HORTICULTURAL ENTOMOLOGY Dogwood Borer (Lepidoptera: Sesiidae) Infestation of Horned Oak Galls EILEEN A. ELIASON AND DANIEL A. POTTER Department of Entomology, University of Kentucky, Lexington, KY 40546 Ð 0091 J. Econ. Entomol. 93(3): 757Ð762 (2000) ABSTRACT Pin oak, Quercus palustris Muenchhausen, is the primary host for the gall wasp Callirhytis cornigera (Osten Sacken). Woody stem galls formed by C. cornigera may be infested by the dogwood borer, Synanthedon scitula (Harris), an important pest of ßowering dogwood, Cornus florida L. Previous research has shown that S. scitula has a bimodal seasonal ßight pattern, with peaks in late spring and midsummer. We tested the hypothesis that moths emerging from dogwoods largely account for the Þrst ßight pulse, whereas emergence from stem galls contributes disproportionately to the second pulse. Seasonal ßight activity of S. scitula was monitored with pheromone traps baited with Z,Z-3,13-octadecadien-1-ol acetate. Traps were hung near plantings of dogwoods in suburban landscapes or near heavily galled pin oaks. Borer emergence from dogwood was monitored by sampling infested trees for pupal exuviae, and from galls that were collected and held in outdoor rearing cages. The impact of S. scitula on C. cornigera larvae was assessed by weighing, measuring, and dissecting galls. Flight activity of S. scitula began on 5 May and ended on 13 October 1999, with peaks in late May and in late July to early August. The ßight pattern was similar for the two types of trapping sites, and moths emerged from both hosts during both ßight periods. Proportionately more moths emerged from dogwoods during the Þrst ßight pulse than during the second, but emergence from galls was nearly evenly divided between the two ßight peaks. We therefore reject the hypothesis that emergence of borers from galls contributes disproportionately to the second ßight period. Approximately 12Ð15% of stem galls (2Ð3 yr old) contained S. scitula larvae. Feeding and tunneling by borers contributed to gall desiccation and reduced horn development, but rarely killed C. cornigera larvae. This study has implications for management of S. scitula because borers emerging from horned oak galls may represent a threat to dogwood. KEY WORDS Synanthedon scitula, Quercus, inquiline, Sesiidae, Cynipidae, galls THE DOGWOOD BORER, Synanthedon scitula (Harris), is a native pest of woody ornamentals, especially ßower- ing dogwood, Cornus florida L., in the central and eastern United States (Potter and Timmons 1983, Eichlin and Duckworth 1988). Adults lay eggs in bark crevices, and larval feeding in the phloem and cam- bium partially or completely girdles large branches or the trunk, often leading to tree death (Weires 1986). S. scitula has the broadest host range of any North American sesiid, infesting dogwood, apple, hickory, pecan, oak, and other trees (Potter and Timmons 1981, Rogers and Grant 1990, Riedl et al. 1985). Earlier studies of dogwood borer ßight activity us- ing pheromone traps baited with Z,Z-3,13-octadeca- dien-1-ol acetate (Z,Z-ODDA) indicate that in Ken- tucky, Tennessee, and Virginia the males have a prolonged, bimodal ßight period with peaks in May to June and late July to September (Potter and Timmons 1981, Rogers and Grant 1991, Pfeiffer and Killian 1999). Based on monitoring of emergence, pupal ex- uviae left by emerging adults, and relative trap cap- tures in different habitats, Potter and Timmons (1981) suggested that the earlier ßight pulse consists largely of moths emerging from dogwood, and that the sec- ond, typically larger pulse consists mainly of adults emerging from branch cankers on apple (Malus sp.), or possibly other host trees. Seasonal ßight data from apple orchards in Virginia and Tennessee generally support this hypothesis (Rogers and Grant 1990, 1991; Pfeiffer and Killian 1999). All previous studies of S. scitula in dogwood suggest that the species is univol- tine (Pless and Stanley 1967, Potter and Timmons 1981, Eichlin and Duckworth 1988). Dogwood borers associated with apple burr knots in New York also are univoltine (Riedl et al. 1985), although some larvae may overwinter twice (Weires 1986). Besides feeding in the cambium or phloem, S. scitula also infests various insect-induced galls, including horned oak galls made by Callirhytis cornigera (Osten Sacken) (Hymenoptera: Cynipidae) (Engelhardt 1946). C. cornigera has alternating agamic and sexual generations that induce large, woody stem galls and tiny, blister-like leaf galls to form on oak trees, par- ticularly pin, Quercus palustris Muenchhausen, and willow oak, Q. phellos L. (Weld 1959, Eliason 1999). Stem galls are the most damaging stage, and form after females of the sexual generation of C. cornigera ovi- posit into the periderm, beneath the cork cambium or phellogen, in young shoots (Taft and Bissing 1988). The horn-like projections on stem galls consist of two 0022-0493/00/0757Ð0762$02.00/0  2000 Entomological Society of America Downloaded from https://academic.oup.com/jee/article/93/3/757/2217203 by guest on 28 May 2023