larvae debark the taproots, whereas, the adults feed on other plant parts above ground.

During the 1980s with the advent of the Conservation Reserve Program (CRP), the whitefringed beetle became a pest of pine seedlings. The adults are dark gray with a whitish band along the outer wing margins (Figure 24). The larvae readily attack the taproots of 1-2 year old seedlings. The bark is removed all along the main taproot and the seedling dies. (Figure 25) Abandoned soybean and peanut fields may harbor residual populations of whitefringed beetles for several years.

Larvae are typical weevil-like with no apparent identifying marks. Larvae spend the winter in the soil. Adults appear in May through August. Eggs are deposited at or near ground line on vegetation. Developing larvae feed in the soil and emerge as adults the following spring. During the warmer months larvae are found in the root zone of the seedlings but in the winter they migrate downward as much as 18 inches. Fields that have lain idle for 3-4 years usually do not harbor large populations of whitefringed beetles.

Cultural practices such as scalping help reduce weevil damage by displacing and exposing the larvae in the soil. However, herbicide use increases weevil feeding on pine seedlings because native plants that serve as food for the larvae have been killed by the herbicides.

Figure 24 photo by Gerald J. Lenhard

Figure 25 photo by Terry Price

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