New Zealand is on high alert for an invasion of brown marmorated stink bugs (BMSB) – widely regarded as the greatest biosecurity risk we face – after farmers across Europe report record devastation.

Italy has been hit particularly hard during its summer season, with damage to fruit crops including apples, pears, kiwifruit, grapes and stonefruit exceeding €400 million (NZ$675 million), leading to some farmers considering walking off their land for good.

New Zealand scientists have been working alongside Italian colleagues to help develop new methods for monitoring and controlling the bugs.

Like New Zealand, Italy has a wide range of produce, often grown in relatively small, mixed plots. This system works in the stinkbug's favour, as they can easily move from crop to crop.

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"There tends to be mixed cropping systems where you might have kiwifruit in one field and then pears in another," Dr Catherine Duthie, of the Ministry for Primary Industries (MPI) said.

"So that provides a really good opportunity for bugs to move around and feed on their preferred fruit."

The brown marmorated stinkbug originates from Asia, where its numbers are kept in check by predators such as the samurai wasp, which lays its eggs inside the eggs of the stinkbug.

About the same size as an ant, and with none of the annoying habits of the common wasps that dominate our summer, the samurai wasp has approval for release in New Zealand if a stinkbug invasion should occur.

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In her laboratory in Reggio Emillia, in the north of Italy, Dr Lara Maistrello is breeding Italy's native relative of the samurai wasp, to see how well it does in the fight against the brown marmorated stinkbug.

Italy's biosecurity laws allow no path for releasing an imported biological control like the samurai wasp, but desperate farmers are calling for those law to be changed.

A pear ravaged by a brown marmorated stinkbug. Photo / Aotearoa Science Agency
A pear ravaged by a brown marmorated stinkbug. Photo / Aotearoa Science Agency

Maistrello said that the growth in the stinkbug population, first detected in Italy in 2008, has been frighteningly fast – a statement echoed by pear farmer Viller Malavasi.

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"Until 2017 the damage was okay, pretty much," Malavasi said, "but since 2018 the damage is so high we cannot keep up with the cost of production. It's almost impossible to survive, we are seriously thinking about giving it up."

Malavasi's pear crop this year is almost 100 per cent a write-off.

The pears on the trees are gnarled and deformed, the fruit growth stunted by being fed on when they are young.

"They look like monsters" he said.

Adding insult to injury, even though they can't be sold, Malavasi must still pay for the crop to be harvested, as leaving it to rot on the trees will only cause further problems.

In Trentino, further North in Italy, New Zealand Plant & Food Research scientist Dr Max Suckling is working on a range of possible controls against the BMSB, including new traps and other biological controls.

Suckling said the stinkbug is a superpest because of the scale of damage, and points to the fact one bug can become 125 bugs in just a year. The bugs are also very good at spreading across a country.

"It's a hitchhiker, it spreads very, very quickly," Suckling said.

"In a region like this, where you can hear the trains and you can see the cars and the trucks, just moving things around, the bugs are hopping on and hopping off.

"The same thing will happen in New Zealand, it will move through the country quickly. Because it's human-assisted. And if it's a female, and she's able to lay eggs, she'll establish a new population very, very quickly."

This deformed pear illustrates what brown marmorated stinkbugs can do to fruit crops. Photo / Aotearoa Science Agency
This deformed pear illustrates what brown marmorated stinkbugs can do to fruit crops. Photo / Aotearoa Science Agency

With Italy now in winter, the stinkbugs there have gone into over-wintering mode, a state of hibernation where they seek refuge inside houses or commercial buildings by the thousands, causing anguish to homeowners and business operators inundated by the pests.

This is also where the bugs pose the greatest risk of reaching New Zealand – in 2018 a box of shoes purchased from Italy on eBay arrived containing 26 live stinkbugs. Imports from the bugs home countries in Asia are also a threat.

"They might hide out in a used car or a new car that then gets shipped to New Zealand," Duthie said.

"They hide in places like within the door panels and right within the seats, places that we can't visually find them. When they come to New Zealand, the daylight cues, the length of the day tells them, 'Hey, it's summertime. It's time to get out there and feed and reproduce.'"

The Ministry for Primary Industries is urging vigilance, and calling for any possible sightings of the brown marmorated stinkbug to be reported to its hotline on 0800 80 99 66.

- Aotearoa Science Agency