Eastern pine weevil adult feeding damage. Courtesy of Wood Johnson, USDA Forest Service, Bugwood.org (#1113049)
Pissodes nemorensis Germar
- Weakened, dead, or dying trees
- Occasionally on spruce and Douglas-fir
Symptoms and Signs
- Discoloration and browning (flagging) of small branches or twigs
- Small, circular holes in the main trunk or base of lower branches
- Sap excreting from circular holes
- "Chip cocoons” containing mature larvae or pupae under the bark on lower half of the tree; not found below root collar area
Causes of Similar Symptoms
- Pales weevil
- White pine weevil
Eastern pine weevil adults have long snouts typical of all weevils. The body is ½–5⁄8 inch (12–16 mm) long and 1⁄8–¼ inch (3–6 mm) wide. Females are larger than the males. The main body is covered with scalelike hairs varying from medium brown to almost black. The wing coverings have noticeable patches of white and gold scales on the rear half. Frequently, these patches are not joined.
The legless larvae are white with medium brown heads. They have sparse yellow hairs and are slightly “C” shaped. A mature larva is about ½ inch (12 mm) long. Mature larvae and pupae are found in characteristic “chip cocoons” under the bark of the tree. These structures are composed of excelsior-like strands of wood removed by the mature larvae.
Eastern pine weevil and white pine weevil are largely inseparable based only on appearance of the adults, larvae, and pupae. The two species are often found together in alcohol-and-turpentine-baited pyramidal, or Tedder’s, traps used by growers to pinpoint the emergence time of white pine weevil. Eastern pine weevil is slightly larger in all stages, but separation of the two species is difficult even for an entomologist. However, the two species reproduce in different parts of the tree, which is a reliable tool for identification. White pine weevil will only be found above the second whorl of branches. Eastern pine weevil is found on the lower trunk down to the root collar area as well as under the bark of stumps.
Biology and Life Cycle
Most eastern pine weevils overwinter as adults in the soil at the base of trees but are occasionally found near ground level in cracks and crevices in the outer bark. Very few will overwinter as larvae or pupae in the inner bark of infested trees. Adults resume activity in April and begin to feed on stumps, trunks, and large branches of healthy host trees (Figure 1). They chew a small, circular hole in the outer bark and insert their mouthparts to feed on the inner bark. Young trees and seedlings are also attractive hosts in the spring and may be killed by this feeding.
Figure 1. Adult feeding on a stump. Courtesy of Rayanne D. Lehman, PDA
After continuously feeding for about 3 weeks, the weevils move to appropriate breeding sites to mate and lay eggs. These sites include fallen trees, dying or dead trees, stumps, and sometimes trunks of stressed transplants. Females deposit eggs singly in holes chewed in the bark, preferring branch nodes to open bark areas. Eggs are commonly deposited on the lower portions of the tree, often in the shadiest spot. Oviposition is complete by midsummer, around the time the adults die. Eggs hatch in about 8 days and young larvae immediately begin feeding in the cambial layer (Figure 2). They will continue to feed along the grain of the wood, making galleries in the inner bark. Prior to pupation, larvae remove wood fibers from the xylem to create a chip cocoon in the outer bark (Figure 3). If they pupate in small transplants, the chip cocoons will be in the inner wood (Figure 4). Larvae and pupae are never found in the leader (unlike the white pine weevil) and never below the soil line (unlike the pine root collar weevil). Larvae are commonly found throughout the growing season.
Figure 2. Larva feeding under the bark of a dying tree. Courtesy of PDA
Figure 3. Larvae in a chip cocoon. Courtesy of Gerald J. Lenhard, Louisiana State University, Bugwood.org (#0014079)
Figure 4. Pupa in a chip cocoon. Courtesy of Gerald J. Lenhard, Louisiana State University, Bugwood.org (#0007009)
The majority of adults emerge 2 months after eggs are laid. Adult emergence starts in early July and can span several months due to the long oviposition period and occasional immature stages that overwinter. Most eastern pine weevils complete a generation in 1 year, but a few individuals will require 2 years. Following emergence, adults feed briefly on the bark of available stumps, healthy trees, and seedlings before overwintering (Figure 5).
Figure 5. Adult feeding on a twig. Courtesy of Rayanne D. Lehman, PDA
Calendar of Activities
Monitoring and Management Strategies
- Delay planting for 2 years in an area where pines were recently harvested.
- Remove and destroy weakened pines in perimeter of block.
- Remove and destroy stumps.
- Treat stumps from the previous season’s harvest before adult weevils become active in spring.
- Growing degree days: Overwintering adults become active from 7 to 100 GDDs.
- Destroy cull piles and weakened or dying trees before weevils become active in spring. These weevils are attracted to the resins in stumps and slash and will fly up to several miles to seek breeding material.
- Threshold level: Treat a plantation with five or more flagged tips per tree.
- At the end of the season, evaluate results and update records.
- No recommendations are available at this time.
- Remove dying or dead trees in early spring since they are good oviposition sites.
- No recommendations are available at this time.
- In early spring, treat freshly cut stumps and the surrounding soil with a registered insecticide to control ovipositing adults.
- If damage is severe, apply foliar sprays in late summer to control adults feeding on mature trees, transplants, and seedlings.
- Remove any damaged or highly susceptible trees surrounding the plantation before planting.