Caterpillar Chemical Defense and Parasitoid Success: Cotesia congregata Parasitism of Ceratomia catalpae Evan C. Lampert & Lee A. Dyer & M. Deane Bowers Received: 9 March 2010 / Revised: 22 July 2010 / Accepted: 25 July 2010 / Published online: 4 August 2010 # Springer Science+Business Media, LLC 2010 Abstract Sequestration of plant compounds by herbivo- rous insects as a defense against predators is well documented; however, few studies have examined the effectiveness of sequestration as a defense against para- sitoids. One assumption of the “nasty host” hypothesis is that sequestration of plant defense compounds is deleterious to parasitoid development. We tested this hypothesis with larvae of the sequestering sphingid Ceratomia catalpae, which is heavily parasitized by the endoparasitoid Cotesia congregata, despite sequestering high concentrations of the iridoid glycoside catalpol from their catalpa host plants. We collected C. catalpae and catalpa leaves from six popula- tions in the Eastern US, and allowed any C. congregata to emerge in the lab. Leaf iridoid glycosides and caterpillar iridoid glycosides were quantified, and we examined associations between sequestered caterpillar iridoid glyco- sides and C. congregata performance. Caterpillar iridoid glycosides were not associated with C. congregata field parasitism or number of offspring produced. Although wasp survival was over 90% in all populations, there was a slight negative relationship between caterpillar iridoid glycosides and wasp survival. Iridoid glycosides were present in caterpillars at levels that are deterrent to a variety of vertebrate and invertebrate predators. Thus, our results support the alternative hypothesis that unpalatable, chem- ically defended hosts are “safe havens” for endoparasitoids. Future trials examining the importance of catalpol seques- tration to potential natural enemies of C. congregata and C. catalpae are necessary to strengthen this conclusion. Key Words Catalpa . Catalpol . Catalpa sphinx . Endoparasitoid . Iridoid glycosides . Nasty host hypothesis . Sequestration . Hymenoptera . Braconidae . Lepidoptera . Sphingidae Introduction The ability of herbivorous insects to sequester defensive compounds from their host plants has evolved in specialist and generalist species in at least four orders (Duffey, 1980; Bowers, 1990, 1993; Nishida, 2002; Opitz and Müller, 2009). Chemical defenses are among the most effective defenses of herbivores against natural enemies (Dyer and Gentry, 1999), and anti-predator defense likely is a major factor in the evolution of sequestration (Bowers, 1992). Endoparasitoids are another significant biotic source of mortality, but little is known about chemical defenses against these enemies. Endoparasitoids are insects that develop as larvae inside other insects, typically resulting in the death of the host (Godfray, 1994; Quicke, 1997). Because endoparasitoids spend their entire larval life inside the host, possible negative effects of sequestered com- pounds may be more pronounced for endoparasitoids than for predators. One hypothesis that assumes a negative effect of sequestration on endoparasitoids is the “nasty host” E. C. Lampert : M. D. Bowers (*) Museum of Natural History and Department of Ecology and Evolutionary Biology, UCB 334, University of Colorado, Boulder, CO 80309, USA e-mail: Deane.Bowers@colorado.edu L. A. Dyer Biology Department, University of Nevada, Reno, NV 89557, USA Present Address: E. C. Lampert School of Science, Technology, Engineering, and Math, Gainesville State College, Gainesville, GA 30503, USA J Chem Ecol (2010) 36:992–998 DOI 10.1007/s10886-010-9840-0