Science Show

Jerome Rozen studies bees. The 20,000 species are found in all continents except Antarctica. They are abundant in arid and Mediterranean climates. Jerome Rozen studies solitary bees and parasitic bees rather than social bees. He describes their behaviour and how they treat the eggs and larvae of the host bees.

Transcript

Robyn Williams: Darwin made much of the cruelty in nature; parasitic wasps whose larvae consume caterpillars from the inside-out, organ by organ. Bees too can be parasitic. Many of them like cuckoos, taking over the nests of other species. Jerry Rozen has studied them for decades.

Jerome Rozen: I've been studying bees certainly for 60 years.

Robyn Williams: Sixty?

Jerome Rozen: Six-zero.

Robyn Williams: Where do you go to look at them?

Jerome Rozen: I go all over the world to look at them. Bees are found in almost all continents except Antarctica. But there are most abundant in arid parts of the world, in Mediterranean climates.

Robyn Williams: And why are you concentrating on parasitic bees?

Jerome Rozen: I don't necessary concentrate on parasitic bees, I also study solitary bees. What I don't do is to study social bees because there are so many other people working on social bees that I like to find a niche that needs to be explored, and there are a lot of them.

Robyn Williams: In my innocence I thought that this was a completely exceptional thing. What sort of percentage, would you say, of bee species are parasitic?

Jerome Rozen: I've been told that there are about 15% parasitic. There are roughly 20,000 species of bees in the world, so everyone can do the mathematics as well as I. So there are a lot of parasitic bees.

Robyn Williams: It's elaborate behaviour, isn't it, where you kind of set out to take over someone else's nest. How does it work, what do they do? Same as cuckoos?

Jerome Rozen: Not the same as birds but there's some similarities. What they're really doing is looking for a place where they can deposit an egg and where the egg can hatch and be fed. The females don't collect food for their young, what they're doing is looking for somebody else's food, and so they look for the nest of another bee. They may be quite specific. A parasitic bee may be restricted to only one genus of potential host bee. The problem arises that they have to be able to identify the nest and they probably can't identify the nests of all different kinds of bees. Different species nest in different situations, so they're looking for a very specific nest, and then they deposit the egg within the brood chamber within that nest.

The problem arises that if a parasitic bee has her egg in the nest and the host bee also has her egg in the nest, there's only enough food for one surviving, so one larva has got to be eliminated and that's usually the larva the host bee has killed or sometimes the egg of the host bee is removed or killed one way or another. How that is done depends upon the species of the parasitic bee. Some parasitic bees, the female invading the nest merely removed the egg of the host bee, but sometimes the parasite bee is put into the nest before the host bee has put her egg in the nest, in which case it's up to the parasite larva to have the equipment to assassinate the host egg, and they do that usually with their mandibles.

Robyn Williams: It reminds me to some extent of the cuckoo birds. I think that the parent chucks one egg out so that if the poor host birds can count they won't notice any difference, and of course when the cuckoo bird is born it gets rid of the rest of them perhaps. But what you're talking about is very low numbers, so it's just one other egg and one other rival.

Jerome Rozen: That's almost always the case, although I do know of one interesting case where the host bee is a very large bee and the literature indicates that a number of parasite eggs can be deposited in there and they all survive. The interesting thing is that they don't attack one another in those cases. Another situation is if two parasites find a nest and there's enough food for only one larva to survive, the parasites will battle one another. In this one case you can open up the nest and find five or six cocoons in there, each one containing a developing parasite.

Robyn Williams: I suppose it doesn't really take place in the big colonies because the defences, I would imagine, are terribly well organised and they would be knocked off very quickly.

Jerome Rozen: The hosts of cleptoparasitic bees are always solitary bees. A solitary bee, it has only one female to a nest, she is not assisted by her offspring in provisioning the nest or defending the nest or anything else, she builds the nest, she deposits all the eggs, collects all the food intended for each of her offspring, and when she's through, she dies.

Robyn Williams: So there's no onlooking collection of older bees looking down.

Jerome Rozen: That's right, there's no mass of bees as you find with honey bees and bumblebees. Those are social bees and they have these large colonies, one queen and many, many workers which are neuter females that assist in provisioning and building the nest.

Robyn Williams: It must be a very successful operation if it's 15% of the species.

Jerome Rozen: Yes, it's happened time and time again. Of course the interesting thing is that if the parasitic bees were very successful they would soon eliminate all the host bees, in which case there would be no parasitic bees. So a balance is achieved one way or another, which brings up a very interesting situation; how is this balance maintained? If a parasite is too successful it eliminates itself in the long run, and that is not beneficial for the parasite.

Robyn Williams: Indeed. Where are you taking this quest next?

Jerome Rozen: Well, the place I'm going next is actually at the end of this week I'm going to go to Costa Rica to look at a bee that occurs in the tropics of the New World. It's a very handsome blue metallic tinted bee that attacks the nest of a solitary bee that nests right along very close to the shore as a matter of fact, in Costa Rica. It's a bee that, however, is found throughout the tropical part of the New World.

Guests

Jerome Rozen
Curator Division of Invertebrate Zoology, American Museum of Natural History, New York NY USA
http://www.amnh.org/science/divisions/invertzoo/bio.php?scientist=rozen

Presenter

Robyn Williams

Producer

David Fisher

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