Journal of Chemical Ecology, Vol. 12, No. 6, 1986 EFFECTS OF COMSUMPTION OF HIGH AND LOW NICOTINE TOBACCO BY Manduca sexta (LEPIDOPTERA: SPHINGIDAE) ON SURVIVAL OF GREGARIOUS ENDOPARASITOID Cotesia congregata (HYMENOPTERA: BRACONIDAE) 1 K.W. THORPE2 and P. BARBOSA Department of Entomology, University of Maryland College Park, Maryland 20742 (Received September 5, 1985; accepted December 17, 1985) Abstract--The significance of nicotine in the three trophic level interaction involving tobacco (Nicotiana tabacum), the tobacco homworm (Manduca sexta), and the parasitoid Cotesia congregata was investigated in field plots of two varieties of tobacco which had about a 10-fold difference in their nicotine content. While M. sexta mortality, rates of parasitism by C. congre- gata, and the total number of C. congregata larvae produced per host were similar on each of the two varieties, the number of parasitoids reaching adult- hood on the low nicotine treatment was nearly twice that on the high nicotine treatment. This difference was due to the significantly greater proportion of parasitoid larvae which failed to emerge from the host or that died prior to pupation after emerging from hosts which fed on the high nicotine variety. A greater proportion of larvae from hosts which fed on the low nicotine to- bacco died as pupae. No treatment differences occurred for either sex of the parasitoid in individual dry weight, longevity, or pupal development time, except that female pupal duration was prolonged in the high nicotine treat- ment. These results support the suggestion that plant allelochemicals, which may function to provide plant resistance against pest herbivores, can be det- rimental to natural enemies of the pest. Key Words--Plant allelochemical, parasitoid, three trophic level interaction, antibiosis, nicotine, tobacco, Manduca sexta, Lepidoptera, Sphingidae, Co- tesia congregata, Hymenoptera, Braconidae. Z Scientific article No. A4148 of the Maryland Agricultural Experiment Station, Department of Entomology. Research supported by NSF grant BSR-84-00614. 2 Present address: Department of Plant Science and Mechanized Agriculture, California State Uni- versity, Fresno, California 93740. 1329 0098-0331/86/0600-1329505.00/0 9 1986 Plenum Publishing Corporation