Scent chemistry and pollinator attraction in the deceptive trap flowers of Ceropegia dolichophylla

Ceropegia species (Apocynaceae, Asclepiadoideae) have pitfall flowers and are pollinated by small flies through deception. It has beensuggested that these flies are attracted by floral scent. However, the scent that is emitted from Ceropegia flowers has not been studied usingheadspace and gas chromatography mass spectrometry methods. It has also been unclear whether or not the flowers are mimics of particularmodels that attract flies. In the present study, we determined the composition as well as the spatial and temporal patterns of floral scent emitted byC. dolichophylla. Furthermore, we determined the pollinators in the native (China) and non-native (Germany) range of this species, and tested thecapability of the floral scent to attract flies in the non-native range. Our data demonstrate that the floral scent, which is emitted from morning untilevening, primarily from the tips of the corolla lobes, consists mainly of spiroacetals and aliphatic compounds. Milichiid flies were commonvisitors/pollinators in the native as well as non-native range, and were attracted by floral scent in bioassays performed in the non-native range. Thecompounds emitted by C. dolichophylla are unusual for flowers, but are well known from insect pheromones and occur in the glandular secretionsof insects. The milichiid flies that visit and pollinate the flowers are kleptoparasites that feed on the prey (haemolymph or other secretions) ofpredatory arthropods, e.g. spiders, to which they are attracted by scent. Our data thus suggest that the floral scent of C. dolichophylla mimics thefeeding sites of kleptoparasitic flies.