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23 October 1998 |
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In a pre-emptive strike on the devastating silverleaf whitefly that can cause millions of dollars in crop damage, CSIRO scientists have discovered tiny Australian wasps that could help wipe out populations of the pest.
The silverleaf whitefly was accidentally introduced from the USA to New South Wales and Queensland in 1994 in ornamental plants and has since spread from northern NSW to Cooktown, Adelaide and Perth.
It causes crop damage to cotton, tomatoes, melons, flowering plants and vegetable crops, and is already troubling nurseries in Queensland, NSW and South Australia.
CSIRO Entomology researcher, Dr Paul De Barro says while the pest has not caused severe problems to crops in Australia yet, its potential for damage is enormous.
"In 1991 it caused an estimated $750 million worth of damage to crops in California," he says. "Our research aims to ensure this does not happen in Australia."
The silverleaf whitefly damages crops by sucking out the nutrients from plants leading to smaller, poorer quality produce. It also covers plants in a honey-like dew leading to the growth of a sticky, black mould that is hard to remove from fruit and vegetables.
The silverleaf whitefly also carries several plant viruses that can add to the devastation of crops.
"Many of these viruses are not known in Australia but as the whitefly moves further north, there's a great risk that it will link southern growing areas with northern Australia and southeast Asia where these viruses are known to occur," Dr De Barro says.
"Overseas research shows the whiteflies build resistance to pesticides very quickly. This meant we needed to find some natural enemies of whiteflies to provide growers with a non-insecticide tool."
Early research revealed the presence of two closely related native whiteflies in Australia - one of which lives on saltbush.
"Our theory is that this pest originated in Australia millions of years ago when it was part of Gondwanaland," Dr De Barro says. "This may explain why we have found 12 different species of small wasp in Australia that can attack the silverleaf whitefly.
"Two of these tiny Australian wasps are as good as any other natural enemies in the world at destroying the silverleaf whiteflies."
One of the benefits of using Australian wasps instead of introduced kinds is that they can reproduce without male wasps - the females produce more females. This means that populations of the wasps build up quickly and curb silverleaf whitefly populations.
The two tiny Australian wasps are new to science and were discovered at Warra in the Darling Downs and Townsville in north Queensland.
The wasps' larval grubs attacks whitefly nymphs by boring a hole in them and eating them as they develop into adult wasps. This kills the whitefly nymphs. CSIRO research has proved the worth of the tiny wasps in glasshouse trials.
Field trials at Ayr in Queensland are seeking to determine how many wasps are needed to control different numbers of silverleaf whiteflies on one plant. They are also looking at the effect of climate on both pests and predators.
The results to-date are very promising and future trials are planned for early next year.
"In the future we should be able to recommend to growers the best way to use these wasps with insecticides to control the silverleaf whitefly pest," Dr De Barro says.
"This will save growers money and decrease the likelihood of the pests developing resistance to insecticides.
"These wasps are our insurance against the silverleaf whitefly becoming a bigger problem in the future in Australia," Dr De Barro says.
More information:
Dr Paul De Barro, CSIRO 02 6245 4344 (work), 017 182 316 (mobile)
Louise Lawrence, CSIRO 02 6246 4087 (work)
Jenni Metcalfe 07 3846 7111 (work), 040 8551 866
(mobile)
Broadcast quality footage is available of the silverleaf whitefly
experiments - including close up shots of wasps, whitefly on
crops and crop damage.
Photos are available of the trial, the silverleaf whitefly, and
the tiny wasps.
(Australia's largest scientific research organisation)
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