Abundance of Cardiochiles nigriceps (Hymenoptera: Braconidae) on Nicotiana Species (Solanaceae)

Abstract

The presence of adult Cardiochiles nigriceps Viereck, a nearly obligatory parasitoid of tobacco budworm laIvae, Heliothis virescens (F.) (Lepidoptera: Noctuidae), was monitored in fields with up to 117 accessions of Nicotiana species (Solanaceae) during 1985 – 1994 at Oxford, NC, Tifton, GA, and Athens, GA. Large numbers of wasps were obselVed flying over or resting on several Nicotiana species, especially N. noctiflora Hooker and N. sandeare Hort. ex Watson (hybrid between N. alata Link & Otto and N. forgetiana Hort. ex Hemsley). During the 10-yr sampling period, an average of 60 times as many C. nigriceps adults were counted 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 tobacco 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 of N. noctiflora. C. nigriceps adults appeared to be attracted to volatile components from N. noctiflora leaves and flowers. Several kilograms of field-grown N. noctiflora flowers and leaves were extracted with methylene chloride, and the volatile components were isolated. Gas chromatography showed only 4 volatile peaks of interest in N. noctiflora , and they were identified as nitrogen-sulfur heterocycles.