City-dwelling insect pests can be a barrier to grower and official efforts to eradicate them, as fruit fly incursions in Auckland have made plain.
A recent research project has highlighted how significant urban insects can be when it comes to eliminating them and how householders are more than happy to help kill them with non-spray methods.
Plant and Food researchers have taken their work using the sterile insect technique (SIT) on codling moth in Central Hawke’s Bay a step further as they try to better understand how the moth’s city cousins can affect numbers and infestation levels.
The moth has long been a problematic pest for apple growers who face ever-increasing pressure to reduce spray levels but also control its impact on crops.
SIT work was done on seven remote orchards totalling 400ha at Onga Onga, near Waipukurau.
In a world-first the researchers pioneered using drones to drop sterile male and female moths onto orchards, effectively forcing out wild populations by sheer numbers and breaking the generational cycle of moth populations.
An average 50ha orchard will be doused with 10,000 sterile moths in a single flight taking less than 10 minutes. One pass a week is made over the orchards between November and February.
“It has proved to be not only a world first but also highly successful,” researcher Rachael Horner says.
“There has been up to a 98% drop in moth populations in orchards and the damage is simply not seen now.
“It has also been achieved using almost no insecticides, meaning ultra-low residues and no larvae in fruit so orchardists are able to access higher-value markets as a result.”
With New Zealand’s relatively relaxed drone regulations and development of 3D printed equipment to contain the moths the researchers believe there are big opportunities for further sterile dispersals in other crops and areas.
But researchers are also concerned there has been no attempt in NZ to try to identify potential sources of urban moth populations that could provide a reservoir population to re-infest orchards.
“So we put 200 pheromone traps across Hastings city and mapped host trees around the pilot eradication orchards at Onga Onga. The traps in Hastings caught 1000 moths, which is a significant number, and only 16% of the traps caught no moths.
“The Hastings traps in host trees caught significantly more males than traps in non-host trees, with some clustering of populations. The traps in the orchards with the most stringent moth management programmes averaged half the catch rate of the Hastings urban traps,” she said.
Orchards with less rigorous moth controls had a fivefold higher catch rate than orchards with strict controls.
Hastings is a particularly relevant city given most of the urban area is a kilometre or less from an orchard. The codling moths are quite capable of covering 1km between trees, Horner said.
“We know that in Canada this urban reserve of pests has proved a real issue in trying to control them.”
Knowing the intensity of the moths’ presence in urban areas gives the researchers confidence to expand any future control measures beyond orchard containment.
“It was apparent few urban households were that focused on a programme to control codling moth in their backyard trees.”
The researchers’ confidence to consider future control programmes is also buoyed by good support from urban householders who were happy to have the traps on their properties.
Science group leader Professor Max Suckling said people are very aware of the biosecurity element of the work.
“By working with the community on existing pests of local industries, like codling moths in apples, we hope to help engagement in biosecurity overall,” he said.
Having the urban data means ultimately the SIT technique might be applied in urban areas but the next step will be to use the technique on the wider Central Hawke’s Bay apple growing area.
“We have strong support from industry keen for us to expand it because they understand it opens up those high-value markets for them,” Horner says.
The Queensland fruit fly is another pest in researchers’ sights for SIT application using drones. Overseas growers are interested in the work done here but till now have used only fixed-wing aircraft.
“The drones enable us to get closer to the trees, they are cheap to operate and are less obtrusive.”
Longer term, researchers hope irradiation techniques will enable pest bugs like the feared brown marmorated stink bug to also be controlled using SIT, something Italian and NZ researchers are working on.
