ORIENTAL CHESTNUT GALL WASP FOUND ON AMERICAN CHESTNUT TREES
Sandra L. Anagnostakis and Jerry A. Payne
The Connecticut Agricultural Experiment Station, New Haven, CT, and
U.S.D.A./A.R.S, Southeastern Fruit and Tree Nut Research Laboratory, Byron, GA
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.