University of Jyväskylä

A different weapon against each enemy

It’s a dangerous world out there, especially if you are a small insect. Insects have thrived on our planet for hundreds of millions of years, so they must be doing something right despite all the threats to their survival. With so many predators out to get them many animals have evolved chemical defences, making themselves distasteful or even toxic. Wood tiger moths protect themselves from multiple predators using different chemical defences. Choosing the right defence can be tricky as predators come in many forms, and from many directions.

Now the researchers from the Department of Biological and Environmental Science at University of Jyväskylä have shown that one moth species, the Wood Tiger Moth, has found a clever way around this. The moth, which is brightly coloured to signal to predators that it is not to be messed with, has not one but two defensive fluids. One of them is targeted towards bird predators, who may try to catch the moth on the wing. A chemical compound in it, pyrazine, has one of the most repulsive odours known and can make the bird refrain from consuming the moth before even tasting it.  The second type of fluid works against invertebrate predators, such as ants, on the ground. This defence is particularly handy in situations where the moth cannot flee due to low temperatures, or when it is coming out of its pupa and its wings are not yet fully extended. The research, published in Proceedings of the Royal Society B: Biological Sciences on  September 27th, 2017, used a series of assays with live predators to reveal the first evidence of a single species producing separate chemical defences targeted to different predator types.

butterfly
Wood tiger moths produce two different fluids when attacked: one<br /> repels birds,<br /> while the other one deters ants. This is the first documented case of<br /> target-specific chemical defences in an insect. Photo: Bibiana Rojas

The scientists are studying this moth as part of a larger project to understand how predator-prey interactions can drive and maintain the evolution of diversity in both anti-predator defences and warning signals. Their findings highlight the need to take into account a diverse array of enemies when studying anti-predator defences, particularly invertebrates, which are some of the most abundant creatures in nature.

The work was conducted at the Centre of Excellence in Biological Interactions from the Academy of Finland.

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