Sighting

Mitch Smith 13 Feb 2015

Pterostylis nutans and Mycomya sp

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Sighted 12 Jun 2014
Millers Road, Alberton West VIC 3971, Australia

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Identifications

  • Mitch Smith 13 February 2015
    Pterostylis nutans
    (species)
    Taxonomy: Plantae: Angiospermae: Monocotyledoneae: Asparagales: Orchidaceae: Pterostylis: nutans
    Common Names: Orchid family, Nodding Greenhood, Parrot's Beak Orchid
    Mitch Smith says

    Greenhood Orchids have bizarre looking flowers which have evolved to attract and utilise a specific type of Dipteroid fly known as a Fungus Gnat to initiate pollination through sexual attraction. The labellum of these orchids emit a specific kairomones(pheromone mimicking compounds) in order to attract and fool the male of this insect species into attempting to mate with this structure. As it lands on the labellum it tries to 'couple' with what it thinks is a female Fungus Gnat and through tactile stimulation is directed further into the galea(hood) of the flower. Once passed the tipping point of this hinged appendage it is triggered and forces the unsuspecting insect deep into the void. From here the small fly attempts to escape but is obscured by the labellum which blocks off the exit point, forcing the fly to take other measures. The shape and colour of the hood, which is formed by the flowers 3 fused petals, determine the direction of the new escape route. The now trapped insect is forced to traverse through a constricting passage at the rear of the flower and as it gets narrower it is positioned in the right way to have the pollen deposited on its thorax where the orchids payload is the safest. Once through this ordeal the Gnat, somewhat agitated, can continue to squeeze through the finally section, and ejects itself in a mad flurry to escape his entombment. This process can be quite quick, taking approximately a minute or so or some times it can take up to 20 mins or longer depending on certain factors, and have even been known to get trapped if not aligned correctly. It seems that sympatric orchid species have evolved over time to attract different species of Fungus Gnats in order to avoid hybridisation and some Greenhoods which don’t occupy the same habitat may rely on the same pollinator species. The pollinia seems quite large for the small mosquito sized critter but as they are strong fliers it does not seem to bother them and they fly off as usual. This process of reproduction is often overlooked in the field as the insignificant flies can be hard to spot and quite wary of activities in close proximity to them, and like other orchid pollinators can become aware of the mendacious intentions of the orchid and only falling for this ruse for a short period of time.

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