Influence of plant allelochemicals on the tobacco hornworm and its parasitoid, Cotesia congregata

Experiments were conducted to determine if three plant defenses affected the parasitoid Cotesia congregate in a fashion that would influence herbivore-parasitoid interactions. We evaluated the developmental rate, size, and survival of the parasitoid Cotesia congregate, when reared from Manduca sexta fed on diets containing either nic- otine, rutin, or hordenine. These results were compared to the effects of the same three chemicals on unparasitized M. sexta. The influences of the three plant defenses differed. In general, however, the effects of these allelochemicals on the parasitoid paralleled those on the unparasitized hornworm. The one major exception was that concentrations of nicotine that had little or no effect on the hornworm caused significant mortality of par- asitoids. Neither rutin nor hordenine had large or consistent negative effects, although rutin had a pronounced effect on both hornworm and parasitoid developmental times.