THE POLLINATION BIOLOGY OF TUCKAHOE, PELTANDRA-VIRGINICA (ARACEAE)

This study describes the specialized brood-site-based pollination syst em of Peltandra virginica Kunth (Araceae) with the chloropid fly Elach iptera formosa Loew and provides experimental evidence that gender-rel ated changes in floral odor composition synchronize pollinator behavio r with the blooming sequence. P. virginica is protogynous and does not self-pollinate because of a strong temporal separation in sexual func tion, and it is dependent upon insects for pollination because the spa the completely surrounds the spadix during the pistillate stage. Field observations conducted in central New Jersey and southeastern Pennsyl vania showed that E. formosa is closely associated with P. virginica i nflorescences. Within the floral chamber, E. formosa adults feed on po llen, mate, and find oviposition sites while the larvae complete their development. Although drosophilid and syrphid flies were collected an d reared from inflorescences of both sexual stages, only E. formosa em erged from pistillate-stage inflorescences and adult E. formosa rapidl y transferred fluorescent dye particles between inflorescences of both sexual stages in laboratory enclosures. These findings indicate that this fly species is the primary pollinator at our study locations. Fie ld censuses demonstrated that although E. formosa visited P. virginica inflorescences of both sexual stages with equal frequency, the female flies preferentially oviposited within pistillate-stage inflorescence s. Analysis of floral volatiles with gas chromatography-mass spectrome try showed that only the spathes emit the floral fragrance and that th e composition of the floral volatiles changed during the transition fr om pistillate to staminate stage. A particularly noticeable change occ urred in the emission ratio of the two primary floral odor components, 4,5,7-trimethyl-6,8-dioxabicyclo[3.2.l.]octane and an unidentified ch emical analog with molecular weight of 142. The relationship between f loral volatile composition and fly oviposition behavior was evaluated using sham inflorescences placed in the P. virginica study population. The sham inflorescences were constructed by covering spadices dissect ed from mature inflorescence buds with spathes excised from different- age inflorescences. After a 2-hr-long exposure period, sham infloresce nces fitted with pistillate-stage spathes contained more E. formosa eg gs than the sham inflorescences with staminate-stage spathes. However, the highest number of ovipositions occurred in sham inflorescences fi tted with spathes excised from mature inflorescence buds. The fragranc e emitted by these spathes was composed almost entirely of the two pri ncipal odor components. The decline in ovipositions observed in both r eal and sham inflorescences corresponded to an increase in the emissio n ratio of 4,5,7-trimethyl-6,8-dioxabicyclo[3.2.1.]octane to the molec ular weight 142 analog. This suggests that gravid flies searching for oviposition sites used the ratio of the two primary floral volatile co mponents as an inflorescence gender or age recognition cue.