The dogwood borer, Synanthedon scitula (Harris) (Lepidoptera:Sesiidae), is a pest of a wide range of agricultural, ornamental, and landscape trees. In apple trees on size-controlling rootstocks, burr knots that are often formed below the graft union appear to be attractive oviposition sites for mated female dogwood borer and are typically where infestations originate. Currently, very little is known about the stimuli associated with oviposition site selection by mated female dogwood borer. To develop baseline data on this behavior, we examined the diurnal activity patterns and behavior of female dogwood borer on apple hosts under natural conditions. Walking surveys measuring the abundance of females observed were conducted at two-hour intervals from 0900 until 1900 hours in a .65 ha block of 4 yr old ‘Gala’ and ‘Idared’ apples on M.26 rootstock. The surveys revealed that females were observed most frequently at 15:00 hr and that more females were observed below the graft union compared with other areas of the tree. Females captured during peak periods of activity were dissected to confirm the presence or absence of a spermatophore. During peak periods of activity, the behaviors of individual females were recorded. Results showed that females spent more time searching for oviposition sites below the graft union compared with sites above the graft union or within the canopy. These results provide the basis for development of behavioral bioassays that will examine the role of olfactory stimuli in oviposition site selection by mated female dogwood borer.