PHENOLOGICAL VARIATION IN CHEMICAL DEFENSE OF THE PIPEVINE SWALLOWTAIL, Battus philenor JAMES A. FORDYCE, 1, * ZACHARY H. MARION, 1 and ARTHUR M. SHAPIRO 2 1 Department of Ecology and Evolutionary Biology, University of Tennessee, Knoxville, TN 37996, USA 2 Section of Evolution and Ecology and Center for Population Biology, University of California, Davis, CA 95616, USA (Received March 11, 2005; revised August 12, 2005; accepted September 2, 2005) Abstract—Larvae of the pipevine swallowtail, Battus philenor, feed on plants in the genus Aristolochia, which contains aristolochic acids, toxic alkaloids unique to the Aristolochiaceae. Pipevine swallowtails sequester these compounds and, as a consequence, are chemically defended against many natural enemies. In California, the primary aristolochic acid present in the butterfly is aristolochic acid I. Newly eclosed adult females possess greater amounts of these sequestered toxins compared to males. However, over the course of the flight season, the aristolochic acid content of females in the population declines, whereas male aristolochic acid content remains relatively constant. Transference of sequestered aristolochic acids to eggs by females might explain the decline of these sequestered chemical defenses observed over time. We found no evidence that males transfer aristolochic acids to females via the spermatophore. The possibility that females at the end of the flight season may be automimics of males is discussed. Temporal variation in the aristolochic acid defenses exhibited by this pipevine swallowtail population is both age- and sex-dependent. Key Words—Aristolochic acid, chemical defense, sequestration, phenologi- cal variation, pipevine swallowtail, Battus philenor, automimicry. 0098-0331/05/1200-2835/0 # 2005 Springer Science + Business Media, Inc. 2835 Journal of Chemical Ecology, Vol. 31, No. 12, December 2005 ( #2005) DOI: 10.1007/s10886-005-8397-9 * To whom correspondence should be addressed. E-mail: jfordyce@utk.edu