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Eastern Pine Shoot Borer - Eucosma gloriola Heinric

by Rayanne D. Lehman

The eastern pine shoot borer is one of several pests that damage shoots of conifers in Pennsylvania. This damage ultimately affects the form of the tree, but does not result in tree death.

Hosts and Distribution: Eastern white pine and Scotch pine are favored hosts of this native lepidopterous pest. However, all 2- and 5-needle pines, Douglas fir, and white spruce are known hosts. Open-growing trees in pine plan­tations and natural reforestation stands are most suscepti­ble to damage within 10 years of planting. Mature stands are seldom infested.

Eastern pine shoot borer was first described from Connecticut in 1930, but subsequent collections revealed it was widely distributed in northeastern states at that time. In 1957 this pest, referred to as the white-pine shoot borer, was found damaging white pines in a Christmas tree plantation near Reading, Pennsylvania (Drooz 1960). It now occurs throughout the natural range of eastern white pine - eastern Canada, south to Virginia, and west to Minnesota.

Identification: Eucosma gloriola adults are rarely seen These small moths have wingspans of 14-l6 mm, and rest on branches of host trees during the day. Their coloration, two transverse gray bands across the coppery red forewings, is a color scheme that camouflages the moths on the similarly colored needle scales. Mature larvae are pale gray to tan, have brown heads and thoracic shields, and may be up to 13 mm long.

Workers must frequently rely on symptoms for accu­rate identification, rather than actual specimens. Eastern pine shoot borer larvae create characteristic straight tunnels, with frass tightly packed at either end (Fig 1).  In addition, the oval or oblong exit hole (Fig. 2) near the tunnel base is generally edged with discolored, reddish-brown bark.

Life History and Habits: This pest spends most of the year as a pupa in duff under the host tree. Adults emerge about the time of Scotch pine bud break (late April or early May in Pennsylvania). Researchers in Michigan use a range of 75-200 growing degree days (base 50°F) for adult emergence (Mich. St. Univ. 1996).

During a 24 week oviposition period, females deposit pale yellow, flattened eggs singly or in small groups on the new growth. Eggs hatch in l0-15 days and first-instar lar­vae enter shoots behind needle fascicles, boring directly into the pith. During the next 42-55 days, larvae feed in the pith, creating tunnels that may extend 7-29 cm, depending on the host species. They initially feed downward toward the base of the shoots but later reverse direction. This back-tracking increases the diameter of the tunnels until they are approximately twice that of the larvae. Frass pellets are packed tightly on either end of the tunnel, rather than being expelled to the outside.

Feeding is generally completed by late June, when larvae may girdle the shoot inter­nally, near the base. Larvae chew oblong or oval exit holes about 5-10cm above the base of their tunnels. After exiting through these holes, larvae drop to the ground and spin silken cocoons in the duff. Within 2 days they pupate, and remain dormant for the next 8 months.

Damaged shoots are generally empty by mid-July. Larvae are solitary feeders, and only rarely is there more than one tunnel per shoot. Those that bore into small or narrow shoots eventually chew into the vascular tissue and die from the resulting pitch flow. There is one generation each year.

Damage, Detection, and Diagnosis: Leaders and lateral shoots near tree tops are gener­ally the only portions of the host affected by the eastern pine shoot borer. Damage is gen­erally not severe unless trees are repeatedly attacked, which causes stunted, forked leaders and general loss of shape. During the year following borer attack, eastern white pines may show needleless spikes if damaged shoots fail to drop from the trees.

Pheromones for detection of eastern pine shoot borer males in spring are not commer­cially available because this insect does not cause serious economic damage. Those available for detecting the western pine shoot borer (Eucosma sonomana), an economic species in western states, are not very effective in detecting E. gloriola.

Early visual detection is difficult - infested shoots are only slightly yellowed and nee­dle elongation may be retarded. On thinner-walled shoots, larval feeding will cause wilt­ing. In fall and winter, empty shoots frequently bend over or break off at the area girdled by mature larvae, leaving short stubs.

The straight tunnel with frass packed at either end and the oblong exit hole surrounded by red-brown bark tissue are usually sufficient to distinguish this pest from other borers of pine shoots. Tunnels created by the pine shoot beetle, Tomicus piniperda (see Reg. Hort. Entomology Circular 151), are devoid of frass and have a distinctly circular entrance/exit hole that may be rimmed with sap. The two species of Rhyacionia infesting pine in Pennsylvania (European pine shoot moth, R. buoliana [Reg. Hort Entomology Circular 183], and Nantucket pine tip moth, R. frustrana [Reg. Hort. Entomology Circular 162]) generally burrow into buds and stem tissue and do not restrict their shoot feeding to the pith. These pests enter shoots and buds anywhere on the tree and do not restrict their activ­ity to upper portions.

Control: Some control of eastern pine shoot borer is generally achieved by normal shear­ing operations in Christmas tree plantations. Late shearing, however, may enhance popu­lation build-up by allowing larvae to complete their feeding and exit before the shoots are pruned. Infested trees may need special attention to correct forked tops.

Several naturally occurring wasp parasites have been identified. In a 1958 Pennsylvania study, an ichneumon wasp (Glypta sp.) parasitized 61% of the larvae in eastern white pine shoots.

Chemical controls must be in place when eggs hatch and larvae enter the new shoots.  Because this species does not cause widespread damage, sprays are not generally recommended unless more than 10 shoots per tree are damaged within 3 years of harvest.

Selected References

Benyus, J.M., ed. 1983. Christmas tree pest manual. U.S. Dep. Agric. For. Serv. No. Cent. For. Exp. Stn. St. Paul, Minn. 108 pp.

DeBoo, R.F., W.L. Sippell, and H.R. Wong. 1971. The eastern pine-shoot borer, Eucosma gloriola (Lepidoptera:Tortricidae), in North America. Can. Entomol. 103:1473-1486.

Drooz, A.T. 1960. White-pine shoot borer (Eucosma gloriola Heinrich). J. Econ. Entomol. 53:248-251.

Ives, W.G.H. and H.R. Wong. 1988. Tree and shrub insects of the prairie provinces. Can. For. Serv. Info. Rpt. NOR-X-292. 327 pp.

Michigan State University. 1996. Christmas tree insect forecast table. Mich. SL Univ. Coop. Ext. Crop Advisory Team Alert. 10(1):5.

 


REGULATORY HORTICULTURE

Vol. 22, No. 2 (FalI 1996)

Entomology Circular No.181

PDA, Bureau of Plant Industry