environment

Samurai wasp ready to take on stink bugs

If the brown marmorated stink bug establishes a foothold in New Zealand it will face a tiny but lethal opponent.

The Environmental Protection Agency has pre-approved release of a traditional foe of the stink bug, the pin-head sized samurai wasp.

It is the first time a bio-control measure has been approved in New Zealand before an incursion has taken place.

“We’ve got quite an arsenal lined up. This parasitoid [samurai wasp] is just one of those tools.”

The wasps will be imported if needed, with the most likely source being wasps bred in laboratories in the United States. Samurai wasps do not sting humans.

The wasps lay eggs inside the egg mass of the brown marmorated stink bug. The wasps’ larvae then eat the developing stink bugs before chewing their way out of the eggs. This typically kills 80 to 90 percent of stink bug eggs.

The Ministry for Primary Industry’s Dr Catherine Duthie has investigated measures to eradicate brown marmorated stink bugs since 2010. She said MPI has a range of measures ready to use against the bugs.

“We’ve got quite an arsenal lined up. This parasitoid [samurai wasp] is just one of those tools.”

Other measures include pheromone-laced traps to lure the stink bugs and a spray to kill them. Trained dogs will also be used to help locate areas with bug infestations.

“Essentially the parasitoid is a mop-up measure to make sure that we don’t get any further adult or nymph BMSB into the population.”

The samurai wasp is the size of a pin head. Photo: Supplied

Originally from East Asia, the stink bug has proven to be an adept hitchhiker and has made its way into Europe, the United States and South America. Duthie said it is “reasonably likely” it will reach New Zealand.

“It hides away on things we import. We’ve found it in used cars, we’ve found it on machinery, we’ve found it on people buying Barbie dolls off eBay. Just about anything you can think of, it can come in on,” said Duthie.

In countries with no natural predators, the bugs are voracious eaters and destroy horticultural crops. They also infest homes during winter.

“We’re talking tens of thousands in a house, huge numbers of bugs. There is probably not a single person in New Zealand who is not going to be affected by this.”

It’s estimated if they establish themselves in New Zealand, gross domestic product could fall between $1.6 and $3.6 billion by 2038.

Duthie said stink bugs could thrive in all of the North Island and most of the South Island.

So far, no country has managed to eradicate the stink bugs once they have established themselves.

Duthie said a single bug entering the country on a barbie doll would not pose a threat as alone it couldn’t breed. A group of 10 bugs arriving hidden in a car engine would be a different matter. Each female bug can lay approximately seven to 10 batches of 20 to 30 eggs each.

Undetected and unchecked 10 bugs could pose a serious problem within two years. So far MPI has stopped 2569 stink bugs at the border and no stink bugs have been found anywhere but border checks.

The release of samurai wasps will only take place under strict conditions.

An incursion must have occurred, and the release must be in the same vicinity as the stink bugs. MPI is the only agency allowed to release the samurai wasp.

It must submit a plan to the Environmental Protection Agency before any release can be made. The agency’s organism manager Stephen Cobb said the pre-approval was “ground-breaking”.

“It’s very proactive. If you look at some incursions there have been in the past people have said ‘These things have been anticipated why has nothing been put in place?’.”

A number of bio-control organisms have been approved for release in New Zealand in the past including a wasp to control clover root weevil and another wasp to control coddling moth.

"Bio-control is increasingly what the primary sector and people focused on conservation are looking at as it is considered possibly a bit more environmentally friendly than the use of pesticides or herbicides or chemicals," said Cobb.

Approving a bio-control before a pest was present meant the agency needed to take a slightly different approach than usual, including deciding what criteria would need to be met as part of the conditions for release of the samurai wasps.

"If you are having trouble finding it for host testing, you probably shouldn’t be removing them from the environment because you might do more harm than good.”

Part of the process to gain approval is weighing up risks and benefits of bio-control agents such as samurai wasps. The application for their release received 69 submissions, 65 of which supported the release.

The Department of Conservation did not oppose samurai wasps being approved for release but did express concern samurai wasps may target the endemic black alpine shield bug which is in the same family as the stink bug.

Little is known about the shield bug which is found only in Otago and is classed as ‘at risk’.

Duthie said in laboratories samurai wasps have attacked the eggs of other species of the stink bug family but noted the shield bug’s preferred habitat was vastly different to stink bug and samurai wasps’ habitats.

“We believe that while there is potential there the habitat differences are such that it is very unlikely to be impacted. Even if there aren’t brown marmorated stink bugs around, the wasp is very unlikely to end up in that habitat.”

One suggestion is that an insurance population of the shield bugs be created.

“It’s a very rare species. It’s so rare that we had difficulty collecting it for host testing. There’s always a risk there. If you are having trouble finding it for host testing, you probably shouldn’t be removing them from the environment because you might do more harm than good.”

The approval to release the samurai wasp lasts for 10 years.

MPI advises anyone who believes they have seen a brown marmorated stink bug to catch it and call  0800 80 99 66.

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