Pitch mass, a symptom of Zimmerman pine moth, located at the junction of a lateral branch and main stem. Courtesy of Whitney Cranshaw, Colorado State University, Bugwood.org (#1325082)
Dioryctria zimmermani (Grote)
- All pines, especially Austrian and Scotch
- Occasionally found on Douglas-fir and spruce
- Popcorn-like, white to pinkish pitch mass on trunk, often at a branch whorl or on shoots near the terminal leader; transplants and young trees may have pitch mass closer to soil line
- Reddish, sawdust-like frass mixed with pitch at entrance sites of bore holes
- Broken leader or lateral branches; dead or dying branches on upper half of tree
- Sawdust collecting on lateral branches and in webbing on the tree in early summer
- Empty pupal case protruding from wound in main trunk
Causes of Similar Symptoms
Adults, eggs, and young larvae of Zimmerman pine moths are very rarely seen. Their coloration and elusive habits help them avoid detection. Field identification is usu-ally through the presence of a pitch mass on the main trunk. This mass is popcorn-like and yellow to pinkish in color. Frass is usually mixed in with the pitch. When the glob of pitch is removed, a small, elongate/oval hole is usually found in the trunk. In an active infestation, the pitch mass will be somewhat pliable and soft. Hardened masses are generally from larval activity in the previous season.
From May to August, a single larva may be found in a short gallery in an active infestation. Zimmerman pine moth larvae are pinkish to greenish and up to an inch (25 mm) long when mature. They have a dark brown head and numerous dark spots on the body. The ¾-inch-long (18-mm) pupa may be found at the exit of the feeding tunnel from mid-July to late August.
Biology and Life Cycle
Zimmerman pine moths overwinter in the bark of the tree trunk as small caterpillars that emerged from eggs in late summer or early fall. The newly hatched caterpillars do not feed but quickly move to nearby protected sites under bark scales or in crevices below a main lateral branch. They chew small cavities in the bark and cover themselves with a silken tent, or hibernaculum, in which they will overwinter. When Scotch pine terminal growth starts the following April, the larvae leave their overwintering site and chew into the inner bark around the junction of a lateral branch and main trunk. Other favored entrance sites include wounds and galls caused by pine-pine or pine-oak gall. Small amounts of sawdust may be seen clinging to branches and in spider webs at this time.
Figure 1. Pitch mass made up of sap, frass, and tree debris that has been pushed out of the feeding tube by the larva. Courtesy of Rayanne D. Lehman, PDA
As the larvae feed in the phloem tissue, sap flows into the tunnel. Larvae push this sap—mixed with their frass and other debris—out of the tunnel, creating the characteristic pitch mass (Figure 1). Occasionally, larvae will leave one feeding site and create a second site nearby. This feeding weakens the tree branches and often causes breakage (Figures 2 and 3). Feeding continues through the summer and the larvae are mature by August (Figure 4).
Figure 2. Larva feeding within the trunk. Courtesy of Rayanne D. Lehman, PDA
Figure 3. Weakened branch junction due to Zimmerman pine moth feeding damage. Courtesy of Minnesota Department of Natural Resources Archive, Bugwood.org (#4212056)
Figure 4. Larva with pink-green body, dark brown head, and small, dark spots. Courtesy of Rayanne D. Lehman, PDA
The larvae pupate inside their feeding tunnel, close to the entrance site, or in the soft pitch mass (Figure 5). Adult moths emerge 2–3 weeks later, generally in late July through August. The short-lived adults are weak, nocturnal fliers that spend most of their time resting on the bark of the host tree (Figure 6). The coloration provides excel-lent camouflage and they are rarely seen. In late summer, each mated female deposits up to 80 eggs on the bark of the main trunk. The eggs hatch in early fall. One generation occurs each year.
Figure 5. Pupae close to the exit of the feeding tunnel. Courtesy of Rayanne D. Lehman, PDA
Figure 6. Adult moth with coloration that allows it to blend well with the tree bark. Courtesy of Whitney Cranshaw, Colorado State University, Bugwood.org (#1246008)
Calendar of Activities
Monitoring and Management Strategies
- Plant resistant varieties of Scotch pine, especially short-needled ones from Greece, Turkey, and others from south and west Eurasia.
- Observe proper planting practices, including depth of transplants. Planting too deep will lead to health issues.
- Remove and destroy heavily damaged trees. Zimmerman pine moth frequently reinfests trees; removal of these “brood” trees may lessen damage to healthy trees.
- Inspect blocks on a regular basis throughout the growing season.
- Look for pitch masses on the main trunk or near terminal leader. In young trees, masses maybe closer to soil line.
- Avoid mechanical damage to trunks that may increase susceptibility to this pest.
- Chemically or mechanically control pine galls to decrease attractive larval feeding sites.
- Growing degree days: Larvae emerge from overwintering sites at 121–246 GDDs.
- Threshold level: No threshold has been established.
- At the end of the season, evaluate results and update records.
- Many larval and Trichogramma egg parasitoids have been identified in southern Michigan. Native parasitic wasps infested up to 57 percent of larvae and 45 percent of eggs in the study area.
- Cut out areas with pitch masses on the main trunk with a pocket knife or shearing tool and use a thin wire to destroy larvae in gallery.
- Hand-prune and destroy occasional injured shoots.
- Remove and destroy (by burning or chipping) infested trees by early July before adults emerge.
- No recommendations are available at this time.
- When larvae are abundant or repeatedly attacking the main trunk, apply a registered insecticide in early April–early May as the weather warms.
— Emerging larvae are the most vulnerable to pesticides before boring under bark.
— Use enough nozzle pressure and water to drench branch and trunk bark.