New laboratory method moves chemical ecology in the right direction

clDid you know insects are masters of communication? Insects send and receive information through  many different avenues. While honeybees use the waggle dance to communicate with one another – some species of leafhopper prefer to chat through vibrations made by drumming their bodies against leaves and twigs. While abdomen-waggling and tapping are good fun, perhaps the most common way that insects communicate is through sending and receiving semiochemicals.

Semiochemicals are chemical signals that mediate communication between organisms. They are organic compounds, meaning they are composed chiefly of carbon and hydrogen, though other elements including oxygen, nitrogen, sulphur, and phosphorus can also be important components. Semiochemicals are often complex molecules, and within the insect world can be lumped into two main categories: volatiles, and contact hydrocarbons.

Volatile compounds are what many insects use to communicate over long distances. These are chemical signals that are sent into the air, or water to be received by another insect. Often female insects will produce pheromones, which will attract recipient male insects looking to mate. Other times these chemicals send a message that bring together large groups of the same species in aggregations.  These chemicals have proven to be incredibly useful within integrated pest management strategies, and have been well studied in comparison to the other principal type of insect chemical signals: contact hydrocarbons.

Contact hydrocarbons are part of a complex layer that envelopes the insect. This layer known as the cuticle. The primary function of the cuticle is to waterproof the insect, however individual components of the cuticle act also act as signals that mediate different behavioural, and physiological changes within an insect. By understanding more about the identity of these hydrocarbons within the insect cuticle, we can in turn learn an impressive amount about the ecology of a species.

When it comes to identifying organic chemicals,  chemists have many useful tricks up their sleeves. However, contact hydrocarbons have not been so easy to identify. Firstly, there are many complex molecules within an insect cuticle, which makes it challenging to isolate a particular compound of interest. The second challenge is associated with the most appropriate analytical tool used to isolate these chemicals – high pressure liquid chromatography (HPLC). While HPLC has the capabilities to separate these compounds, it is limited by sensitivity of detection.

A group of researchers from University of California, Riverside have come together to work around this problem. In a paper published in the Proceedings of the National Academy of Science , the team describes a new combination of laboratory techniques that can be used to isolate and identify these compounds.

The team did this by looking at a randomly selected group of insects: 20 different species from nine separate insect orders. In total, the team isolated 36 separate hydrocarbons from these insects. Surprisingly, all compounds had something in common: their chirality.

Chiral molecules are chemicals with identical composition, but are non-super-imposable. These pairs are called stereoisomers and are best understood by picturing a pair of human hands. If you hold your hands palms-together, it’s clear that they are a mirrored reflection of one another. Imagine trying to place your left hand into a right-handed glove. There is no way you could place your hand comfortably within a glove intended for the other hand.

This is analogous in the biological world. While two hydrocarbons can have exactly the same structural components, different stereoisomers of a hydrocarbon send two very different signals to a recipient. In the case of this new work, the team discovered that every compound isolated was oriented in the ‘right’ direction . For some reason, production of right oriented cuticular hydrocarbons seems to be well conserved within the insects.

Now that a method has been outlined for isolating and identifying cuticular hydrocarbons, there will undoubtedly be a fantastic movement forward to use this knowledge to our benefit.  After identifying what the particular compounds are, scientists can then research how insects respond to these chemicals. We can use this knowledge to: fight invasive species, introduce targeted pest management strategies, and answer interesting questions about the natural world around us. This is truly a significant step in the right direction.

Reference:
Bello, J. E., McElfresh, J. S., & Millar, J. G. (2015). Isolation and determination of absolute configurations of insect-produced methyl-branched hydrocarbons. Proceedings of the National Academy of Sciences, 2014, 201417605. doi:10.1073/pnas.1417605112

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