Zoologists from the University of Cambridge have developed a new technique for finding out about insect habitats, which has important implications for understanding how insects will fare if the global climate changes.

Their paper, ‘On the vapour trail of an atmospheric imprint in insects’, was published on Wednesday.

The new technique allows scientists to find out the exact humidity of the environments in which insects live. They do this by analysing water molecules in the insects’ haemolymph – their equivalent of blood. Knowledge of the insects’ preferred environment can be used to predict which species are most likely to survive in changing habitats.

The research was lead by Dr Farnon Ellwood, of Cambridge’s Zoology Department. "There is an urgent need for a better understanding of how global environmental change will affect threatened plants and animals," he said. "If we can determine the habitat preferences of individual insects, we can use this information to predict how climate change will impact on a group representing three-quarters of the Earth’s animal species."

The new technique involves looking at the atomic composition of water inside the insects. As in carbon dating, researchers gained important information from measuring the ‘heaviness’ of atoms. They examined the oxygen contained within the insects’ water molecules. There are two types of oxygen atom, one light, 16O, and one heavy, 18O. In dry conditions, the water inside the insects will evaporate, and, as the lighter water molecules will disperse first, the heavy ones will be left behind.

Insects living in dry climates where lots of evaporation takes place will therefore have more heavy oxygen than normal in their haemolymph. The opposite is true for insects living in humid conditions, where water will diffuse into the haemolymph. Since this water contains more light oxygen, these insects will have a comparatively lighter haemolymph.

Whilst it might seem easier to find out about the insect habitats from studying the areas in which insects are found, this is challenging in practice. Insects in the rainforests live high in the canopy, whilst others live in undergrowth or soil, making it difficult to study them. The new technique makes research easier because precise information about the insect habitats can be determined in a laboratory by studying the insects themselves.

The researchers who developed the technique believe that it will allow scientists to pinpoint exactly what conditions different species of insects prefer. They say, "At present, we lack a comprehensive understanding of the organization of ecosystems such as tropical forests..., which limits attempts to predict the responses of these ecosystems to climate change."

By improving understanding of how complex biological communities arise, the researchers hope that we will be more able to predict what will happen to those communities in a changing climate.