POLLINATION OF DALECHAMPIA MAGNOLIIFOLIA (EUPHORBIACEAE) BY MALE EUGLOSSINE BEES

Flowers of Dalechampia magnoliifolia in eastern Peru were pollinated primarily by male Eulaema meriana and E. cingulata, which collected fragrance from the secretory gland borne in the staminate cymule. The fragrance contains carvone oxide, benzyl acetate, limonene, a-pinene, myrcine, f-pinene/camphene, and carvone. Trigona cf. pallens was the most abundant visitor, but was primarily a pollen thief. The rate of contact with the stigmas by Trigona, and hence the bee's efficacy as a pollinator, was highly variable and was determined by variation in the separation of anthers and stigmas. Dalechampia magnoliifolia co-occurred with a congeneric species, D. cissifolia, but did not share pollinators with it. MALE EUGLOSSINE BEES collect fragrances from flowers and other sources and apparently use them as precursors of sex pheromones (Kimsey, 1980; Williams and Whitten, 1983). Many plant species, especially orchids, utilize fragrance-collecting euglossines as pollinators (Dressler, 1968; Dodson et al., 1969; Williams and Whitten, 1983). The first report of maleeuglossine pollination in the Euphorbiaceae involved Dalechampia spathulata (Scheidw.) Baill. and male Eulaema polychroma, E. seabrai luteola, and E. cingulata in Mexico (Armbruster and Webster, 1979). In their comprehensive monograph on the genus, Pax and Hoffmann (1919) placed D. spathulata in sect. Cremophyllum along with 2 other species, D. brevipedunculata Ule and D. magnoliifolia Muell. Arg. Since pollination of D. spathulata by male euglossines was reported, there has been speculation (Whitten et al., 1986) that other members of the section might also be pollinated by male euglossines. We undertook a study ofthe pollination ecology of Dalechampia magnoliifolia in Peru to address three fundamental questions. 1) Does D. magnoliifolia, as a member of sect. Cremophyllum, produce fragrance as a floral reward, and is it visited by male euglossine bees? If so, are the fragrance and visitors different from those of D. spathulata? 2) Does D. magnoliifolia co-occur with other Dalechampia I Received for publication 26 July 1988; revision accepted 6 March 1989. Research was supported by NSF Grant No. BSR-850903 1. We thank the Departamento de Recursos Naturales of Peru for permission to work in Peru and J. Ackerman, M. E. Edwards, N. Waser, N. Williams, and an anonymous reviewer for comments on the manuscript. species, and if so, does it share visitors with them? 3) How does the effectiveness of pollinators vary with their size, and is the pollination rate for an insect species influenced by among-inflorescence variation in arrangement of flowers? MATERIALS AND METHODS-A flowering population of Dalechampia magnoliifolia was located at ca. 150 m elevation in a secondary wet forest, adjacent to a patch of relict primary forest, 10.5 km west of Yurimaguas, Loreto, Peru. We established 3 study sites 25-50 m apart, each with 2-9 flowering plants and 3-6 blossoms open at a time. Continuous observations of all flowers at each study site were made from 0830 to 1500 hr daily from 19 October to 27 October 1987. We observed activities of floral visitors daily, noting especially what floral reward the insect collected and what floral parts it contacted. Daily observations also were made on a number of developmental events, including the number of staminate flowers open, abscised, and in bud in each blossom inflorescence (pseudanthium). Stigmas were checked for pollen before and after insect visits, and glands were checked regularly for fragrance. Selected morphological measurements were made with dial calipers accurate to 0.05 mm. Fragrance samples were collected by removing 3 glands at the beginning of the period of maximum secretion (1000 hr) and placing them in a glass chamber containing powdered Tenax held in folded filter paper (Williams and Whitten, 10983). After 4 hours of exposure to the glands, the Tenax was placed in a glass ampule which was immediately sealed. The Tenax