George Fuller, then Director of Pukekura Park, New Plymouth, observed fungus gnats pollinating
N. iridescens. His contemporary diaries are transcribed here, and his photographs are below - Ed.

1979

16 Aug Pukekura Park Fernery House No 1. Dense colony of Nematoceras iridescens* in full bloom, several hundred in a m2 on an almost vertical bank. Several mosquito-like flies noted, three of them bearing on the head pollen masses of the orchid. Photographs taken & the violent efforts observed of this rather long-legged insect trying to extricate itself from a bloom

28 Aug Specimen noticed with pollen & after a great stroke of luck in that it landed on the end of a nearby pointed leaf, it was caught for preservation. (Mycetophylla diffusa Tonnoir 1927). N. papa is now in full bloom amongst the N. iridescens but no insects noted paying attention to it.

3 Sep Insect with pollen noticed on later form of N. iridescens in No 2 House. R Bickerstaff of Napier on hand to photograph it.

9 Sep Several specimens noticed in vicinity of later form of N. iridescens in House No 2 but none with pollen. Extremely active and strongly attracted to blooms. Two caught and preserved, one having entered a bloom but probably not far enough to remove pollen (Mycetophylla colorata Tonnoir 1927). The other, with striped abdomen, had not been seen to alight on any blooms (M. subspinigera Tonnoir 1927). In House No 1 most blooms of both spp. are almost over yet no flies have been observed near the slightly later N. papa. The later form of N. iridescens in House No 2 is attracting flies but the N. papa now in full bloom there has not been seen to attract any.

11 Sep Another specimen with pollen on head observed on bloom of N. iridescens in House No 2. It eluded capture by flying away. Several other specimens in flight were seen in the area of these late blooms but they moved very rapidly when disturbed. Weather was sunny & warm.

26 Sep The plant of N. iridescens on which a fly was seen bearing a pollen mass (House No 2, 3 Sep) now has a very well formed seed pod. Several other plants in the same vicinity have likewise, but none occur on the N. papa nearby. Could this fly be pollinating N. iridescens only?
 

1980

6 July Gnat noted on very early bloom of Nematoceras iridescens.

8 July Male and female, apparently copulating noted on same bloom. No pollen. Several photos taken. Female larger on filamentous petal.

11 July One gnat observed.

22 July N. papa commencing to open. Gnats very prevalent.

31 July N. papa now open in quantity but little apparent attraction for gnats. Had great success in catching specimens. Over half appear to be bearing pollen.

4 Aug Further efforts at catching all gnats observed in order to obtain an average sample of insect species, sex and number bearing pollen. Observation suggests that possibly a little over half are bearing pollen. Insect movements somewhat clumsy, some seen landing on leaves, & in one case on a bloom of N. papa but perhaps by accident, since they appear to almost "dance" on the labellum of N. iridescens. Specimens caught added to those of 31 July.

26 Aug Few specimens of N. iridescens in the mixed colony in No 1 House now in flower but N. papa at its peak. Some gnats still present but in much less numbers than when N. iridescens was at its peak. None observed bearing pollen. A paler and more broad-winged gnat has been observed in small numbers over the past week.

A fungus gnat on the labellum.

 

Two gnats bearing pollinia on
their thoraces, emerging from
the labellum.

* Fuller identified the plants as Corybas macranthus and Corybas orbiculatus in his diaries, later changing the names to Corybas "A" and Corybas rivularis as nomenclature changed. They are now known as Nematoceras iridescens and N. papa, and those names have been substituted throughout for the sake of clarity.

Fuller sent a large second batch of specimens for identification, but apparently they never arrived. That is a great shame, for only one of his first three gnat species was actually bearing pollinia, so the best we can conclude is that the female of Mycetophylla diffusa is a probable pollinator of Nematoceras iridescens.

Is this is a specific orchid/insect pollination syndrome? The answer will depend on the identification of further pollinia-bearing gnats.

And what of N. papa? Does it form fruit at all? Or does it rely entirely on vegetative spread? (which might explain its rather restricted distribution, though as Eric Scanlen reminds me, it is 130km from Mt Pirongia to Makatote).

This is a remarkably vivid account by a careful observer - Ed.