Science Interviews


Sun, 13th Nov 2005

How Caterpillars Fight Back Against Parasites

Professor Elizabeth Bernays, University of Arizona

Part of the show Parasites, Hookworms and Allergies

Kat - We've been talking about human parasites, but you're going to talk about caterpillar parasites. What have you been looking at?

Elizabeth - I've been looking at caterpillars that live in Southern Arizona, and they get parasites from flies that lay their eggs on the outside of the caterpillar. The eggs hatch, the parasites dig in and eat out the entire caterpillar.

Kat - That sounds really horrible. What do caterpillars do about this?

Elizabeth - One thing that they do is to eat a certain plant that contains a chemical that protects them a bit from the parasites. If they eat enough of this chemical it will kill some of these maggots and allow the caterpillar to continue living.

Kat - How do the caterpillars know which plants to eat?

Elizabeth - That's a good questions and that's one of the things that I've been studying. They have a special taste bud that's sensitive to some of the chemicals in the plant. The chemicals are toxic and taste very bitter to humans, but caterpillars love them. This is a good adaptation because when they come across a plant with these chemicals, they like to eat that plant. One of the problems is that they eat a lot of different plants. When they have parasites, their taste for this chemical gets stronger and stronger. This makes their taste buds go wild when they taste this chemical. This makes sure that they eat a lot of that chemical.

Kat - So they acquire a taste for it when they need it.

Elizabeth - Well they have a taste for it but it becomes much more sensitive when they need it.

Kat - How did you find this out? How did you test for this?

Elizabeth - Well I've been working on the taste buds of these caterpillars for some time, and found that they have one that's sensitive to sugar, and one that's sensitive to bitter substances. And then I found that there was one sensitive to these chemicals. This lead me to think that they must be good for them. Just by chance, I found that the sensitivity varied a lot. We did a test that showed that when they have parasites, they get more sensitive. We've also showed that the caterpillars that eat these chemicals survive much better.

Kat - Do you think that anything like this happens in other animals?

Elizabeth - We haven't been able to find it any other stories of animal taste, so we don't really know how prominent it is. There's no suggestion of it in humans, but maybe we just aren't looking at the right things. Maybe it's just that insects are different and their taste buds vary more depending on what they need.

Sarah - Are the chemicals good for the creatures that eat the caterpillars?

Elizabeth - The caterpillars that prey on them have special mechanisms to stop them from being poisonous. But the chemicals do protect them from parasites and predators. One other interesting detail is that the chemicals that usually taste bitter to them don't bother caterpillars at all when they have parasites. That makes them eat other plants with other toxins, and that also helps to kill some of the parasites.


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