Solar power against pest

Harvey Gadd with one of his solar light guava moth traps.

The fruit driller caterpillar or guava moth Coscinoptycha improbana was first observed in New Zealand in 1997 on citrus fruit at Ahipara.

The moth, which originates in Australia where it is not considered a pest, was found at Kerikeri in 2000, Whangarei in 2006, Auckland in 2008 and is now in Waikato.

The insect is steadily spreading south - habitat requirements suggest it could reach Christchurch - munching its way through feijoas, guavas, loquats, plums, peaches, citrus, pears, apples, macadamias and other nuts along the way.

In New Zealand the moth seems to have no natural predators so it poses a huge threat to Northland commercial growers of fruit it targets.

But on the home front, Harvey and Elizabeth Gadd are fighting back with cheap technology which seems to be clearing the invader from fruit trees in their Whangarei Heads neighbourhood.

Carolyn Nicholas, of Paihia, pointed the Reotahi couple in the right direction with a letter published in a gardening magazine four months ago explaining how solar-powered garden lights could be turned into moth traps.

Retired teacher Mr Gadd, 73, bought 10 small solar lights from Mitre 10 for $2 each, sealed small moisture control holes in their bases with epoxy putty and heated a 25mm metal pipe with a blowtorch so it could cut holes in the plastic sides of the lights. The holes allow moths to be lured inside lights, where they make contact with a little cooking oil poured into the base, get stuck and die.

"We put nine lights in our orchard and on the first night we used them we got five moths," Mr Gadd said. "Considering each female moth could produce about 200 eggs it wasn't a bad start."

The couple told their neighbours about their success and got another 20 lights to defend their fruit trees.

"All the macadamia nuts, peaches, plums and feijoas around here were devastated by guava moth last year. But this year, with moth numbers knocked right back, everyone is getting good fruit off their trees."

Meanwhile, Trapz NZ Ltd director Bob Mitchell, of Kerikeri, produces a "Little Bugga" trap which uses a battery-powered ultra-violet light diode to control guava and codling moths and retails at $75.

-No insecticides are registered for use against guava moth, according to the Northland Regional Council website. Commercial orchards disrupt guava moth mating with Asian peach moth pheromone dispensers and wrapping green fruit with fine mesh cloth prevents guava moths from laying eggs on ripening fruit.