NZ Farmer - Sterile codling moths offer fruitless sex to help wipe out the pest

Written by Heather Chalmers

Thousands of sterile codling moths are being dropped by drone onto central Hawke's Bay apple orchards to help wipe out the destructive wild population of the pest.

Mr Apple technical manager Robbie McCormick said if codling moths were eliminated from Hawke's Bay it would open new high-value export markets.   

India, Japan, China, Taiwan and Western Australia do not accept apples from regions affected by the moths. 

The organic technique also reduced insecticide use. Based at Whakatu, near Hastings, Mr Apple exports about 25 per cent of the New Zealand apple crop. 

Plant and Food Research scientist Jim Walker said that in a single 10 minute flight, a drone following GPS co-ordinates and fitted with special moth-carrying pods can distribute 23,000 moths over a 100 hectare orchard.

"It's a very efficient and effective way of getting moths spread uniformly across an orchard, Walker said.

The wild moth population had been reduced by up to 98 per cent across the 400ha of central Hawke's Bay orchard treated with sterile moths, he said.

"Of 80 pheromone traps, we caught one wild codling moth between them in a season."

The sterile moths, imported from Canada, have the same drive to mate, but no progeny result. By flooding the wild population with up to 60 sterile moths for every fertile moth in the treated orchards the wild populations collapse.

Sterile moths are introduced weekly during the growing season.  

"Within two seasons we expect the codling moth population will be eliminated from these orchards," Walker said. 

To help identify the two moth types, the sterile moths were fed food colouring to make them red, while the wild fertile moths were white, he said.

The same technique was used by the citrus industry in South Africa, where 23,000ha of orchards were treated to control false codling moth. 

The same method could potentially be used to eradicate other insect pests, such as a Queensland fruit fly incursion. 

Codling moth (Cydia pomonella) were found in all apple-growing areas of the world and considered to be one of the most destructive pests of apples because its caterpillar feeds inside the fruit.

Signs are an infected core and access hole ringed with brown frass (residue from chewing or excrement). Damage lowers the market value of the fruit and makes it unfit for human consumption.  

New Zealand Apples and Pears technical manager Tim Herman said the industry was always looking for new and innovative ways to control codling moth to reduce the use of insecticides. 

"We already produce fruit with very low residues, but this research will add to our already sustainable programme of codling moth control and help maintain our ranking as the most competitive apple and pear industry in the world."