Journal Number 105
November 2007

AUSTRALIAN NOTES
By David McConachie

Threatened Orchids of Southwest Victoria
by Andrew Pritchard, DSE Threatened Species Project Officer
From ANOS (Vic) Bulletin 40 (1), July 2007

Andrew and a small but enthusiastic team of scientists, together with Colin Bower, an entomologist from New South Wales, conducted the following research during 2006.

Many Australian terrestrial orchids mimic female thynnine wasps and are pollinated by males trying to mate with the flower. Sexually deceptive orchid flowers are characteristically dull coloured, often inconspicuous, pollinated by males of a single specific wasp species, emit a mimic of the female sex pheromone to attract males from a distance, have labellum structures that mimic the shape and colour of the female wasp, and lack nectar and sweet odours.

Female thynnine wasps are wingless and spend most of their lives burrowing in soil and seeking beetle larvae to parasitise. They emerge every few days and advertise for males by emitting pheromones. The male wasps respond rapidly, pick up the smaller females and fly them, in copula, to nectar sources where the females feed.

Because many terrestrial orchid species are pollinator specific, if the pollinator becomes locally extinct due to habitat modification and loss of critical resources, that population will become vulnerable or locally extinct. If the pollinator becomes extinct over the whole range of the orchid, that orchid species will become totally extinct unless it has the ability to reproduce vegetatively and/or self pollinate.

The best reproduction in sexually deceptive orchids results where high orchid and pollinator populations occur together, so sexually deceptive orchids with common pollinators are usually common while orchids with rare pollinators are likely to be rare.

Knowledge of the identity of pollinators, and their distribution and abundance, may be important for developing successful recovery strategies for threatened orchid species. Recovery plans should include objectives to determine how much natural pollination is occurring; identify the pollinators; determine the distribution, abundance and habitats of pollinators; use those data to determine if habitat enhancement for pollinator populations is feasible at orchid sites or, alternatively, locate suitable sites with good pollinator populations for establishment of new self -sustaining orchid populations. In the long term, it is not a good strategy to hand pollinate to maintain orchid populations.

The project aims to collect and identify the pollinators of as many threatened and other Caladenia spp. as possible in southwest Victoria; to determine the distribution and abundance of the pollinators; and to locate potential establishment sites with large pollinator populations for rare Caladenia spp.

Sexually deceptive orchids are highly attractive to their pollinators, yet it is rare to see insects on flowers in the field. The reason is that male wasps learn to avoid the locations of non-rewarding stimuli. The secret to collecting pollinators is to provide the wasps with stimuli (flowers) at new locations, which they interpret as a potential new female. Males respond within seconds to new calling females, and most nearby males will arrive at a new flower location within a few minutes.

However, once males have learnt the stimulus at a particular location is false, they generally do not respond again. This behaviour can be exploited in the technique known as ˜baiting '.

Thirteen species of orchids were tested. No thynnine wasps were attracted to C. versicolor after 163 three minute exposures at four sites. The pink-mauve labellum markings of C. versicolor are not consistent with mimicry of female thynnine wasps, but are more like flowers pollinated by native bees. C. versicolor is also sweet-scented; another characteristic of bee-pollinated flowers. C. versicolor is most likely pollinated by native bees that also visit other purple-flowered herbs such as chocolate lilies. Bee pollination is not well documented among spider orchids, and
C. versicolor may be unique in this regard.

Lophocheilus villosus, the pollinator of C. hastata, is rare. This pollinator was not located at Point Danger, which was consistent with the lack of C. hastata pollination at this site. However, the pollinator was found at Mt. Richmond NP on the last day of the survey, and there was no time available to test whether the Casterton population attracts the same wasp. Further work is needed at both sites. Future work needs to be done on other species in New South Wales, Victoria and South Australia; there is a need to verify bee-pollination in C. versicolor; and there is a need to search for more populations of C. hastata at Point Danger and to determine the pollinator of the Casterton population. The team want to conduct specific choice tests to determine if there are three cryptic pollinator species in Phymatothynnus pygidialis; determine how many members of the C. reticulata complex share the P. var. nitidus pollinator; and determine the pollinator of
C. grampiana.

Kate Vlcek of DSE South West (Warrnambool) is working on the translocation of C. hastata. 63
C. hastata (Melbourne 's Spider Orchid) seedlings were transplanted in August 2006. Plants were four year old seedlings, the results of direct seeding trials at Point Danger. Seven previous translocations / reintroductions have taken place since 1982 with an 87% success rate. The purpose of these translocations is to perfect techniques for the future; to increase the number of sites and "spread the risk"; also to improve vigour of remaining plants at the host site where they are growing in cramped conditions.

On "The Big Day" ', the team was briefed and they scrubbed down before splitting into groups. Plants were removed from crowded sites and data were recorded. The new site was prepared prior to planting; seedlings were planted at 0.5 metre intervals along a 50 metre transect and then caged. Although the original plan was to plant out up to 105 plants into two transects over the day, things don 't always go according to plan. For example, the most vigorous tubers may not be the easiest (and quickest) to remove.

Ongoing monitoring, watering and follow-up care is necessary. The team will also research to determine pollinator identification and occurrence for potential reintroduction / translocation sites.

A total of 63 plants was moved to two new sites within the reserve, the translocation involving the assistance and expertise of many people.

With the future development of sites such as Point Danger resulting in habitat loss and degradation, having the knowledge and experience to undertake translocations and reintroductions is unfortunately becoming increasingly relevant.

Andrew thanked A.N.O.S. Vic. members for their assistance over many years with orchid recovery. Last year, recovery efforts after the Grampians fire were instrumental in assisting the protection of Caladenia versicolor. The work consisted of removing soil disturbed by the fire, and the installation of guards around emerging leaves allowed the plants to flower freely.

Searching by the A.N.O.S. Conservation Group during spring uncovered a large number of new populations of orchids within the Grampians fire area, and further work this year will be conducted on the Pterostylis chlorogramma and Paracaleana disjuncta populations that were discovered last year.