Effects of comsumption of high and low nicotine tobacco byManduca sexta (Lepidoptera: Sphingidae) on survival of gregarious endoparasitoidCotesia congregata (Hymenoptera: Braconidae).

The significance of nicotine in the three trophic level interaction involving tobacco (Nicotiana tabacum), the tobacco hornworm (Manduca sexta), and the parasitoidCotesia congregata was investigated in field plots of two varieties of tobacco which had about a 10-fold difference in their nicotine content. WhileM. sexta mortality, rates of parasitism byC. congregata, and the total number ofC. 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 tobacco 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 treatment. These results support the suggestion that plant allelochemicals, which may function to provide plant resistance against pest herbivores, can be detrimental to natural enemies of the pest.