Zimmerman Pine Moth - Dioryctria zimmermani
by Rayanne D. Lehman
Zimmerman pine moth is considered a primary pest of pines in the Midwest, but attacks on Pennsylvania trees are generally less common. When the pest does make an appearance in a Pennsylvania nursery or Christmas tree plantation, however, the damage can be significant.
Hosts and Distribution: Austrian and Scotch pines are preferred hosts, but all pines are susceptible to attack by Zimmerman pine moth. It is primarily a northern species, occur-ring in southern Canada and the northeastern and Great Lakes areas of the United States. A small, isolated population also exists in eastern Nebraska. Other species of Dioryctria are pests of pines in western and southern states.
Identification: Zimmerman pine moths, with a wingspan up to 37 mm, are the largest of the pine boring moths. Adults are rarely seen, due in part to their coloration. The forewings are mottled gray and red/brown with zigzag light and dark markings. The hindwings are yellowish white but are not visible when the moth is at rest. This color scheme and markings blend well against a pine bark background (Fig. 1). The adults are nocturnal and are not strong fliers, factors that also contribute to their elusive nature.
Actively feeding larvae are found under the bark and reach lengths of 18-25 mm at maturity. Their color varies from dirty white to pink or green, and small black spots can easily be seen at the base of some dorsal setae. Field identification generally depends upon discovery of larvae in galleries and on symptoms discussed below.
Life History: Most Zimmerman pine moth eggs are deposited on the bark of the main trunk shortly after adults emerge in late summer. Eggs are ovoid with a wrinkled surface. Initially creamy white, eggs darken to a deep reddish brown before hatching (Carls6n and Butcher 1967). After leaving the eggs, newly hatched larvae quickly move to nearby protected sites under bark scales or in crevices below a main lateral branch. They do not feed but immediately spin a silken chamber, or hibernaculum, in which they will overwinter.
In mid-April, when Scotch pine terminal growth is starting, the overwintering larvae leave the hibernaculi. They begin to feed on the bark, chewing into the inner bark. Favored points of entry appear to be succulent scar tissue around wounds and the junction of a lateral branch and main stem. The first indication of larval feeding is the appearance of frass, and possibly pitch, at these sites.
Zimmerman pine moth larvae mine inner bark anywhere on the main stem and may also feed inside the terminal shoots. Before pupating, mature larvae prepare their emergence sites by chewing away most of the bark from the inside. The pupal stage is complete in approximately 2-3 weeks, and adults emerge through the thin layer of outer bark left by the larvae. Frequently, empty pupal cases can be found protruding from adult emergence holes. Mating occurs shortly after adults emerge, usually during late July and August. Zimmerman pine moth has a single generation each year.
Damage and Detection: Damage ranges from branch dieback to death of major laterals or even the entire tree, depending on the severity and location of the infestation. Attacks on terminal shoots result in fish-hooking or browning of shoots. When larvae are feeding in the main trunk, dead tops or severe yellowing of the crown may result, while feeding in the lateral branches can kill entire branches. Frequently, limbs or trunks weakened by this pest will break in strong winds or under heavy snow load. Bark beetles may colonize trees infested by Zimmerman pine moth.
In early summer, sawdust collecting on lateral branches and in webbing on the tree is a clue to the presence of these borers. Symptoms are most pronounced in late summer, when detection of larval activity is easiest (Yonker and Schuder 1987). At this time, larvae are producing the maximum sawdust and pitch flow, and piles of coarse sawdust may be found on the soil around the base of the tree (Fig. 3). At any time of year, a creamy white to pale yellow mass of pitch mixed with frass (Fig. 4) on the large branches or main trunk is characteristic of this pest.
Control: Sanitation in and around the nursery or plantation can be helpful in reducing infestations of Zimmerman pine moth, in several ways. This pest is known to reinfest a tree year after year and removal of such "brood trees" is a recommended practice. Also, removal of older, overgrown pines that can serve as infestation sources can reduce pest occurrence. And finally, trees damaged from other causes, including Scotch pines infested with gall rust, are highly attractive to Zimmerman pine moth adults for oviposition. These trees should be eliminated, if possible.
Several larval and Trichogramma egg parasitoids have been identified in studies in southern Michigan (Carlson and Butcher 1967). Although these native parasitic wasps infested up to 57% of the Zimmerman pine moth larvae and 45% of the eggs in the study area, no parasite augmentation studies have been undertaken. Mechanical control of individual larvae can work on a limited infestation. Use a pocketknife, or other sharp object, to cut out the pitchmass and kill the larva in its gallery.
Chemical control of Zimmerman pine moth is directed against the young larvae and is most effective in spring, as the larvae emerge from the hibernaculi and begin to feed on the bark. According to spray recommendations for New York (Clark and Kowalsick 1992), a single application from early April to early May (121-246 GDD, base 500F) would be appropriate for Pennsylvania. Sprays must be directed at the main trunk and base of large branches; coverage on foliage is not necessary. Sprays against adults and newly emerged larvae in late summer and fall have not proven effective. For information about registered materials for Zimmerman pine moth, contact your regional Plant Inspector or Penn State Cooperative Extension Service.
Carlson, R.B. and J.W. Butcher. 1967. Biology and behavior of Zimmerman pine moth, Dioryctria zimmermani, in Michigan. Can. Entomol. 99:529-536.
Clark, S. and T. Kowalsick. 1992. Using growing degree-days for insect pest management. Long Island Horticulture News. Cornell Cooperative Extension. 4pp. Yonker, J.W. and D.L. Schuder. 1987. Appearance of damage symptoms and reinfestation rates for Christmas trees attacked by the Zimmerman pine moth, Dioryctria zimmermani. Great Lakes Entomol. 20: 25-29.
Vol. 24, No. 2 (Fall 1998)
Entomology Circular No. 192
PDA, Bureau of Plant Industry