Our Changing World: Building an army to stop a stink bug invasion

Source: Radio New Zealand

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In February of this year an adult male brown marmorated stink bug (BMSB) was found in a trap in Ōrākei, just along the coast from Auckland’s port.

“They can come on imports in containers or in used vehicles and machinery,” says Dr Scott Sinclair, manager of the Biosecurity New Zealand operational readiness team which handles threats to our plants and the environment at the Ministry of Primary Industries (MPI).

“And they can obviously then come on the passenger pathway, so via people’s luggage and other paraphernalia like that.”

Scott told Our Changing World that the recently caught BMSB was found in a new type of trap and the response was swift, with more traps placed in the surrounding areas. Thankfully, no further bugs were detected.

So, “It’s really just considered to be an outlier,” he says.

What an invasion might look like

That is a good thing, because we definitely do not want BMSB to set up shop here in Aotearoa.

“It feeds on over 300 host plants. So whatever you can imagine, it will feed on,” says Dr Gonzalo Avila who took RNZ’s Our Changing World on a tour of his lab at the Bioeconomy Science Institute (BSI) where work to build an army to protect New Zealand against a BMSB invasion is taking place.

“Of course, [BMSB] has its preferences, but it would do very well in apples. It would do very well in cherries. It would do very well in kiwi fruit. In the United States, it caused massive destruction to the apple industry there.”

New Zealand’s native flora is also unlikely to escape unscathed.

“All our native plants are in specific families, and BMSB is known to attack plants in the same families. So, they would be potentially at risk as well,” says Gonzalo.

And then there’s the smell. If you have ever come across a native shield or stink bug, you will know the scent they give off when threatened. Karina Santos, Senior Research Associate at the BSI, says BMSB is on “another level.”

“The power is stronger and when they are in big numbers… the chemical that they release can intoxicate humans.”

The high-risk season for BMSB runs from September until April, as the Northern hemisphere-based bugs find places to overwinter, including inside shipping containers and other things being exported.

There is a real concern that it’s not a case of if BMSB will come in, but when.

The solution?

Just behind the towering industrial BSI building in the heart of Auckland’s Mt Albert, is the squat concrete building which Gonzalo fondly nicknames Area 51.

“Because we’re rearing aliens. We’re bringing insects that are not present in New Zealand and they need to come into containment.” These ‘aliens’ are the potential weapon against BMSB – the samurai wasp.

At first glance the wasp doesn’t look like much. It’s tiny – about the size of an ant. But sticking with the Alien theme, the samurai wasp has some similarities to the chestburster in the Sigourney Weaver movies. It’s a parasitoid, mainly eating nectar from flowers, but needing a host to reproduce. So, the teeny wasp lays its eggs inside a BMSB egg – the larvae kills its host – and instead of getting a stink bug hatching you get a wasp.

While it might not live up to its name in looks – the samurai wasp or Trissolcus japonicus is the natural enemy of BMSB.

Neither of these insects, which are native to East Asia, are in New Zealand yet but in 2018 the Environmental Protection Agency approved the use of the samurai wasp if BSMB ever became established.

The idea is if you get a pest insect into the country, you recruit its home predator to help you. We’ve done this before – dating right back to the late 1800s when ladybirds were brought in to deal with aphids.

A lot of the work being done by Gonzalo and Karina is to make sure we understand just what releasing this biological control might mean and what it would entail.

Building the army

Ensuring we can quickly create an army of samurai wasps to handle a BMSB invasion is one of the problems Karina has been looking into.

She’s experimenting to see if the samurai wasp could be reared using the pittosporum shield bug, which is an exotic species that showed up here in New Zealand in the 1950s, and they have another project, funded by MBIE, which is looking into developing artificial stink bug eggs.

“We are now at the phase that we are developing our first prototypes of artificial eggs,” says Gonzalo.

And to attract the wasps, Karina is testing out stink bug perfume on steel balls, which look a lot like the ones you might use to decorate a Christmas cake.

Gonzalo explains that the steel balls are covered with volatiles from the brown marmorated stink bug and if they figure out an attractive perfume, they’ll then hone in on which are the specific chemicals that are enticing the wasp.

An army on ice

Mass rearing isn’t the only option for building the army. Another recent study looked at bringing in the wasps and keeping them on ice.

The team managed to import around 12,000 parasitoid wasps and more than 90 percent of the females survived.

“We wanted to try to see for how long we could keep them alive and still be viable,” says Karina, “Because one thing is that they survive, but the other thing is that they survive, but they also attack and reproduce.”

The results were positive.

“Yes, they can do that.”

Unleashing the army

The decision-making about when and how to release the samurai wasp, would fall to MPI’s Biosecurity New Zealand, and Dr Scott Sinclair says “It’s a really cool idea, but it’s something that’s really difficult for us to operationalise and particularly to operationalise rapidly because there’s some really challenging logistical constraints.”

This is because we would need a huge population to make a dent in a BMSB incursion.

“So, it’s unlikely that we’d be using samurai wasps, I would say, within the first year of a response,” he says, “But as things move forward and we can think about some of those logistics and how it’s challenging to put those out into the environment, then that process would probably happen, in subsequent years.”

Figuring out the best way to grow this army and then deploy it is not an easy thing, says Gonzalo.

But Gonzalo stresses just how important it is to keep working on ways to combat BMSB, because the threat to New Zealand is so high

“We don’t want to play the Russian roulette here and see what happens. The consequences of doing nothing would be so high.”

If think you have found a brown marmorated stink bug, don’t kill it. Catch it. Take a photo and contact Biosecurity New Zealand.

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– Published by EveningReport.nz and AsiaPacificReport.nz, see: MIL OSI in partnership with Radio New Zealand