This week’s blog, Part One of Two Parts, is quoted directly from the introductory chapter (Pages 2&3) Orchid Pollinators of Victoria 4th Edition, 2016, Rudie Kuiter. Over the years of photographing orchids and their pollinators, Rudie and his team have been discovering much of the hidden world of orchid pollinators. In this first section he highlights the fallacy of the “one orchid-one pollinator” as well as touching briefly on the vast difference between the insects and their role in the ecosystem.
Click here for Part Two
Amongst flowering plants, orchids have evolved in their own special reproductive ways. Their pollen is massed as waxy packages, pollinia, unlike like (sic) other flowers that produce masses of fine pollen grains that mostly go astray. The pollinia are relatively heavy and the usually small creatures need to be strong fliers for cross pollination (see image below). Orchids evolved with amazing strategies to attract specific carriers in order to transfer pollen between flowers of their species only, and in this way eliminating the need to produce great quantities. Various insects, many moths, bees and even birds have been documented as pollinators of orchids around the world (v.d. Cingel, 2001). A number of uniquely different examples of orchids attracting insects for their pollination evolved in Australia, especially in the more temperate southern zones originating from Gondwana times. With very few exceptions the Victorian orchids are terrestrial, ground-dwellers, that rely on small insects such as fungus-gnats, native bees, wasps, ants and many attract only the males by sexual deception. In the case no pollinators visits, many species may self-pollinate as a back up.
When taking an interest in orchids it seems difficult enough to identify some species. Usually one looks and admires the amazing flowers that may resemble an insect and can be difficult to recognise as a flower at first. An insect on a flower may be thought of something that spoils a picture – until taking an interest in the visitor!
Hoverfly on Caladenia rigida (syn Arachnorchis rigida)
I first learned about the orchid pollinators in Orchids of South Australia by Bates & Weber, 1990, an excellent book by today’s standard, but few were seen over the years by just being there at the right time when photographing orchids. During preparation of the book on Caladenia spider-orchids, certain issues developed from questionable statements made in scientific papers about wasp-pollinators. Of particular concern was about the one-to-one relationship – how only one wasp-species would be involved with only one spider-orchid species – and suggesting populations that were thought to represent the same species comprised different taxa if not pollinated by the same wasp-species. A very different story emerged when monitoring the local spider-orchid populations to find the answers and it became clear that there was much more to it. A site in Wonthaggi with a very large colony of Caladenia dilatata proved to be perfect for this study and also to photograph pollinators as it produces flowers for about four months. It was found that a local wasp-pollinator species typically flies for a little over one month, thus this need to be investigated further. Scientific publications on wasp-pollinators were generally based on short-term experiments, and usually employing baiting methods – moving flowers and often taking them to different sites. Responses included unnatural behaviour or attracting sibling wasps at a non-local site. It is certainly true that a particular flower may attract only one species of wasp a t a locality and a certain time in the season, but this reflects a very small part of the picture. It can be different in the long-term, at certain localities or with a season.
The main study site was in coastal dunes, where in a very large population of Caladenia dilatata produced flowers for over four months from September, and under favourable Summer-conditions into January. At least three congeneric (belonging to the same genus) thynniid wasps species were involved in this population. The flying times were up to about 6 weeks for each wasp species, that were separated or slightly overlapping. The flowering times in other populations of C. dilatata in Wonthaggi and Wilsons Promontory were usually about one month in each, and at the corresponding times to the study site the wasps visiting were the same species. A close sibling C. parva in the Wonthaggi heathland habitats and early flowering C. dilatata were pollinated by the same species, but the later flowering C. tentaculata by a thynniid wasp of the different genus.
Hoverfly with pollinia
Whilst a flower may attract only one wasp species, the kairomones (chemical omitted by the orchid to attract a pollinator) of a species may vary between flowers within in a population or when allopatric (growing in different geographical regions), just like colour or morphology. Variations maybe in relation to locality, weather conditions, or ground chemistry and available pollinator. Pollinators may evolve over time, but adaptions usually require many seasons and this would vary with location. The observations made over several seasons suggest that more than one congeneric insect is involved in pollination depending on local or seasonal conditions, especially after a long drought. Chiloglottis gunnii populations in Langwarrin were checked for pollinators since a decade-long drought and no action was seen for many seasons. When wasps finally made an appearance they comprised different taxa of Neozeleboria the first season, but only one became the common and principal pollinator the following seasons. Thynniid wasps are very localised as females lack wings and rely on the males to carry them around during copulation and to provide food. It limits their travelling and their homing range may comprise just a few hundred metres. Thynniid wasp are very vulnerable in small reserves isolated by land-clearing, and certain species have gone locally extinct due to conducting burns. Insects form a crucial and fundamental part of an ecosystem, but their importance is never considered in the planned burning, showing a complete lack of understanding by people in charge. So little is known of ecosystem’s foundations, but controlled burning continues – ruining precious habitats. Orchid species failing to produce seed pods is an indication that pollinators were absent, probably gone locally extinct. Orchid species that have a sexual association with thynniid wasp pollinators are localised and usually have geographically variable flowers. The situation is different with Cryptostylis spp. And their pollinating male wasp Lissopimpla excelsa, as females are a strong flyers. The flowers of Cryptostylis are geographically uniform in each species and the wasp is widespread. Both sexes are very distinctive in colour that show no variation. They are active over Spring and Summer and are great travellers.
To be continued …