Spider Venom on Apples - Natural Insecticides
Robyn Williams - Hello, I'm Robyn Williams, presenter of The Science Show on ABC Radio in Australia. It's a program similar to The Naked Scientists, but they don't let me go naked. But enough of me! Scientists in many areas are looking to the natural world for solutions to problems which in some cases have been solved already. An example is the area of insecticides. Spiders have been making molecules which kill insects for hundreds of millions of years. So why not isolate and copy these powerful molecules? This is the work of Glenn King at the University of Queensland...
Glenn King - We started thinking about this about ten years ago, and we thought, well, where could one look for molecules that would kill insects? And we decided that the best insect killers on the planet were spiders, and we figured that if anyone would get away with killing insects it had to spiders since they'd been working on it for around about 400 million years, you'd figure they'd have probably come up with a solution or two by now. And so we started looking in their venom. I think most people have a fairly poor appreciation, at least non-scientists, of what venom is.
Going into this project I mistakenly thought that spider venom might contain 10, 20, a few dozen compounds, but it turns out to be an incredible chemical cocktail of hundreds and hundreds of different components. Our job was to pick through and try and find the ones that just killed insects and had no toxicity to vertebrates. So even though some of the spiders we work with are toxic to humans, it's just one of those thousand or so compounds in there that's toxic to humans and many of the others are completely harmless, and of course they're the ones we're really interested in.
Robyn Williams - Yes, it's bad enough with all the substances in the venom, but which spiders?
Glenn King - We chose the Australian funnel-web spider, which may sound like an odd choice given it is one of the four deadly spiders in the world. Again, I should put this in context that there are about 40,000 characterised spiders now, there's a website you can go to and look up all the names of them all, and of those 40,000 there are only four families of spiders that are potentially lethal to humans; that's our own funnel-web spider, the red back spider, the recluse spider in North America and the Brazilian armed spider in Brazil. All other spiders are completely harmless. They might give you a nasty bite but they're not going to kill you. So what that tells you of these thousands of compounds in these tens of thousands of spiders, most of them are going to kill insects and be harmless to vertebrates.
A group at Deakin Research led by Merlin Howden about ten years ago had looked at a whole bunch of Australian spider venoms and said; which one of those is best at killing a really refractory agricultural pest, the cotton bole worm, which most people have probably heard of. It turned out funnel-web spider venom was the best, and so we knew there were good compounds in there and that was the reason we chose that spider.
Robyn Williams - Narrowing it down from all the hundreds of ingredients, how did you do that?
Glenn King - We have to fractionate out...we use a process called chromatography. It turns out that that process is not enough to fractionate out what we now know are 500 to 1,000 compounds. So what we've done now is gone back and made DNA libraries from the venom glands so we can look at the DNA and sequence the whole profile of all the compounds that are in there, and then we just make those compounds in bacteria and test them individually. And so from these 1,000 or so compounds we've narrowed it down to only 10 or 20 that we're really interested in.
Robyn Williams - And what did you do with that 10 or 20? Get insects and do a trial run, see how they react?
Glenn King - We did, and the good thing is you don't need ethics approval to kill insects, which makes the process a lot easier.
Robyn Williams - It will come!
Glenn King - Yes, probably. We actually usually use house flies or crickets that we can just buy from the pet shop and we inject compounds into those and see what effects they have.
Robyn Williams - And is it effective?
Glenn King - Yes, it is, it's very effective. The compounds that we're using as are as effective as any like compounds that people have purified from other venoms, whether they be scorpions or cone snails or anything else. We were thinking originally that these things are peptides, so they're little tiny proteins, so what we like about them is they're natural compounds. We were concerned initially that these natural compounds weren't going to be orally available to insects, so if they ingested them they'd get broken down in the digestive system of the insects and they wouldn't work. But it turns out that a lot of these are quite potent when insects ingest them, and so we think these natural compounds could be very effective insecticides in their own right.
Robyn Williams - What happens when you actually use these? Because obviously there are some insects which you want to preserve like dragonflies and butterflies and many others, are they selective in that way?
Glenn King - There's some selectivity, and so you may want to choose your particular compound for your particular insect that you're trying to kill. Another way around it is to...because these things are just proteins, they could be used to make genetically modified crops, and then the only insects that would be affected would be anything that preyed on those crops, so that's one way of confining the range of insects that are targeted.
Robyn Williams - And then there's the problem of human sensitivity, I suppose, because whatever you said about insecticide, if I see a wonderful piece of fruit there and I think it's got the residues of spider poison on it...
Glenn King - Yes, and that's certainly an issue we're going to have to deal with in terms of commercialisation and what we're going to have to get people to realise, as I said, is that spiders for the most part are completely harmless to humans and we've injected these things into a whole bunch of different vertebrates and they run around doing what they normally do without any ill-effects. So I agree that's an issue that the marketing people will have to deal with.
Robyn Williams - But the commercialisation, has it reached that far yet? Have you got some sort of spider venom, one that you're offering to companies?
Glenn King - Not yet. So while I was in the United States, from which I just returned recently, we spent at a company from the university I was at based on this research. The application that we're thinking of first of all is for controlling ecto-parasites, and by that I mean fleas, mosquitos and ticks on pets. Insecticides on pets are actually very harmful to young children, and so it would be nice to have something that was more environmentally friendly, or at least that kids were less sensitive to.
Robyn Williams - What about the anopheles mosquito?
Glenn King - Yes, these things are really, really effective against mosquitos. In fact, mosquitos and flies are the things they kill best, and again they're orally active against mosquitos, we've been testing it against one that's really important in Queensland Aedes aegypti which is the dengue vector and carries a number of other nasty diseases. It's very effective against that, and so we think there could be applications in terms of treatment of environmental situations to control mosquitos.
Robyn Williams - I can just imagine a factory full of funnel-webs milked like crazy.
Glenn King - Yes, people often conjure up that image in their mind but the truth of the matter is we make these things in bacteria so we don't even have any funnel-webs in the lab most of the time.
Robyn Williams - Well, that's okay then. So next time you eat an apple, think of the spiders who kept it in such good condition for you!