Reproductive success and pollination of the Tuncurry Midge Orchid (Genoplesium littorale) (Orchidaceae) by Chloropid Flies

Abstract

The Midge Orchids (Genoplesium R.Br.) (Orchidaceae) are thought to attract pollinators by nectar reward. All verified records of Genoplesium pollinators are small flies of the families Chloropidae and Milichiidae, suggesting pollinator specificity. We investigated pollination of the Critically Endangered Tuncurry Midge Orchid, Genoplesium littorale D.L.Jones. In common with other Genoplesium species, G. littorale is pollinated exclusively by chloropid flies. Although there is specificity at the pollinator family level, G. littorale is oligophilous, being pollinated by five putative chloropid species in two genera, Conioscinella and Cadrema. Most visitors were female with females greatly predominating among flies bearing pollinaria. Examination of flowers on ten inflorescences showed G. littorale is outcrossing with high pollen vector activity; pollinaria had been removed from 71% of post anthesis flowers. A set of criteria for distinguishing outcrossed, autogamous and apomictic flowers based on observations of pollinaria removal, pollination of stigmas and fruit set on individual flowers ruled out the occurrence of autogamy and apomixis in G. littorale. Fruit set on inflorescences averaged 44% prior to seed dispersal and varied significantly among sub-populations. Nectar is produced in the groove of the labellum callus, although flowers emitted no odour detectable by humans. Detailed examination of 29 flowers revealed no chloropid eggs, indicating the pollination syndrome is not brood site mimicry. The absence of strong dung or carrion-like odours also makes sapromyophily unlikely. The Genoplesium pollination syndrome is nectar reward, but may also represent an example of 'kleptomyiophily' , recently described in Aristolochia rotunda. Herbivory reduced reproductive capacity by half overall, varied significantly among sub-populations and may be a significant threatening process for G. littorale. Strategies to reduce herbivory in this critically endangered species should be investigated.

Pollination of Trichosalpinx (Orchidaceae: Pleurothallidinae) by biting midges (Diptera: Ceratopogonidae)

“…The evolution of kleptomyiophily has not been fully documented in Orchidaceae. However, it probably occurs in the Australian orchid Genoplesium littorale D.L.Jones as suggested by Bower, Towle & Bickel (2015).…”

Conspecific Pollen on Insects Visiting Female Flowers ofPhoradendron juniperinum(Viscaceae) in Western Arizona

“…Flowers on other plant species have been observed being pollinated or visited by the taxa of insects that carried P. juniperinum pollen to female flowers. Flies in Chloropidae and Milichiidae are known pollinators of several plant species (Larson et al 2001, Heiduk et al 2010, Bower et al 2015. Flies in both families, including Olcella and Desmometopa, have been found trapped together and covered with pollen inside pistillate flowers on tropical Aristolochia (Wolda and Sabrosky 1986).…”

Don’t forget the flies: dipteran diversity and its consequences for floral ecology and evolution

“…The greatest challenge to understanding the full spectrum of fly pollination is our collective ignorance of the life history details and ecological niches of many/most dipteran lineages (Larson et al 2001). For example, we now know that pollination by tiny kleptoparasitic frit flies (Chloropidae) can be accomplished either by feeding them nectar from flowers too small or too unapparent to be visited by more conventional pollinators (Genoplesium littorale [Orchidaceae]; Bower et al 2015), providing them with a protected, pollenbased brood site (Peltandra virginica [Araceae]; Patt et al 1995) or luring them to kettle traps whose volatiles mimic the odors of wounded or (spider-) killed insects (Aristolochia rotunda [Aristolochiaceae]; Oelschlägel et al 2015). The convergent evolution of a volatile-mediated kettle trap in chloropid-pollinated Ceropegia dolichophylla (Apocynaceae; Heiduk et al 2015) suggests that an important pollination niche has been overlooked.…”