ABUNDANCE OF CARDIOCHILES-NIGRICEPS (HYMENOPTERA, BRACONIDAE) ON NICOTIANA SPECIES (SOLANACEAE)

The presence of adult Cardiochiles nigriceps Viereck, a nearly obligat ory parasitoid of tobacco budworm larvae, Heliothis virescens (F.) (Le pidoptera: Noctuidae), was monitored in fields with up to 117 accessio ns of Nicotiana species (Solanaceae) during 1985-1994 at Oxford, NC, T ifton, GA, and Athens, GA. Large numbers of wasps were observed flying over or resting on several Nicotlana species, especially N. noctiflor a Hooker and N. sanderae Hort. ex Watson (hybrid between N. alata Link & Otto and hi. forgetiana Hort, ex Hemsley). During the IO-vr samplin g period, an average of 60 times as many C. nigriceps adults mere coun ted in N. noctiflora plots and 19 times as many wasps were counted in N. sanderae plots than were found in commercial tobacco, N. tabacum L. ('NC 2326'), even though N. noctiflora and N. sanderae are poor host plants for tobacco budworm larvae. Male wasps predominated in plots of N. noctiflora; whereas, female wasps predominated in cultivated tobac co fields. There were no significant differences in the sex ratios of wasps collected from N. alata or N. sanderae. C. nigriceps adults were associated primarily with the flowers of, N. sanderae, N. alata, and N. forgetiana, but they were found equally on the leaves and flowers o f N. noctiflora. C. nigriceps adults appeared to be attracted to volat ile components from N. noctiflora leaves and flowers. Several kilogram s of field-grown N. noctiflora flowers and leaves were extracted with methylene chloride, and the volatile components were isolated. Gas chr omatography showed only 4 volatile peaks of interest in N. noctiflora, and they were identified as nitrogen-sulfur heterocycles.