Parasitism rates of the nonnative tachinid fly, Compsilura concinnata (Meigen), on experimental populations of native luna moth caterpillars (Actias luna (L.)) were determined in central Virginia, where both C. concinnata and the gypsy moth, its biocontrol target, have become established in the past few decades. In a forest that has not yet had gypsy moth damage, we placed cohorts of second through fifth instar Actias luna caterpillars on understory hickory trees. At the end of each instar, surviving caterpillars were collected and reared. Four parasitoid species and two hyperparasitoid species emerged from the caterpillars and pupae. C. concinnata was the most common parasitoid, attacking 0% to 62% of the caterpillars recovered in each instar. Hyperparasitism of C. concinnata by trigonalid wasps was high: 47% and 16% in the two generations. UV light census data indicate that current saturniid populations in this area of central Virginia are robust, but the long-term effects of C. concinnata introductions on populations of these and other native macrolepidoptera should be monitored.