health & science

The foul-smelling bugs threatening NZ wine

Hold your pinot noir a little closer tonight. If brown marmorated stink bugs establish themselves, New Zealand’s red wine could taste unpleasant. Italian stink bug expert Professor Claudio Ioriatti visited New Zealand and shared lessons from Italy’s smelly bug invasion with local growers and scientists.

Tasting notes for New Zealand’s red wines could look very different if brown marmorated stink bugs establish themselves here.

New Zealand Winegrowers biosecurity and emergency response manager Ed Massey said stink bugs could cause a loss in production as well as a serious quality issue.

“They’re called stink bugs for a reason.”

When they’re threatened, stink bugs react in a way politely described as “emitting its volatile”. In plainer language, this is a defence mechanism insect fart. A foul-smelling gas is emitted from their abdomen in the hope the stench will repulse predators.

Around grape harvest time stink bugs nestle in the centre of fruit clusters.

“When you harvest your grapes you will also harvest stink bugs, and that is likely to cause it to emit its volatile. It smells a little bit like sweaty gym socks that have been left in the bag for a couple of weeks.”

For white wine the fermentation process destroys the festering gym sock taint. For red wine lovers it’s bad news.

One study investigated how many stink bugs it would take to ruin your glass of wine and concluded 25 stink bugs in 16 kilograms of grapes is enough to make your red wine taste like it's been decanted through a sweaty sock.

Without predators outside of its Asian home turf and with a breeding ability rabbits would envy, hitchhiking stink bugs are a real threat. They’ve infested parts of Europe and the United States.

So far no country has managed to eradicate stink bugs. In France they're called the devil’s thumbtack. In Georgia they're so damaging there’s a bounty of $23 per kilogram of bugs on offer. In Italy they've cost growers thousands.

Massey is also chair of New Zealand's Brown Marmorated Stink Bug Council which consists of industry organisations partnered with the Ministry for Primary Industries. Currently its purpose is to prepare for the risk of stink bugs establishing themselves in the country - a prospect a NZIER report estimated would cost $4.2 billion in lost export revenue over 20 years.

Massey, along with other New Zealand growers and scientists, heard from Italian brown marmorated stink bug expert Professor Claudio Ioriatti, who toured New Zealand during May as part of an Agricultural and Marketing Research and Development Trust conference support programme. 

Massey said Ioriatti’s visit helped inform local producers what management options might be useful if the bugs make it into the country.

“Meeting with people like Claudio and hearing these stories about the tools and technologies that they're researching to improve readiness is critical.”

Professor Claudio Ioriatti toured New Zealand in May sharing his knowledge of the brown marmorated stink bug with scientists and growers. Photo: Supplied

The Italian feast

Ioriatti said stink bugs were first found in Italy in 2012 and found the smorgasbord of fruit and vegetables the country offered “favourable”. By 2016 their effect was devastating.

Stink bugs stick a needle-like mouthpiece into fruit and vegetables and suck out juice. The damage this causes is invisible at first but as the fruit ages a condition called “cat-facing” appears. Fruits dimple, and become misshapen, resembling the puckered cheeks of a cat.

Four years after the bugs were first detected in Italy, Ioriatti said growers estimate bug-related losses to be over $250 million a year. Some growers were unable to sell up to 90 percent of their fruit.

The losses even impacted products you wouldn't normally think of as being at risk from a juice-sucking bug. According to Ioriattia, Ferrero Rocher - reliant on hazel nuts for their gold-wrapped chocolates - lost almost $120 million in 2017. The bugs attacked immature hazelnuts and destroyed them.

“They completely lost production of hazelnut in one year and they have the same problem in Georgia now.”

"Cat-facing" damage on a pear caused by brown marmorated stink bugs. Photo: Getty Images

When asked if Italy has any hope of getting rid of stink bugs, Ioriatti’s answer is swift: “No.”

It’s now a case of learning how to live with them and manage their devastating effects. Management options range from high-tech to low-tech.

Currently the most effective tool is a low-tech option. Essentially orchards are being put in giant bags to keep bugs out.

“Most orchards are already equipped with anti-hail nets. In this case they just need to close the perimeter with an additional net.”

The cage of nets are put in place after insects have pollinated flowers but before fruit ripen enough to attract stink bugs.

Even with nets there's still a need for harsh insecticides as some stink bugs will slip through or may have been in the area before nets went up. However, Ioriatti said nets reduce the amount of spraying by about five times.

The sprays, which affect the stink bugs, are toxic to bees and humans. Without nets, crops need to be sprayed weekly to control the bugs.

Ioriatti said the extra spray needed has made it harder for Italy to meet food export standards for some countries. One technique to reduce overall spray usage by 50 percent has been trialled successfully, where the outside edges of a crop are sprayed first rather than the full crop. Over the following weeks the inner rows are sprayed as the bugs work their way in.

Stink bug eggs are tasty incubators for samurai wasp larvae. Photo: By Oregon State University -  CC BY-SA 2.0

A chemical-free approach is biocontrol, like introducing a predator to control pest numbers. Frustratingly for Ioriatti, biocontrol measures are not an option for Italy, which has a ban on introducing exotic insects. For stink bugs, a predator is the pin-head sized samurai wasp which lay their eggs inside the stink bugs’ eggs. As the wasp larvae grow, they use the stink bugs' eggs for food. This kills 80 to 90 percent of eggs.

New Zealand has pre-approved the release of samurai wasps should a stink bug invasion occur. 

Another method under consideration is breeding the stink bugs, treating them with gamma radiation so they become sterile and the releasing them. Mating between the sterile stink bugs and wild stink bugs result in no offspring and reduce the overall population.

“If you release a sterile brown marmorated stink bug, even sterile it is able to cause damage. So people are quite sceptical about this approach.”

Ioriatti said releasing sterile stink bugs could be effective when small populations are first detected and could be a useful tool in New Zealand if stink bugs are detected.

In Italy, sterile bugs could be released at the end of winter when the wild stink bug population is smaller and there's no fruit which can get damaged. This could reduce the population at the beginning of a season and make management easier.

Ioriatti thinks New Zealand has a good chance of fighting a stink bug invasion. There’s the moat of the South Pacific Ocean and the Tasman Sea, and already strict biosecurity measures in place. Last year ships carrying stink bug-infested cars were turned away and current import rules are due to get stricter. New measures include the heat or chemical treatment of vehicles, machinery and containers from countries with stink bug infestations before they leave foreign ports.

These measures could help buy the time needed to avoid sweaty-sock wine, cat-faced tomatoes and empty hazelnuts. 

“You will be able to delay the infestation and the establishment and during this time you can develop strategies to control them.”

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