Sex can cloud the senses. In a state of excitement, many succumb to false promises. This is also the case for the thynnine wasp male Neozeleboria cryptoides, who, seduced by the appearance and odour of the Australian orchid, Chilogottis trapeziformis, gives up his search for a female of his species. For the orchid this successful deception is vital to reproduction, because the wasps are responsible for its pollination. Diverse ethological and chemical investigations have shown that the enticement of specific pollinators depends on volatile compounds that the orchid emits (1). But what are these substances? Together with other researchers, Florian Schiestl from ETH's Geobotanical Institute applied this question to Chiloglottis. During their studies they discovered an unknown natural substance. Their study was published last week in "Science" magazine (2).

Extracts from flowers and heads of female wasps

In order to analyse the specific compounds that attract the male thynnine wasp, the researchers used labella extracts from the orchid's blossom and head extracts of female wasps. They separated the substances by means of gas chromatography. “Then we tested the biological activity of the substances with a very special test, using an analysis called an electroantennographic detection, by which the antennae of male wasps were separated," Schiestl explains. The antennae can be used for roughly an hour after separation because the smell neurones stay active for that long. What the team measured were changes in tension that occur when the cells detect a connection. And, indeed, only one single component proved to be active, which means that the active compound in both orchid and wasp is identical.

ETH biologist Florian Paul Schiestl, who, together with colleagues, has discovered a new natural substance. large

Seduced: A male thynnine wasp landing on a Chilogottis trapeziformis orchid. (Picture: F. Schiestl) large

A new substance: Chiloglottone

The researchers now had the attractive substance but they did not know its chemical composition. A number of spectrum analyses were carried out and comparisons with chemically synthesised substances. It transpired that the substance they had discovered was 2-Ethyl-5-Propylcyclohexoan-1-,3-dion, a substance which not only has never been described up until now but which fits no known class of natural substances. They called the new substance Chiloglottone. "The substance was first detected in the genus Chiloglottis," is the reason Schiestl gives for honouring the orchid. The "one" in the name stands for two ketone groups, which characterise the substance.

Why they were deceived

Chiloglottone, however, still had to undergo a hard test, namely whether it really attracts male wasps. "Such a test is very important. Because there are substances that are discernible, but which do not trigger a behavioural reaction," explains Schiestl. To test this the group of researchers carried out a field test in which they offered both synthetic and natural Chiloglottone from wasps and orchids, to free-living male wasps. The substance, regardless of which source, attracted the male wasps. The artificial substance proved to be as effective as its natural competitors. This was further proof that the team was dealing with one and the same substance in all three cases. It's no wonder, therefore, that the male wasps were led astray.

Specialisation and speciation

Could it be that perfect deception via odorous substances exists for other types of orchids? Schiestl thinks this is probable and believes that more new substances will be found. What the biologists finds so fascinating in his research is not only the discovery of new substances but the fact that such highly specialised development occurs. The dependence of Chiloglottis on one substance limits its evolutionary flexibility to a considerable extent. Nevertheless, such a specialisation can also have advantages because the waste of pollen is kept to a minimum. Whether or not Schiestl's hypothesis proves to be correct, it is not going to stop him continuing his research on how specific attraction works. Once a number of closely related species are analysed a better understanding can be had of how populations become reproductively isolated owing to a specialised pollination mechanism, and how new species then evolve.