health & science
Preparing for the war on stink bugs
Spring marks the beginning of brown marmorated stink bug season, Farah Hancock reports on the dogs, wasps, lures and sprays ready to take on a costly invader.
Georgie has a particularly unpleasant but important job. She’s trained to sniff out brown marmorated stink bugs, which are said to smell a bit like sweaty socks.
She’s just one of New Zealand’s tools in an incursion toolbox which includes sniffer dogs, traps, lures, heat treatment, sprays, samurai wasps – and a motivated public ready to catch and photograph suspicious bugs.
If stink bugs became established in New Zealand the impact would be devastating to the tune of billions.
Red wine could taste like fetid socks, orchard fruit sucked by the bugs becomes puckered and “cat-faced” and only good for juice. In Italy the stink bugs are so destructive entire orchards are sealed in giant netting bags to save produce.
It would take as few as 10 bugs and two years of rampant breeding for a problem to unfold in New Zealand. Each female bug can lay approximately seven to 10 batches of 20 to 30 eggs.
Last year four contaminated ships were turned away from New Zealand and 151 live stink bugs were intercepted at the border. September 1 marks the beginning of stink bug season, when they’re most likely to arrive tucked away in imported vehicles and machinery.
New rules require importers treat cargo offshore. The rules, which came into effect in July, apply to vehicles, machinery and parts from 33 countries identified as a risk and all sea containers from Italy.
What happens if some bugs do get in though? Ministry for Primary Industries Dr Catherine Duthie has been plotting for eight years how to tackle a stink bug incursion and is busy building an attack toolbox.
“Eight years ago, I was certain that we would have found a population by now … we’ve held off the problem. I’m not sure we can continue to hold it off looking at the spread through Europe.”
Finding stink bugs
The first step to fighting an incursion is finding bugs. Georgie works at Auckland Airport and port sniffing out bugs and has found plenty in imported cars.
She’s one of three detector dogs trained in the art of stink bug detection. However, the training posed a problem, said Duthie. Importing live bugs for training would be a risk, so how do you train a dog to sniff out something which doesn’t yet exist in a country?
A project with the United States Department of Agriculture was undertaken to see if dogs trained with dead bugs would then be able to sniff out live bugs. Dead bugs turned out to smell very similar to live stink bugs.
“We are able to bring in dead bugs without any risks or any problem into the country and train our dogs using those bugs.”
The dogs are mainly based at airports or used when an incursion is suspected. In Tauranga where a single stink bug was found, dogs helped in the search for more. None were found.
Lures and traps are another way to find the bugs. Duthie describe pheromone traps as a “nifty little device”. They’re being trialled as an early warning system close to ports. Unlike the fruit fly traps which attract only male flies, the stink bug traps lure male, females and young.
“It’s got a pheromone. It mimics the pheromone the male stink bug emits when he’s actively feeding. What that signals to the rest of the population is ‘Hey, there’s good food over here, come and join me’.”
What’s the most likely scenario?
Overseas experience show homeowners are likely to be the first to spot bugs as they move inside in autumn to find a warm spot for winter.
“Somebody might see a couple of bugs in their house and goes ‘Oh, that’s a bit weird’ and call that in.”
With the bugs hibernating over winter hidden in dark, warm spots, waiting until hunger and spring warmth gets them out of hiding places could be the easiest way to target them.
“We know what host trees they’re attracted to. We know we can draw them into those trees using lures … we would douse those trees with insecticides.”
It won’t be anything like the Asian gyspy moth response which saw planes buzzing over West Auckland aerial spraying.
“These insecticides are general insecticides and they’ll kill everything. We want to use them in a targeted manner.”
Releasing the samurai wasps
A natural predator of the stink bug is the samurai wasp. The import and release of wasps has been pre-approved and would be a mop-up measure after spraying.
The pinhead sized wasp lays larvae inside the stink bugs’ eggs. The wasps’ larvae use the egg as a tasty incubator, eventually chewing their way out and destroying the egg in the process.
“We use the term ‘inundative’ release, which means we want to over-flood the populations, so every egg has the potential to be targeted by a parasitoid wasp,” Duthie said.
For a small-scale stink bug incursion Duthie estimates that would mean about 100,000 wasps.
There’s a hitch in the plan though. How do you rustle up an army of samurai wasps in a hurry? Rules say you can only release the second generation of wasps, not fresh imports, to reduce biosecurity risk, but to grow the next generation in a contained facility you need their food source – stink bugs. Similar to training Georgie the stink bug dog, using live bugs is a risk.
Duthie said the solution is being investigated. Crediting an offshore facility so imported wasps can be released immediately is one option. Another is to import stinkbug eggs, fertilised and possibly frozen.
What’s the chance of eradicating stink bugs?
No country has managed to eradicate stink bugs once they’ve become established.
Georgia in eastern Europe has also been trying hard to get rid of them as the bugs have impacted their hazelnuts, stone fruit and wine industries.
“The impressive thing that the Georgians have done is it's a coordinated effort of control in every other country that has stink bug problems, it's really just the growers who are applying control methods in their own crops.”
Growers are spraying crops at the same time, and there’s also spraying of surrounding vegetation.
“They are using an extraordinary amount of chemicals. They are having a big impact on the [stink bug] population.”
Duthie hopes continued efforts will keep stink bugs out of New Zealand for a bit longer.
“I really hope that we have some more selective chemicals by the time we have to mount a response. That would be nice. That's one of my worries, the fact that we have to use these broad scale insecticides.”
Duthie said the public can help by catching bugs which look like stink bugs and contacting MPI.