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I've been a Canberran since moving here from Adelaide on the first day of 1980. I now live in suburban Duffy with my partner Louise Maher, ABC 666 radio and on-line journalist. Among my early memories is following Sleepy Lizards (Shinglebacks) around the paddocks north of Adelaide, guarded by the faithful bull terrier. I have always been passionate about the natural world, trying to understand how it works, how the nature of Australia came to be, and sharing those understandings. My especial passions are birds, orchids and mammals. For much of my life I have been a full-time naturalist, running bush tours, writing books etc, doing consultancies, presenting a regular radio slot on local ABC, chairing a government environment advisory committee and running adult education classes. Recently I have eased back somewhat, but am still writing, teaching, doing some radio work and running overseas tours - as part of my fascination with our Gondwanan origins I've been running tours to South America for the past decade. I was awarded the Australian Plants Society Award in 2001 and the Australian Natural History Medallion in 2006, both for services to education and conservation.

Wednesday, 28 October 2015

Leaf Beetles and Mobile Homes

I had no intention of talking about leaf beetles today - indeed I scarcely knew anything about them and the idea had never occurred to me. Until Sunday.

On Sunday I was walking with some like-minded people along a quiet road in the Tallaganda Ranges a little to the east of Canberra. The Tallagandas contain some beautiful wet eucalypt forest, a reasonable proportion of which has now been preserved from the creeping blight of exotic pine plantations and dedicated as Tallaganda National Park.
Eucalyptus obliqua, E. viminalis and Fishbone Ferns Blechnum spp., Tallaganda NP.
On the road we found a busy crowd of odd-looking little animals, seemingly in mud-like shells, demolishing a eucalypt leaf - I was at a complete loss to explain them, to my embarrassment. There wasn't much left of their leaf, but I was concerned for their safety on the road, quiet though it was, and tried to move them and the leaf to the edge of the road. They were much more active than they first seemed however and all tumbled off to the side and proved impossible to move without risking damage to them.
A very odd little gathering!
Back in Canberra I consulted Kim Pullen, an entomologist with CSIRO (for those outside Australia, this is the Commonwealth Scientific and Industrial Research Organisation, an icon of Australian research, though shamefully starved of funds by recent governments). He put me firmly on the right track, on which I've since done a little more of my own research, though readily available information isn't plentiful.

However I think I've got enough to share a little story which I found fascinating. Our little characters are leaf beetle larvae, Family Chrysomelidae, subfamily Cryptocephalinae. Normally we don't worry too much about sub-families for day to day use, but when species numbers are as high as they are in insect families, and notably among beetles, it is a practical necessity. As a case in point, there are some 700 species of Cryptocephalines in Australia alone. 

First, a little background (bearing in mind I claim no expertise in matters invertebrate). The leaf beetles, Chrysomelidae, contain at least 3000 species in Australia, in more than 250 genera. Both adults and larvae specialise in eating plant tissue, including, as you'd expect in Australia, both eucalypt and acacia leaves.
A leaf beetle, probably of the same subfamily as our subjects, effectively
chewing an Eremophila leaf, Whyalla Conservation Park, South Australia.
The best-known are probably the numerous species of the genus Paropsis, or tortoise beetles. A major part of the secret to their success is in being one of the few groups of organisms in the world which have managed to unravel the chemical binding of proteins to the tannins in eucalypt leaves. These greatly limit the availability of essential nitrogen to those munching on them, making them pretty unattractive to most leaf-eaters.
Tortoise beetles - larvae above, adult below - demonstrating their disdain for the chemical
defences in eucalypt leaves. The larvae, moreover, exude deadly hydrogen cyanide from glands in
their rear ends - enough to kill a meat ant outright.
 
Another Chrysomelid is well-known to orchid growers - the Orchid Beetle Stethopachys formosa (subfamily Criocerinae) specialises in eating orchid flowers, notably the summer flowering hyacinth orchids, Dipodium spp. They really appreciate the nice warm conditions in greenhouses!
Orchid beetle on lunch - Dipodium punctatum, Rosedale, south coast New South Wales.
So, what's the story of our little friends on the Tallaganda road? Kim Pullen tells me that the only way to even allocate them to a genus would be to raise them to adulthood, but my fostering skills are not up that, even if I was willing to rip them from their friends and family. As the the female beetle laid each egg on the ground, she caught it in the 'foot' of her rear legs and coated it in droppings, which are composed of eucalypt leaf material. When the egg hatched, the little beetle larva broke a hole at the front of the case and with the assistance of its front 'legs' moves about the forest floor eating the litter. I am told by Kim that Dr Chris Reid of the Australian Museum in Sydney, an expert on Chrysomelids, considers them an important player in the cycle of litter breakdown in eucalypt forests 

An enlarged view of a section of the above photo shows some of the larvae protruding from their mobile homes. These homes provide both physical protection and effective camouflage in the litter.
As they grow they add to the case with their own droppings, and when the time comes they pupate within it, eventually emerging as an adult beetles.

A small story in the bigger scheme of things, but it fascinated me and I hope you found something of interest here too.

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6 comments:

Harvey Perkins said...

You might just want to change the first two instances where you use the family name from Chrysopteridae to Chrysomelidae... But a fascinating story. Must admit I haven't come across larvae of this sort before.

Harvey Perkins said...

And just a question. If they grow their 'shell' by addition of faecal material, do they have to exit their shells in order to do so. Or might they transfer it to their mouth parts in order to apply it to the growing edge? I've no reason to question you, but it would be much more easy to imagine the process if the shell was composed of regurgitated or masticated material rather than faecal. ???

Susan said...

Here we have Scarlet Lily Beetle Lilioceris lilii. They are Chrysomelidae Criocerinae. The adults are beautiful shiny scarlet and black creatures. The larvae cover themselves in their own excrement, which gives them a dark moist irregular look, like a bit of mud or a bird dropping.

I've never encountered the ones you describe in your blog post, in their rather neat little capsules.

Ian Fraser said...

Thanks Harvey - goodness knows from where I dreamed up Chrysopteridae, but I have fixed it now. Re your other very pertinent observation, don't worry about questioning me; that's always worth doing and especially in this case. There seems no doubt that the original casing, from the mother, is of faecal material; as for the later additions I've read only that the larva supplements it, and your suggestion seems very plausible to me. It may be that we don't know that answer.

Susan, thanks for that too. I've looked up your Scarlet Lily Beetle and it really is a gem!

Simon Grove said...

Fascinating article. Those larvae look like a species of Cadmus, e.g. the delightfully named Cadmus excrementarius. Unusal for a leaf-beetle in feeding on fallen eucalypt leaves rather than fresh foliage.

Ian Fraser said...

Thanks for that Simon. I've come across Cadmus, but not the marvellous C. excrementarius! I fully agree with you re the unusual nature of them living on fallen leaves. I was intrigued to notice however that ours were eating green leaves and am not sure how they came by them. I was also puzzled that they were on the road. Ah mysteries, to keep us thinking!