Passing gas

Improvements in sampling techniques and mass spectrometry in the last 20 years have revealed that plants emit a wide range of volatile chemicals such as methanol, acetone, formaldehyde, plus a host of terpenes, phenylpropanoids, benzenoids, and many more. One key question is whether these chemicals perform a function or are the plants just "passing gas" by emitting compounds that are by-products of essential processes?

In the last decade or so the emitted compounds have been shown to both deter herbivores themselves and attract predatory and parasitic species that attack herbivores.

A recent research report shows that herbivore-induced volatile organic compounds elicit a defensive response in undamaged plants (or parts of plants) under natural conditions, and they function as an external signal for within-plant communication.

On a related topic, the monarch butterflies that you sometimes see around are not only able to cope with the toxic compounds found in their host plants, milkweeds, but they store them making the larvae and adults distasteful and toxic to their predators.

This time last year: Some like it hot