REGULATORY
HORTICULTURE
[Vol. 22, No. 2]
Entomology Circular No.181
Pennsylvania Department of Agriculture
FalI 1996
Bureau of Plant Industry
Eastern
Pine Shoot Borer,
Eucosma
gloriola Heinric
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.