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Tarantula venom to kill cotton pests

Toxic tarantulas Chemicals from the venom of the Australian Tarantula spider could one day be sprayed on, or engineered into, cotton and other crops to keep pests at bay.

Biochemist Professor Glenn King, from the University of Queensland, and colleagues, report their findings today in the journal PLOS ONE.

"It has been assumed that spider-venom peptides are not orally active and are therefore unlikely to be useful insecticides," write King and colleagues.

"Contrary to this dogma, we show that it is possible to isolate spider-venom peptides with high levels of oral insecticidal activity."

Development of pest resistance to existing chemical insecticides is a major problem facing agriculture.

One approach has been to turn to nature to find new chemicals that could kill pests.

For example, cotton crops have been sprayed with, or engineered to express, the bacterial Bt toxin.

Spiders are another natural inspiration for insecticides. After all, says King, "they're the best insect killers on the planet".

But the question has always been whether eating the chemical would kill insects.

Although spiders have been killing insects with their venom for over 250 million years, there has been no evolutionary selection pressure for venom toxins to have oral activity since they are injected into prey and predators via a hypodermic needle-like fang.

Until now, no one had ever tested whether venom toxins were orally active.

King and colleagues extracted peptides from the venom of the Australian tarantula (Selenotypus plumpies) and fed them to a number of insects.

"We found that they were orally active and that was the exciting thing," says King.

The current paper reports on one of five newly-discoverd peptides, called OAIP-1, which the researchers found was able to kill cotton bollworm (Helicoverpa armigera) with a potency similar to that of the synthetic insecticide imidacloprid.

The peptide was also active against mealworms, which attack stored grains.

Such pests reduce global crop yields by 10 - 14 per cent annually and damage 9-20 per cent of stored food crops.

Stacking genes

King says the aim is to use gene technology rather than farming tarantulas to produce new insecticides.

Insecticides that can be sprayed on crops could be produced using bacteria or yeast in fermentation tanks. Alternatively, insecticidal genes from the spider could be engineered into crops, in the same way Bt toxin genes have been.

"One of the nice things is that Bt and these peptides have very different modes of action," says King.

He says this means it would be possible to engineer crop plants that have both Bt and spider venom genes "stacked" inside them, creating a double hurdle to the development of resistance.

King says the new toxins are also likely to be synergistic with Bt, since the latter punches holes in the gut which could allow the venom peptide to diffuse out into the body more easily.

He says the spider toxins have much broader activity than Bt, which means they kill a greater range of insects.

"That can be good and bad of course," adds King.

He says before the peptides can be used in agriculture it will be important to confirm they are not toxic to vertebrates or beneficial insects.

The five new peptides were found by team member, Margaret Hardy, as part of her PhD. The research was funded by an ARC discovery grant, and has since led to a linkage grant with an agricultural chemical company, says King.

Spider analgesics

King is also interested in developing new oral analgesic drugs that block sodium channels in human cells, known to be involved in pain sensation.

"The fact that we've shown these things can cross the insect gut, suggests they can probably cross the human gut as well," he says.

King emphasises that whereas most snakes are venomous to humans, most spiders are not.

"Almost all of the large tarantulas are completely harmless to humans, which is why they are commonly kept as pets," he says.