Journal of Chemical Ecology, Vol. 23, No. 12, 1997 VARIATION OF FLORAL SCENT EMISSION AND POSTPOLLINATION CHANGES IN INDIVIDUAL FLOWERS OF Ophrys sphegodes subsp. sphegodes FLORIAN P. SCHIESTL,1,* MANFRED AYASSE,1 HANNES F. PAULUS, 1 DIRK ERDMANN,2 and WITTKO FRANCKE2 1institute of Zoology, Department of Evolutionary Biology University of Vienna Althanstrasse 14, A-1090 Vienna, Austria 2Institute of Organic Chemistry and Biochemistry University of Hamburg, Hamburg, Germany (Received March 11, 1997; accepted August 12, 1997) Abstract—We investigated the scent composition of individual flowers of Ophrys sphegodes, its alteration following pollination, and of picked flowers by day and at night. Odor samples were collected by headspace sorption and analyzed by gas chromatography and mass spectrometry. To evaluate the function of postpollination odor changes, we carried out behavioral tests on the pollinator Andrena nigroaenea with pollinated and unpollinated flowers. We identified 27 volatiles in the flower scents. Aldehydes and alkanes were most frequently found. Aldehydes were the most abundant class of compounds (40-50%). When flowers were picked, they emitted significantly lower total amounts of volatiles than unpicked flowers, and their odor bouquets were significantly different. Comparison of scents released by day and at night showed no decrease in scent emission during nighttime, but the odor bouquets were significantly different. Pollinated flowers produced significantly different odor bouquets, and the total amount of scent emitted two to four days after pollination was significantly lower compared with unpollinated flowers. In addition, behavioral tests with A. nigroaenea males showed that flowers were significantly less attractive three days after pollination. This reduced attrac- tiveness is hypothesized to guide pollinators to the unpollinated flowers within an inflorescence, and thus increase the reproductive success of the plant. Key Words—Ophrys sphegodes subsp. sphegodes, Andrena nigroaenea, flo- ral scent, floral semiochemicals, headspace sorption, postpollination changes, nocturnal scent emission. *To whom correspondence should be addressed. 2881 0098-0331/97/1200-2881$l2.50/0 © 1997 Plenum Publishing Corporation