Many species of wild orchids have myophilous, or fly pollinated, flowers (Tan et al., 2002). The genus Bulbophyllum (Orchidaceae) has flowers that produce a foul-smelling or sweet-smelling scent to attract flies (Van der Pijl and Dodson, 1969). Bulbophyllum (Orchidaceae) is probably the largest orchid genus and contains about 1000 species (Vermeulen, 1991). The Bulbophyllum flowers selectively attract male fruit flies of several Bactrocera species (Tephritidae) (Tan, 1998). After attracting flies by the fragrance it releases, Bulbophyllum flowers ensure the removal and deposition of the pollinarium by its floral lip, which has been modified and adapted to a well-balanced structure of hinged see-saw lip that provides a floral mechanism to assist in pollination by flies (Tan et al., 2002).
Males that feed on the substances produced by these flowers, phenylpropanoids, selectively store the intact chemicals or their metabolites in the rectal glands and release them during the courtship period (Nishida et al., 1993). These compounds are known to boost the pheromone and defense systems of male flies (Tan and Nishida, 1996) while also increasing mating success, thereby greatly benefitting the males of these species (Tan and Nishida, 2000).
Acquisition of the phenylpropanoids may have evolved initially in the context of sexual selection, particularly female preference for males scented with chemicals derived from flowers (Nishida et al., 1997). In terms of coevolution between fruit flies and plants, these phenylpropanoids may mark the point at which divergence of natural fruit fly attractants occurs in the plant kingdom (Tan and Nishida, 2000). On the contrary, it may be a result of manipulation of the phenylpropanoid molecule by the plant to “convergently” attract multiple fruit fly species in a complex tropical ecosystem (Tan and Nishida, 2000).
Nishida R, Iwahashi O, and Tan KH 1993, “Accumulation of Dendrobium superbum (Orchidaceae) fragrance in the rectal glands by males of the melon fly, Dacus cucurbitaeI,” Journal of Chemical Ecology, vol. 19, pp. 713–722.
Nishida R, Shelly TE, and Kaneshiro KY 1997, “Acquisition of female-attracting fragrance by males of Oriental fruit fly from a Hawaiian lei flower, Fagraea berteriana,” Journal of Chemical Ecology, vol. 23, pp. 2275–2285.
Tan KH 1998, “Behaviour and chemical ecology of Bactrocera flies,” The Fifth International Symposium on Fruit Flies of Economic Importance, June 1–5, 1998, Penang, Malaysia.
Tan KH and Nishida R 1996, “Sex pheromone and mating competition after methyl eugenol consumption in the Bactrocera dorsalis complex,” Fruit Fly Pests—A World Assessment of their Biology and Management: Proceedings, IV International Symposium 1994, St. Lucie Press, Delray Beach, Florida.
Tan KH and Nishida R 2000, “Mutual reproductive benefits between a wild orchid, Bulbophyllum patens, and Bactrocera fruit flies via a floral synomone,” Journal of Chemical Ecology, vol. 26, no. 2, pp. 533–546.
Tan KH, Nishido R, and Toong YC 2002, “Floral Synomone of a Wild Orchid, Bulbophyllum cheiri, lures Bactrocera Fruit Flies for Pollination,” Journal of Chemical Ecology, vol. 28, no. 6, pp. 1161-1172.
Van Der Pijl L and Dodson CH 1969, Orchid Flowers—Their Pollination and Evolution, University of Miami Press, Miami, Florida, 214 pp.
Vermeulen JJ 1991, Orchids of Borneo, vol. 2—“Bulbophyllum,” Bentham-Moxon Trust, Toihaan Publishing Co. and The Sabah Society, Kota Kinabalu, Sabah, Malaysia, 342 pp.
Bulbophyllum nudda courtesy of orchids-flowers.com
Bacterocera cucurbitae courtesy of National Bureau of Agricultural Insect Resources at nbair.res.in