Seasonal phenology and bionomics of clearwing moths in Tennessee

Larvae of clearwing moths (Lepidoptera: Sesiidae) attack and cause serious damage to more than 100 deciduous trees and shrubs in North America. Clearwing moth larvae, commonly referred to as "borers", damage plants by tunnelling beneath the bark while feeding. These borers can destroy vascular tissue and cause loss of vigor, structural weakness, branch dieback or complete girdling and death of trees (Wallace 1945, Schread 1971, Purrington and Nielsen 1977, Potter and Timmons 1983). With the isolation, characterization and synthesis of the first clearwing moth sex pheromone by Tumlinson and coworkers (1974) additional information concerning borers and their life history could be obtained (Nielsen 1979). Using these sex pheromones, numerous researchers have monitored and reported the seasonal incidence of selected adult Sesiidae (Gentry et al. 1978, Sharp et al. 1978, Neal 1981, Riedl et al. 1985, Meyer et al. 1988). A clearwing moth, Synanthedon scitula (Harris) (the dogwood borer), is one of the most serious pests of flowering dogwoods, Cornus florida L., in the eastern United States, especially in Tennessee (Pless and Stanley 1967, Williams et al. 1985). Due to the availability of a synthetic pheromone attractive to dogwood borer and the lack of information available on clearwing moths in Tennessee, a two-year study was conducted to monitor the seasonal incidence of clearwing moths in eastern and middle Tennessee and to assess infestation levels of dogwood borer on dogwood in commercial nursery, urban, and forest habitats. Eight species of clearwing moths were collected during 1987-1988 and included: Podosesia syringae (Harris), lilac borer; Paranthrene simulans "palmii" (Grote), an oak borer; Synanthedon scitula, dogwood borer; Synanthedon rhododendri (Beutenmilller), rhododendron borer: Synanthedon exitiosa (Say), peachtree borer; Synanthedon fatifera Hodges, a viburnum borer; Synanthedon acerni (Clemens), maple callous borer; and Synanthedon decipiens (Hy. Edwards), a borer of cynipid galls on oak. Lilac borers were the most abundant species collected during this two-year study and represented ca. 70% of the moths collected in the nursery and urban habitats and ca. 41% of the moths collected in the forest habitat. The dogwood borer represented ca. 10% of the moths collected in the nursery and urban habitats but was not collected in the forest habitat. Approximately 45% of the moths collected in the forest habitat were rhododendron borers. The high percentage of rhododendron borers collected in the forest habitat is a result of the large number of rhododendrons found in the forest areas sampled. The dogwood borer exhibited a bimodal period of emergence with the first peak occurring in mid-May and the second in the beginning of August. This information is important from a managerial standpoint and suggests the application of two properly timed chemical treatments for the control of dogwood borer. The highest infestation level (ca. 60%) of dogwood borer on dogwood was found in the urban habitat. The high infestation level in the urban habitat is due to adverse environmental stresses placed on the tree growing in an unnatural environment. Dogwood trees planted as ornamentals in the urban habitat are usually planted in full sun and subject to mechanical injuries (e.g. damage by lawnmowers) which increase the susceptibility of the tree to borer infestation (Potter and Timmons 1983). All nursery blocks examined were infested with dogwood borer and percent infestation averaged ca. 7%. Approximately 1% of the trees examined in the forest habitat were infested with dogwood borer.