Journal Number 107
February 2008

THE COLUMN

Nematoceras at Te Kauri Lodge
By Eric Scanlen

Any orchidologist, keen on a range of Nematoceras could do well to visit the Hamilton Junior Naturalists' Te Kauri Lodge on a bush clad ridge-top, along the road to Kawhia.

Ian Reid organised a field trip for the Column and himself, through Lodge Custodians Graham
and Susan Egerton, for a few days from 16 October 07. The weather was dicey so they did some orchidising on the way in, whilst it was still dry. Kaimango Road took them south off the Kawhia Road and wound through the hills to DoC's Kihi track down a ridge to the west.

A huge colony of some unknown and unflowered Nematoceras trilobum aggregate drew a spark of interest on the roadside but, on the road batter, right at the intersection - on a damp patch where one would expect this ridge to be dry - was a huge colony of a dark-flowering form of Nematoceras macranthum.

This aggregate has at least four distinct taxa according to the Column's photos and Dr. Clements' paper on Nematoceras [1] so the Column chose a healthy looking specimen to photograph (Fig. 35) inside and out because, unlike northern specimens with flowers beneath the leaves, these had their dark flowers sometimes above, sometimes below and sometimes level with the leaf.

Fig. 35. Nematoceras macranthum agg. Near Te Kauri Lodge.		Fig. 36. The remains of a fungus gnat, dismembered by the Column's razor blade while making a sagittal section of the Nematoceras pictured in Fig. 35.

The sectioned flower showed the egg pocket in the labellum channel, peculiar to N. macranthum and N. trilobum agg. but very little of the pollinia was showing in the camera's viewfinder. The Column's trusty X20 lens revealed why; the pollinia were partially obscured by the earthly remains of a tiny fungus gnat, firmly stuck by its head to the stigma.

There are no records of which gnat pollinates these taxa so he made a diligent effort to photograph the microscopic fly with 105mm of extension tubes as you can see in Fig.36.

The unfortunate insect had been unwittingly dismembered by the Column's razor blade. Two hind legs showed above a legless thorax with one wing attached to the right and its slender abdomen above the wing and to the right of the legs.

No eggs show in the photos but it can be assumed that the gnat had been duped into the orchid by a pheromone telling her it was a specific(?) toadstool and thus to lay her eggs in it. The gnat had sadly got stuck in the stigma instead of contacting the pollinia, as nature programmed, and met an untimely end, its pollinating work incidentally interrupted.

Susan kindly posted the insect and orchid (which the Column had left in the fridge!) to John Early, Entomologist at the Auckland Institute and Museum. But after the long week-end, John found the half orchid reduced to mush and the gnat's bits recognisable only as Mycetophilidae i.e. one of at least 40 species in the fungus gnat family. Can any of our readers get any closer to which species of fungus gnat?

Orchids tend to be choosy with pollinators so some of those 40 species will no doubt be attracted to different Nematoceras taxa but checking them out promises to be a tedious task unless observers make a better fist of matters than the Column did! Any gnat found should be kept dry and intact then sent to an entomologist ASAP!

Please do not carve up every N. trilobum and N. macranthum that you see to find failed pollinators. Far better would be to rig up your camera by a suitable flower with a shutter triggering beam. Then the gnat will take its own photo(s) entering and/or exiting the flower with pollinia stuck to it, of course. Crack of dawn is probably the best time. Have fun!

At the lodge, which is huge and seats about 72 in the dining hall, there are well maintained tracks leading in different directions down both side of the ridge, all in native bush. The same Nematoceras trilobum leaves as from Kaimango Rd, were throughout; not a flower to be see this season but about four new seed capsules and chewed-off scapes did turn up out of a million odd plants. Next year!

That afternoon, N. acuminatum, in seed, were in a spot south of the lodge, along with a lonely Chiloglottis cornuta, only in leaf. Singularybas oblongus nearby was just in early bud, then the rain drove the doughty tourists back to the lodge for dinner. Baked beans again! Ian had inadvertently left the promised casserole at home.

19 October, in the windy drizzle, the intrepid pair tottered down the steps of Devlin's Track, across the road for the Lodge and skirting some huge limestone blocks further along. Thick along the base of the limestone were masses of dark N. macranthum, somewhat the same as the Kihi Track taxon and in peak flowering.

The minor differences, however left the Column itching to get his camera to work but not in the drizzle. More round leaves, along the bases of the limestone blocks, were N. iridescens and N. orbiculatum that Ian had previously photographed but they weren't showing flower at this time. Even the Microtis unifolia/parviflora had no flowers after an unseasonable dry spell a few weeks back seemed to have upset the orchids.

Fortunately, Pterostylis banksii were open along the driveway as were Earina mucronata at the Lodge. E. aestivalis promised a good show when its tight little buds open around New Year and Ian has seen Drymoanthus adversus thriving in the branches.

The weather and the forecast ruled out other planned forages so the bedraggled pair took their farewells and departed a most promising orchid site.

Reference

Clements MA, Phylogeny and Biogeography of Nematoceras Hook.f. (Orchidaceae) with special reference to their existence on New Zealand and Australian subantarctic islands. PowerPoint address at Hobart, 2006