A vicious micro-wasp from Papua New Guinea has emerged as a knight in shining armour set to rescue Queensland's multi-million dollar fruit industry.

CSIRO scientists at Brisbane's bug-busting laboratories have found the pin-head-sized insect preys on a moth causing millions of dollars worth of damage every year.

It lays its eggs inside the eggs of the fruit-piercing moth, providing a ray of hope for fruit farmers across the State. A major trial of the micro-wasp's potential to control the pest has now started in Western Samoa, where authorities are desperate.

The country's important citrus industry is on its knees, meaning a vast loss of currency to the impoverished nation. If the trial is successful, the wasp will be introduced into Queensland.

The moth, Latin name Eudocima salaminia, attacks tomatoes, peaches, oranges, guavas, pawpaws and even persimmons and lychees. And despite its beautiful velvet-like appearance and golden yellow underwings, it is a farmer's nightmare.

It only likes ripe fruit, and the tip of its half-inch-long proboscis - or feeding tube - is armed with a razor-sharp drill which can penetrate even the tough exterior of a lychee. Once pierced, the fruit is ruined, while the fungi introduced in the process rapidly spoils all neighbouring fruit.

"With Lychees now worth $80 a crate, it is a cost farmers cannot afford", said Dr. Don Sands, 52, the award-winning CSIRO scientist at the helm of the project. The moth's breeding cycle occurs deep in the forest, which explains the cage full of moths set up in a mini-rainforest in a spare patch of ground at the Indooroopilly research station.

Dr. Sands, who won a UNESCO science prize for introducing an unknown South American weevil to control the weeds clogging Australian lakes in 1980, is a great fan of micro-wasps in general.

"They are very specific about what they prey upon, which in terms of biological control is ideal," he said. "That means that when the numbers of their hosts have declined, they too will decline. They won't switch to something else".

Dr. Sands is well aware of the public suspicion surrounding biological controls following the disastrous example of the cane toad.

It was introduced from Hawaii in 1935 to eat grey-back beetles destroying cane crops, but became a major pest in itself as it proceeded to thrive on every other insect in Queensland.

According to Dr. Sands, though, today's scientists would never have introduced an animal with such a wide diet.

Before the micro-wasps are let loose in Australia, the four-person research team will ensure they don't prey on other species of moth which cause no damage, for example.

"So far though it looks good," said Dr. Sands. "Micro-wasps are shaping up to provide an answer to many of our pest problems. They usually have a very small dietary range. If you can find the right one to eat the host, you can solve a lot of problems."

The project has been running for three years and costs taxpayers several hundred thousand dollars a year. But the potential rewards in a solution to the moth plague are enormous.

Fruit-growing, especially for the lucrative Asian market, could be one of Queensland's most important export industries in the 1990s.

The moth destroys a big share of the crop - sometimes as high as 80% and every three to five years a massive outbreak causes monumental damage.

Dr. Sands stressed that the biological control method wasn't the only line of attack. Another approach focuses on baited moth traps farmers can leave out in the fields.

Pesticide sprays are ruled out though. Because the moth only attacks ripe fruit, indiscriminate spraying would result in contaminated harvests.

"We're not talking about eradicating them," Dr. Sands said. "The National Parks people wouldn't be very happy with us if that was our approach. But we're talking about bringing numbers down through a parasite that attacks nothing else but that particular host."

A childhood fascination with creepy-crawlies sparked Dr. Sands' life-long interest in bugs. He has already used another variety of micro-wasp to great effect, helping control the white-wax scale attacking citrus fruit in the 1970s. "It was a dreadful pest," he said. "The only way of controlling it was to spray the fruit with a petroleum compound, which became very expensive for farmers with the rise in oil prices in the 1970s. "We brought in a little parasite wasp and it was so effective that you hardly find either of them now. The wasp and the scale have balanced themselves out."

Guy Ker,
Article from Sunshine Coast Subtropical Fruits Assoc.(Inc.) Newsletter Feb. '90

DATE: January 1992

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