Border officials have been intercepting higher numbers of a feared pest insect that could prove devastating if it became established here – but it's unclear exactly why.

Several car shipments have been turned away after it was discovered they were infested with the brown marmorated stink bug.

The hard-to-see, hard-to-kill, fast-breeding scourge has managed to spread around the world from East Asia and is one of New Zealand's "least wanted" pests.

Their arrival here would be a nightmare for our agricultural sectors, native plants and us – the bugs could invade our homes and sheds, especially over winter.

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"Some people may show allergic reactions to stink bug secretions, excrements, and other remains," said Dr Michael Rostas, of Lincoln University's Bio-Protection Research Centre.

Late last month, officials ordered the Glovis Caravel to leave New Zealand after crew found nearly 600 stink bugs - 12 of them alive – while the ship was docked in Auckland.

It was the fourth in a recent spate of stink bug scares, which have prompted the Ministry for Primary Industries (MPI) to boost its border inspection and verification of bulk carriers arriving from Japan.

"Increased interceptions may also be the result of greater inspections in New Zealand as the risk has become more apparent," said David Teulon, director of joint agency Better Border Biosecurity (B3).

"The reason for the recent increases in interceptions from Japan is not fully understood."

Dr Glenn Aguilar, a senior lecturer and environmental scientist at Unitec, said most of the detections occurred at ports, and mostly in imported cars.

"Hence in terms of invasion, the greatest risk would be Auckland with the highest amount of imported cargo," he said.

"This would be followed by other areas with the risk proportional to the amount of cargo being imported."

Asia was now considering mandatory pre-export treatments using methyl bromide, sulfuryl fluoride or heat, as the US and Italy had recently ordered on all vehicles, machinery and other cargo leaving their shores.

Vehicle Importers Association (VIA) chief executive David Vinsen said disruption to the industry had been severe, as at this time of year about 12,000 vehicles were imported a month.

Vinsen said "there is a huge backlog building up" and customers would already be noticing the "dearth of stock".

"That demand is not being satisfied."

With thousands of jobs on the line, employers were desperate to hold off on losing any staff because they knew the work would start flooding back in when the cars were cleared.

Vehicle Importers Association (VIA) chief executive David Vinsen said the disruption to his industry had been severe. Photo / File
Vehicle Importers Association (VIA) chief executive David Vinsen said the disruption to his industry had been severe. Photo / File

But Vinsen said MPI was doing the right thing, and the industry was happy with how the threat was being met.

"We don't want to be doing anything that could threaten our biosecurity in New Zealand."

The threat

The stink bug had more than 100 host plants and was a pest of many vegetables, fruits and field crops. Most at risk in New Zealand was kiwifruit, apple, apricots, pears, vegetables, wine, other fruit and plant seeds.

"The kiwifruit industry estimates fruit loss could be up to 30 per cent," Rostas said.

"In a worst-case scenario, outbreaks could also be expected in macadamia and several vegetable crops such as tomatoes, capsicum and sweetcorn."

Rostas said the bug could quickly establish in large parts of New Zealand, mainly in the North Island and the northern part of the South Island.

In the US, it took the bug just 14 years to become one of its most significant pests in recent history.

Here, New Zealand growers would be forced to drastically increase the use of broad-spectrum insecticides to prevent significant damage; American orchards had suffered four-fold losses.

Rostas said that could lead to higher residue levels in fruit and vegetables and would have detrimental effects on beneficial insects – such as predators, parasitic wasps and pollinators - leading to the outbreak of secondary pests, like mites, aphids and scales.

"Most importantly, it would be a huge setback for sustainable pest management programmes and a serious threat for organic growers," he said.

"The wine industry could be affected because only a few bugs feeding in grape clusters during harvest may taint grape juice and affect wine quality."

If the bug became established here but not in Australia, we could also expect trade restrictions.

There were also fears for taonga plant species: the bug's preference for berries may put plants such as karaka or kowhai at risk.

Flowers and seed heads of many species used for traditional Maori medicine, like harakeke, would be attacked, as would important plant species like karamu.

Harakeke and karamu were also important food sources for native birds.

Aguilar said we could expect the threat to grow under climate change.

A model for current climate conditions showed most of the country was already highly suitable for the bug, and when future warming was added to the simulation, the range could move further south.

"Large areas of the South Island, as well as the southern areas of the North Island, become more suitable for invasion and, as such, increases the likelihood of establishment in New Zealand and impact to crop production."

What can be done?

Many projects are under way to help prevent an incursion, or develop agents to respond to one.

Teulon said a surrogate stinkbug was being used to provide MPI with a full dataset on fumigants – such as methyl bromide and sulfuryl fluoride – along with heat and the more environmentally friendly ethyl formate.

New Zealand's kiwifruit industry could face losses of up to 30 per cent. Photo / File
New Zealand's kiwifruit industry could face losses of up to 30 per cent. Photo / File

Several studies were examining whether biological characteristics, such as odour or sound, could be used to detect them on their way to New Zealand or at the border.

Considerable research on trap and lure development had been done in the US primarily for pest management purposes.

Further MPI-commissioned work was developing fit-for-purpose trap and lure combinations for border use in New Zealand.

"The suitability of these traps for surveillance use was successfully trialled in Chile recently and the traps are being considered for New Zealand's response plan," Teulon said.

But the potential for biocontrol agents was limited.

"Extensive research in North America and Europe indicated that local predators and parasitoids are not effective against the bugs and evidence to date would suggest that this will be the same in New Zealand."

The most promising candidate was japonicus, a parasitic wasp not found here.

This was a very small wasp that would only attack members of the Scutelleridae family, which had no species in New Zealand, and the Pentatomidae family, which had eight domestic species.

"Research has been undertaken to determine its risks to non-target species and to understand its potential distribution in New Zealand."

In New Zealand, the release of a classical biocontrol agent is subject to approval by the quasi-judicial Environmental Protection Authority, which implements the Hazardous Substances and New Organisms (HSNO).

In the meantime, MPI was running an awareness campaign urging the public to report any suspicious bugs.