Journal Number 108
May 2008

THE COLUMN

Thrips as Thelymitra Pollinators
By Eric Scanlen

Kevin Matthews sent the Column pix on 1 Nov 2007 from Lake Ohia, of Thelymitra aff. longifolia
"stunted" (Fig. 19) and T. pulchella (Fig. 20) with those dratted little black bugs.

Fig. 19 Black thrips on Thelymitra "sky" alba at Lake Ohia, 1 Nov 2007. The tawny wing roots are the only non-black part on this widespread species. Photo K. Matthews		Fig. 20 Black thrips carrying pollen grains. Column of Thelymitra pulchella at Lake Ohia, 1 Nov 2007. Photo K Matthews

In Fig. 20, one is carrying grains of pollen stuck to its side. We couldn't identify the minuscule bugs
then but John Early, entomologist at Auckland Museum and Institute said they looked like thrips from
the photos. Kevin caught more on film, (Fig. 23) on 7 Dec 07 also on T. pulchella at Lake Ohia.

Coincidentally, on 30 Nov 07, Ian St George sent the Column a flower bud from Shag Point, Palmerston,
of T. nervosa Col., the spotless blue T. decora.

Some will argue about these identifications of the Column's. More about that another time.

Out from Ian's column crawled a black thrips, Fig. 25, only just alive, after a day or three in the mail.
Note that "thrips" is both singular and plural like "species". The thrips' trip stripped off any pollen
it may have been carrying. It had its portraits made, but getting detail on a 0.80mm bug body with
a 35mm camera and no microscope, wasn't ever going to be easy.

Incidentally, the Column identified Ian's mystery bud as Thelymitra "bee" because of its similarity
with the Hatfields Beach colony espied on 30 Oct 1999 [J74:13,14,18]. That put another cat amongst
the pigeons: it seems that the elusive T. "bee" = spotless T. nervosa! T. "bee" has also been videoed
by Allan Ducker at Motutangi in the far north and twice at Horopito.

The Column has several photos of T. "bee" with a native bee clambering all over its column and under
the fimbria in a lost cause for pollen and nectar. Allan has video footage of the bee kicking the stuffing
out of the fimbria trying to fill its leg pockets with it which is why it is all askew in Fig. 21. The bee may
well have cross pollinated the several plants of that colony which however, never showed again at
Hatfields Beach.

Fig. 23 Thelymitra pulchella with two thrips loaded with pollen, several grains at a time. Lake Ohia, 7 Dec 07, Photo K. Matthews		Fig. 25 Thelymitra nervosa from Shag Point, 30 Nov 07. Post anther lobe with black thrips, 0.8mm long. Note the bar-like wings. Hair like wing ribs are not visible in this gross enlargement.

Stuck there on the stigma, throughout this mini-drama, was a dead thrips, trapped in the sticky stigma.
The thrips was an embarrassing distraction in the Column's 3-D shows but now becomes more
interesting.

Lying against it is a blob of presumably the orchid's own pollinium, possibly dislodged by the bee in
a case of self-pollination-by-insect but it seems the thrips got there first so any pollen it was carrying would already have fertilised some ovules.

Kevin also sent a pic of T. cyanea from Uncle Hackney Matthews' Kaitaia place Fig. 26, on 20 Jan 08.
It has been heavily enlarged, then expertly smoothed on Photoshop by Grant Scanlen. Thus the tail
bristles don't show but two blobs of pollen do, not to be confused with tawny wing roots on these thrips.

Kevin's T. sanscilia from Peria also had thrips in the column as did T. "sky" and T. pauciflora from
Cable Bay. Indubitably, these black thrips are unwittingly delivering pollen grains from flower to flower,
so must at times be cross pollinating

Thelymitra with friable pollen. Why not? Some of Kevin's photos show damage wrought by the thrips,
principally around the column. Most self respecting photographers wouldn't think of taking these
wrecks; would you?

Thus Thrips involvement in Thelymitra pollination may have continually gone unrecorded. The Column
did photograph a T. longifolia at Comet Track on 5 Dec. 1999 whilst Bruce Irwin and Bill Liddy were
changing a flat tyre. [J74 Fig. 18]. The plea on p20 for anyone to identify the tiny dead fly on the
stigma, went unanswered. Who wants anything to do with a thrips?

Fig. 21 Thelymitra nervosa (was T. "bee") at Hatfields Beach, 30 Oct 1999 where the huge(?) native bee hunting for absent nectar and loose pollen, ignores the thrips which may have given its life, pollinating the stigma		Fig. 26 Black Thrips on Thelymitra cyanea at Kaitaia on 21 Jan 08 showing pollen clusters on its wing roots and odd grains behind its head. Photo. K. Matthews, Photoshop smoothing, Grant Scanlen.

What exactly are thrips?

Reference [1] has about 3,000 species world-wide of these tiny insects and mentions Thrips tabaci
(below), a serious 2mm long pest in New Zealand. Too big to be our 0.8mm black orchid pollinator
but illustrating the essential equipment of the family. Narrow, spar-like wings with hair-like wing-ribs
but lacking any fabric covering.

Getting lift from them, is an example of nature's own nano-technology but apparently adult thrips
fly well and often. When not flying, the wings are tucked neatly down the insect's back. [2] mentions
clouds of them flying in the US of A, irritating people's skin but it also has them as important pollinators
of fruit trees. [3]

Has the New Zealand endemic, Thrips obscuratus and unidentified other species, pollinating some
13 native tree species which author Scott Norton explains, have evolved panicles of small, unscented
(to people) flowers yet attracting small pollinators. He wrote of thrips arriving at stigmas of dioecious
trees, already having male tree pollen of the same species clinging to them. That's impressive symbiosis
at work!

Norton didn't venture into orchid pollination but if trees have adapted to thrips' pollination, why wouldn't
orchids, in a country with such a paucity of pollinating insects? [4] Has a picture of exotic (for Australia)
T. obscuratus, the light brown New Zealand endemic but clearly not our black Thelymitra thrips. The text
of indecipherable entomological jargon detailed its essential characters.

Female thrips often breed without male assistance so male thrips are a rare commodity.
Don't you girls get any ideas now! Homo sapiens guys can be handy at times.

		Thrips tabaci. A 2mm long, serious New Zealand pest showing basic thrips equipment including the spar-like wings and hair-like wing ribs to provide lift. Wings tuck neatly down the bug's back when at rest.

Kevin also noted that flowers of an early (22 Sept 07), strongly perfumed Thelymitra aff. longifolia,
still emitted perfume when closed. But why? Orchids normally exude perfume selectively, for example,
only at times of day when pollinators are about, in order to conserve scarce resources.

Earina autumnalis, for instance, loses its all-pervading perfume at night so must surely have evolved
for daylight pollinators? Why then would an orchid emit perfume when closed? Tiny thrips come and
go unhindered in open or closed flowers. It could well be that they pollinate closed flowers. So theses
orchid could have evolved mostly closed, for thrips pollination, couldn't they? And we all thought it was
to protect the column details from the elements in self pollinating orchids, didn't we?

One has to wonder then, why do they open at all? Speculatively, thrips pollination, with only a few grains
of pollen at a time, would be unlikely to fill a seed capsule so the fall-back self-pollination may kick in to
fill the gap with undoubtedly second rate seeds but better than nothing.

These black thrips, possibly Dichromothrips sp according to Laurence Mound, CSIRO (pers. comm.
to Kevin) at 0.8mm long, are too small to carry pollinia (adherent pollen masses in insect pollinated
orchids) so why wouldn't orchids, pollinated by thrips, evolve mealy pollen? Thrips can easily carry
several grains of pollen at a time.

Scott Norton's Scanning Electron Microscope [3] showed two grains of tawa pollen on one crocodile-like
Thrips obscuratus' leg and ten grains of five finger pollen adhering to the armadillo-like abdomen of
another. Kevin's photos show the Thelymitra thrips, carrying pollen in small clusters on their thoraces
and sides. It seems likely that at least some of these Thelymitra species have adapted to friable pollen
not only for self pollination but also for preferential cross pollination by thrips. Cross pollinators always
outstrip asexual or self fertilised species in the struggle for supremacy so it does seem likely, doesn't it?

Charles Darwin would have been pleased at the prospect of undetected, almost invisible insects, cross
pollinating the so called self pollinating species. Ian St George, in J52:2 quotes from Darwin's 1862 first
edition on orchid fertilisation as printed below" Notice that feminine "Nature" features a capital initial;

"It is hardly an exaggeration to say that Nature tells us in the most emphatic manner that she abhors perpetual self-fertilisation." and; "I believe that orchids which do not now inter-cross, either did formerly inter-cross, or that they will do at some future period, under different conditions, unless indeed they become extinct from the evil effects of long continued close interbreeding." Perhaps no one suggested cross fertilisation by thrips to Charles?

Why does T. longifolia leave its pollen behind the stigma? T.F. Cheeseman studied the fertilisation of Thelymitra longifolia from 1876-1879, [4] on up to 103 flowers and his detailed report is recorded
in the NZNOG's Historic Series No. 4, p18-23. He noted that the flower was arranged firstly for insect
pollination then soon reverted to fall-back self pollination as the top of the pollinia drooped over the
front of the stigma.

Cheeseman did observe a thrip-like insect "sometimes abundant on the pollen on which it probably
feeds; but it is much too small to be of any service in removing the pollen from flower to flower,…".
He may have missed a vital point but remained thoughtful about the thrip-like insect's role in nature.
He pondered, if it were responsible for breaking down the pollen masses for distribution on the flower's
own stigma. He also missed a point about thrips being unhindered by closed flowers and remarked on
some species of Thelymitra "remaining closed for a large part of the day thus absolutely preventing
the access of insects."

It seems then, that the widespread, thus successful, T. longifolia, leaves the self fertilisation option to
last, as purely a fall-back system if a large insect pollinator fails to take all the pollinia (native bees
have been reported at the column, e.g. J53:10,11), then thrips may take pollen a few grains at a time,
but, as a last resort, self pollination fills those seed capsules. Even if cross pollination is only occasional,
it would be better for the survival of the species than the obligate self pollination that has often been
assumed.

Then again, why does T. cyanea have such a long, overhanging anther which lets the friable pollen flop out onto the labellum as in Fig. 24 (right)?

One would expect any self respecting self pollinator, to drop its pollen onto the broad stigma, inside the base of the column. Perhaps an extended anther is a successful adaptation for thrips or flies etc, to blunder into the scatted mealy pollen whilst feeding and carry it off to the next flower? Inevitably some to most self pollination is still going to occur as well, going by regularly full seed capsules on this and other friable pollen Thelymitra species. Australia also has T. cyanea, thrips and flies galore but no Thrips obscuratus [5].

Of the Column's five Aussie references, only one, [6] mentions pollination of T. cyanea, not selfing but "by small native bees." NZ texts too are coy about pollination of Thelymitra cyanea but Ian St George listed it as self pollinating in J52:6. From the evidence the Column believes both are right. Fig. 24 shows a typical splatter of T. cyanea's white pollen, some on its wide stigma but most has dropped straight onto the labellum, probably for bug feed and incidental transport to the next flower thus some insect pollination is catered for with selfing as merely a back-up.

There is more, don't go away. Three of our amphidiploid hybrid Thelymitra, T. decora (spotted),
T. pulchella and T. hatchii have T. longifolia as one parent, according to Molloy and Dawson [7].
The other parents are also so-called self pollinators, being T. aff. ixioides, T. cyanea and T. formosa
in the same order.

How would hybridisation happen in self pollinating orchids? Wind pollination? Not likely, not with
the adherent little clusters of pollen dropped behind the column as in T. longifolia or on the labellum
as in T. cyanea; this isn't dusty pollen like pine trees. One species of thrips, unconcerned which species
of Thelymitra they visit, could well be doing the job, over and over going by the wide variety of forms
particularly in T. pulchella, thus reflecting the many variations in both parents.

Do thrips pollinate other orchid genera? Kevin has captured another, more active, thrips species in
Spiranthes at Sweetwater and at Motutangi and observed them taking flight. Then there were those
straw coloured flies [J59:13; J75:18,19] on Earina mucronata which the Column captured unbeknown,
at Mangatangi Dam in the Hunua's on 19 Oct 1986 and on top of Mt Messenger on 19 Sept 1993 which
also have to be thrips.

Of the last, a dozen or so on one flower were biting the feet of a white footed crane fly which dared to
feed on their pollen. They were so well camouflaged that the Column didn't spot them until three years
later, when he put the x20 magnifier on the film to see what the little black dots were; they were thrips
eyes! No one was able to elucidate what they were or what they were doing in the intervening 22 years.

Please keep your eyes and x20 lenses alert in the coming season for thrips pollinating native orchids
and do tell the Editor all about any of your finds. A sequel article will cover any and all reports of
thrips in orchid flowers, especially if your camera gear and photographer are capable of depicting
these minuscule insects.

A Google search for "Thrips, Orchids, Pollinators" turned up 12,900 references, the first few indicating
that other people have investigated this subject world wide and thrips do pollinate orchids.
Why have we been so slow to cotton on in New Zealand?

The Column acknowledges all the generously given assistance from those mentioned specifically
in the text. This subject needed voicing and could not have been put together without them.

References
1. Sharell, Richard New Zealand insects and their story, Collins, 1971, 238
2. Curran, C.H. Thrips, Colliers Encyclopedia Vol. 22, 295, 1966
3. Norton, Scott A. Thrips pollination in the lowland forest of New Zealand, Dept. of Botany, Victoria Uni. of Wgn.
    http://www.newzealandecology.org/nzje/free_issues/NZJEcol7_157.pdf.
4. Cheeseman, T.F., On the Fertilization of Thelymitra, Trans. N.Z. Inst, 1880, 13: 291-6
5. Mound, Laurence, PaDIL, Pests and diseases image library, CSIRO
6. Riley, J.J. and Banks, D.P., Orchids of Australia, UNSW Press, 2002, 298
7. Dawson, M.I. and Molloy, B.P.J. Speciation in Thelymitra (Orchidacea) by natural hybridism and amphidiploidy,
    Journal of Botany Vol. 36 1998, 103-112