An Orchidist's Miscellany

POLLINATORS 

 The pollinators of orchids have played a major role in their evolution. Orchids are thought to have been highly pollinator-oriented even from the earliest stages of their development. Other plant families had similar orientation, but it is thought some special breakthrough occurred allowing specialisation of orchid flowers with rapid evolution based on the pollinators. The complex pollinator mechanisms which evolved reduced the possibility of natural hybridisation with its consequent reblending of characters in the development of the species.

Van der Pijl and Dodson consider some 86% of orchids are pollinated by various types of insects. The pollinators are listed as follows:-

Wasps and bees 60%
Moths 8%
Butterflies 3%

Flies

15%
TOTAL INSECTS 86%
Birds 3%
Mixed agents 8%
Autogamous 3%
  100%

The primary characteristics of orchids pollinated by the various agents can be briefly summarised as follows:

1. Bee and wasp pollinated orchids open during the day, when these insects are mostly active. The flowers generally produce odours pleasant to us, as these insects have a highly developed sense of taste and smell. The flowers also generally have bright colours in the violet, blue, green and yellow visible light spectrum, which is attractive to these insects. They cannot see the red colours, although do react to ultraviolet. A well developed 'lip' landing platform with well developed lines or keels leading to the nectaries are present

2. Moths and butterflies are generally attracted to nectar producing flowers. Moth pollinated flowers generally open at night, some even close during the day. They produce strong odours at night which are musky-sweet or vegetable-like.. The lip (landing platform) tends to be either turned back out of the way, or turned upwards. Colours are commonly white, creamy, or even green, to show up at night. Abundant nectar is produced, often hidden in deep cavities or tubes.
Butterflies fly during the day, and are attracted by bright coloured flowers having fresh agreeable fragrances. As they are not strong flyers, they generally have well developed landing platforms on the flowers they pollinate. Abundant nectar is usually produced in deep cavities.

3. Bird flowers are generally highly coloured, with red predominating. There is usually little fragrance produced as birds have little sense of smell. The flowers are also often pendant, as the birds normally do not land on the flower, but hover in front. Abundant nectar in deep cavities is characteristically produced by bird pollinated flowers.

4. Flies may be attracted by food sources, or may be attracted by deception. Flies which seek food are usually attracted by flowers having shallow nectaries, sweet odours and an open shape. Many insects are, however, looking for decaying substances, either to lay their eggs, or to obtain food. Some flowers imitate these substances, producing un- attractive odours to humans, often coloured like rotting meat or other foul substances. These flowers often have trap devices to hold the pollinator, with various, often complex, attracting devices. Some fly pollinated flowers have returned to a radial pattern (e.g. Cirrhopetalum).

5. Other agents exist, but are not significant with respect to the orchid family overall.

The principal pollinators of the following genera occur (refer to Van der Pijl and Dodson for full list):

Anguloa

bee

....

Barkeria

bee

Brassia

wasp

Catasetum

bee

Cattleya

bee

Cirrhopetalum

fly

Coryanthes

bee

Corybas

fly

Cymbidium

bee/wasp

Dendrobium

bee/fly/bird/wasp

Disa

fly/buttefly

Epidendrum

bird/moth/butterfly

Haemaria

butterfly

Laelia

bird/bee

Lycaste

bee

Masdevallia

fly/bird

Maxillaria

bee

Miltonia

bee

Odontogiossum

bee

Oncidiurn

bee

Pterostylis

fly

Paphiopedilum

fly/bee

The relationship of orchids to their insect pollinators is fascinating, and it can be an interesting exercise looking at a flower and imagining how it is pollinated, and by what


Site established 9th May 1998