COTESIA OROBENAE (HYMENOPTERA, BRACONIDAE), A GREGARIOUS ENDOPARASITOID OF EVERGESTIS-RIMOSALIS (LEPIDOPTERA, PYRALIDAE), AND HYPERPARASITOIDS IN VIRGINIA BRASSICA CROPS

Cotesia orobenae Forbes (Hymenoptera: Braconidae) is a gregarious endo parasitoid of the cross-striped cabbageworm (Evergestis rimosalis Guen ee) (Lepidoptera: Pyralidae), a minor pest of Brassica crops in Virgin ia. Cocoons of C. orobenae were collected, weekly, from field plots of broccoli and cabbage crops in Whitethorne, Montgomery County (VA) dur ing 1989 and 1990. Counts were also made of the eggs and larvae of E. rimosalis to determine the pest's seasonality. In January 1991, C. oro benae cocoons were collected from the held plots to see if C. orobenae overwinters within cocoons. In May 1993, trap plants bearing E. rimos alis larvae were placed among the field plants weekly to determine if C. orobenae adults are present and ovipositing early in the season. Fi eld counts of E. rimosalis eggs and larvae in 1990 indicated the occur rence of three generations off. rimosalis from June to October, but pa rasitism of larvae on trap plants by C. orobenae in May 1993 suggested that the parasitoid is present in mid-May. C. orobenae oviposits in f irst through third instar E. rimosalis and the resulting larvae feed i nternally on the developing host, exit the fourth (last) instar host, and spin cocoons in a loose mass. Mean brood size of 118 C. orobenae f ield-collected cocoon masses was 9.2 +/- 4.4 cocoons per mass. Out of 1085 cocoons, adult C. orobenae emerged from 77%, hyperparasitoids eme rged from 7%, and nothing emerged from 16%. Females accounted for 73% of the emerging C. orobenae adults. Data from field-collected cocoons suggest that C. orobenae enter diapause in late September and overwint er in cocoons. Six pupal hyperparasitoids were recovered: Isdromas lyc aenae (Howard) (Ichneumonidae); Conura (=Spilochalcis) torvina (Cresso n) and Conura (=Spilochalcis) albifrons (Walsh) (Chalcididae); Hypopte romalus tabacum (Fitch), Catolaccus cyanoideus Burks, and Trichomalops is viridescens (Walsh) (Pteromalidae). (C) 1995 Academic Press, Inc.