By
Sandra L. Anagnostakis
A new pest
is threatening our chestnut trees. Oriental Chestnut Gall
Wasp (Dryocosmus kuriphilus) has been found on American chestnut
trees (Castanea dentata), growing along the Appalachian Trail
at the southern end of the native range of this tree. On 19
June 1993 we found galls on native-Georgia, American chestnut
trees in the Chattahoochee National Forest in northern Georgia
(Union County). This insect was brought into Georgia in 1974
from Asia, on cuttings that did not go through plant quarantine.
Chinese chestnut trees (C. mollissima Bl.) that were grown
in Georgia orchards for their nut crop, were soon infested.
The insect lays eggs in the vegetative and mixed buds and,
as the larvae develop, 1/3 to 1/2 inch, green or rose-colored
galls are formed on the leaves, petioles, and even catkins.
These galls suppress shoot elongation and reduce fruiting:
trees with severe infestations lose their vigor and often
die.
In
1963 gall wasp was reported to be threatening the chestnut
industry of Japan and Korea. Since its introduction into
Georgia, it has nearly eliminated the chestnut industry
(orchards of Chinese chestnuts) in the state. We planted
American chestnut seedlings from Southington, CT in Byron,
GA in 1989. By 1992 these trees were heavily galled by this
insect, so we knew that the danger to American trees was
serious.
Dryocosmus
kuriphilus has one generation a year in Georgia, Japan,
and Korea. The first instar larvae overwinter inside the
chestnut bud. In the spring before chestnut buds normally
begin to break, the gall wasp larvae begin to mature and
convert the bud into a gall. Galls develop in 7 to 14 days
and often contain portions of developing leaves, stems,
petioles, and flowers. The larvae feed 20 to 30 days within
the galls before pupating. Adult wasps, 1/8 inch long, begin
emerging from the galls during the last week of May and
the first week of June in Georgia. Adult emergence is complete
in approximately 3 weeks. As yet males are unknown in this
species; only female wasps have been collected in Georgia,
Japan, and Korea. After emergence, the female lays three
to five eggs in a cluster inside the buds. More than one
adult may oviposit in the same bud, and some buds may have
up to 25 eggs. The eggs hatch in 40 days, and larval growth
is very slow through the autumn and winter.
Spread
of the gall wasp occurs as a result of movement of infested
twigs or shoots, or by flight of the adults. After adult
emergence, the gall dries, becomes woodlike, and remains
attached to the tree for several years. Pruning and destroying
infested shoots may slow the spread of the insect.
Since
the Appalachian Trail extends from northern Georgia to Maine,
and since American chestnuts are found along the whole length
of the trail, there will be a source of host material for
the gall wasp to allow it to move throughout the native
range of our tree. Knowing that this pest is in their area,
the nurseries selling chestnuts in Georgia, Tennessee, and
North Carolina will be alert to the potential problem. We
are hoping to find some way of combating this problem before
we must face it in the north east.
-
Return to "The Chestnut Story" Introduction
-
Chestnuts
-
An Historical Reference for Chestnut Introductions Into
North America
-
Chestnuts And The Introduction Of Chestnut Blight
-
Oriental Chestnut Gall Wasp Found On American Chestnut
Trees
-
Valuable Chestnut Germplasm In Connecticut
-
Chestnut Breeding In The United States
-
Sources Of Chestnut Trees 1998
For
more information contact Sandra
L. Anagnostakis, The Connecticut Agricultural Experiment
Station, Box 1106, New Haven, CT 06504, phone 203-974-8498,
fax 203-974-8502.
