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24Oct

NZ scientists help Italians deal to destructive bug

Even a rural Cantabrian used to working in the shadow of the Southern Alps would not fail to be awed by the soaring mountain peaks around the northern Italian town of Trento. Despite sitting at a relatively low 190m above sea level the town is dominated by glacial peaks rising almost vertically to 1,000m, often with highly productive orchards sitting two thirds of the way up their flanks.

But this idyllic scene also belies a battle being waged between scientists and the Brown Marmorated Stink Bug (BMSB). The voracious pest first established in the Trentino region two years ago and is now dangerously close to wiping out many crops in one of the country’s most productive horticultural regions.

The pest’s incursion was originally from Switzerland to the north, and was first documented by Italian researcher Professor Claudio Ioriatti in 2016. This year he has already trapped 10 times the number of bugs than he did last year. Professor Ioriatti is based at the nearby Fondazione Edmund Mach research centre which has rapidly become a war room and brains trust for dealing with the Asian based bug that has no known predators in Italy. Professor Ioriatti is backed up by a team of PhD candidates and scientists regarded as the best in the world at understanding pests, and developing new techniques for dealing with them.

This includes Professor Max Suckling, New Zealand’s foremost authority on pests and pest control. Much of his working life has been spent at Plant & Food Research at Lincoln, and since 2014 he has been professor at Auckland University School of Biological Sciences. Professor Suckling has spent the Kiwi winter seconded in the Trento sunshine to work alongside the Italian scientists.

Between these two men and their team of smart researchers there is hope the onward march of the BMSB may yet be slowed, if not stopped, but there is much work to be done. “The first reports of crop damage came quickly in 2017 and now growers are having to spray heavily to try and slow the bug’s advance,” says Professor Ioriatti. 

Estimates to date are that the bug is inflicting Eu150 million a year of damage to crops, and it has nearly wiped out Italy’s Eu300 million pear growing sector.

It is its voracious indiscriminate appetite, and ability to travel long distances on foot, while also being relatively resistant to most sprays that have Italy’s horticultural sector on high alert. “Already after this short period of establishment peaches are badly affected in nearby Emilia Romagna, and high value organic apple crops will suffer – the bug simply laughs at organic pyrethrum controls,” says Professor Suckling. The region provides a wide and varied diet for a bug that overwinters in houses and buildings before emerging over spring time to hatch several batches of eggs a week over their four month lifespan.

The damage they inflict upon the fruit is similar to codling moth. Injecting an enzyme into the fruit causes damage, causing it to fall early and either making it unmarketable or drastically affecting shelf life.He is acutely aware of New Zealand’s vulnerability should the bug be detected here. So far only isolated numbers have been found, often in shipping containers and imported vehicles.

Late last year a vehicle carrier ship that had live stink bugs on board was ordered to leave New Zealand waters after their detection by biosecurity. Port areas including those hosting large cruise ship arrivals are particularly vulnerable, and industry bodies including Biosecurity NZ have done much to raise awareness of the risk the bug poses to almost all of New Zealand’s vegetable and fruit crops.

After the fruit fly it is New Zealand’s next most unwanted pest.

A collection box holding trapped bugs highlights why this is so. Within the box held in the Trento field lab, assorted vegetables and fruits are crawling with the bug, happily and indifferently devouring whatever is put in front of it. Max Suckling admits he has a grudging respect for a bug that can establish itself so quickly and dominate such a variety of crops. He emphasises that here in New Zealand the bug’s threat is not only to the $5.5 billion horticultural export sector.

“It is happy to feed on ‘bridging’ food like native plants and grass seeds available before some crops ripen and it is drawn to maize as soon as cobs start to tassel.”

This highlights how vulnerable areas with mixed cropping, horticulture and pastoral activity, indeed much of New Zealand, are to its incursion. The fact its habitat spans houses, orchards and even the steep forested hills around Trento has Professor Suckling calling for an area wide control programme, similar to what he successfully oversaw during the painted apple moth outbreak in NZ in 1999.

Professor Ioriatti also regularly visits New Zealand, and his last trip in June he spoke to New Zealand orchardists around the country, highlighting the impact the bug has had. He had their full attention, with one grower who had been orcharding for 50 years saying it was the most frightening bug he had heard of. Professor Ioriatti says working with the New Zealanders, including Professor Suckling, has boosted the intellectual horsepower between the two hemispheres, and also provided two summers a year to work on understanding the bug in Italy, and continuing on control/trapping research in New Zealand.

“I do fear though it will be a matter of when, rather than if the bug arrives in New Zealand,” he says.

Professor Suckling suspects any arrival is most likely to come via Australia where 10 incursions have already been detected. It has also established near Santiago in Chile. Professor Ioriatti admires the collective government-industry efforts in New Zealand to deal with incursion risk, and says the best thing this country can do is buy as much time as possible with vigilant controls giving researchers more time to grapple with ways to eliminate the bug. New Zealand has approved the use of a biological control should the bug ever be found in numbers here. The Samurai Wasp has Environmental Protection Authority approval for release, should it be needed.

However Italian law prevents non-native species being used in biological control, something that is hopefully due to be changed through the Italian parliament this year. Scientists are trialling a number of trapping methods as options to spray control which has had limited success on its own, and one where over use threatens to impact of low residue premiums on crops. One method is a sterile male release programme, similar to what Professor Suckling developed for codling moth control in Hawke’s Bay. Dropping large numbers of sterilised male moths by drones across wide orchard areas resulted in a 10 fold decline in moth numbers. It has also enabled growers to minimise the amount of spray required, keeping low residue premiums on their apples. Pheromone traps are also being trialled, along with a relatively new and unknown science of biotremology.

This “Pied Piper” technology utilises vibrations that mimic insects’ mating calls to draw populations of one sex into a trap, and Trento is at the cutting edge of this rapidly developing technique. Both Professor Suckling and Ioriatti are optimistic they can at least curb the bug’s advance, but caution that the bug is moving quickly and keeping up with it with adequate funding for trial work and research is absolutely critical. “The bugs are moving faster than we are at this stage,” says Professor Ioriatti.

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