Killers on the wing
We’ve sprayed them, burnt them, put a bounty on their heads and even excommunicated them, but invasive wasps continue to thrive. Fortunately, says the author of a new book on the pests, there’s reason for hope.
We’ve sprayed them, burnt them, put a bounty on their heads and even excommunicated them, but invasive wasps continue to thrive. Fortunately, says the author of a new book on the pests, there’s reason for hope.
If you’ve ever stared into the face of evil, you will know that it’s yellow and black. But if you should dare to get a little closer and peer a little harder, you might just see exactly what sort of evil it is. The German wasp has a little black stripe between its eyes that looks like a nose. Two small black dots just below that look for all the world like nostrils. The common wasp, by contrast, has no dots on its face. Instead the black, nose-like stripe is thicker and looks something like an anchor.
Most of us never take the opportunity to look closely at the face of a wasp. We just feel the sting, or we run like hell at the very thought of one.
Our relationship with the wasp – the common Vespula vulgaris or the German Vespula germanica – is almost universally one of fear and loathing. We humans are about 800,000 times larger than the average wasp and we can splatter one with a rolledup newspaper or blast it into oblivion with insect spray, but when we encounter one, many of us go to pieces.
Phil Lester, a Wellington entomologist who has written an occasionally jolly book about these little yellow-and-black devils, has seen people scream in terror at the sight of a wasp flying by.
“There’s a sort of horror-movie fascination to the wasp for many people – ‘Oh, my god! a wasp!’ – and for many it’s a frightening thing,” Lester says. “They are evil.”
He should know. A professor of biological science at Victoria University, Lester specialises in insect ecology and has studied for decades what biologists called Hymenoptera – broadly, wasps, bees and ants. He has fought the good fight against invasive Argentine ants in New Zealand, yellow crazy ants in the Pacific and, most recently, a parasitic fly threatening Darwin’s finches on the Galápagos Islands. But his greatest foes may be our two most vicious invasive social wasps – the vast majority of wasp species are solitary insects, but V vulgaris and V germanica are highly social species (see box, page 25).
The Vespula were late arrivals here. The Germans invaded in the 1940s and their common relatives became established only in the 1970s. They have been terrifying people ever since. But their fearful reputation isn’t really deserved.
“There’s a sort of horrormovie fascination to the wasp. For many people, it’s a frightening thing.”
Angry nests of wasps are certainly to be feared, and wasps – like bees – very occasionally cause road accidents when they fly through a moving car’s window. Stings, including wasps stings, can cause harm to the small number – around 3% of adults – who suffer the acute allergic reaction called anaphylaxis due to insect stings, though, again, wasps are no more dangerous than bees in that regard. In short, the wasp in the garden or the kitchen or the car should be treated with respect, rather than fear.
“Most people have an unnecessary overreaction to individual wasps,” says Lester, who, in the line of duty, has been stung more than most. “And I think as people get more and more urbanised, that overreaction is only going to increase.” Fear of wildlife is common, he says. “And it’s a bit of a shame.”
WAR ZONES
That said, we are engaged in a war with wasps. In the wild, wasps attack the hatchlings or nestlings of native birds. And they cause havoc in built-up areas, too.
In Nelson, a man who had discovered a nest of wasps in the roof cavity of his home decided to get rid of the pests himself. Using a can of CRC contact cleaner and a cigarette lighter to ignite its spray, he set fire to the nest, but part of his roof went up, too.
“He mostly took care of the wasps,” said a firefighter after saving the man’s house, “but there were still wasps around.”
The death toll of bird hatchlings and the story of the Nelson man illustrate both the scale of the threat to our biodiversity and our somewhat hopeless efforts to do much about the pests.
In his book The Vulgar Wasp – the title comes from the scientific name of the common wasp; vulgaris is Latin for “common” – Lester puts the case clearly.
The million hectares of honeydew beech forest in the northern half of the South Island are home to the world’s highestknown density of wasps, both common and German. And they are extremely voracious hunters and gatherers. They will eat 1.5-8kg of bugs per hectare of forest each year – about the same as the insect-eating birds, including the tiny rifleman, fantail, whitehead and the threatened yellowhead.
Wasps love sugar, too. And these forests are filled with native scale insects – sometimes more than 1500 of them per 1sq m of tree bark – that produce an abundance of sweet, sticky honeydew, a protein source for native fungi, microbes, insects and birds. But here, too, wasps want it all.
“We know that the No 1 threat to birds is introduced mammals,” Lester says. “But we also know, even from anecdotal evidence of people down in places like the Nelson Lakes region, that our native birds are hungry.
“If you put out sugar water, the birds will come to it. If wasps are controlled in an area and you put out sugar water, the birds won’t come, because they’ve got enough to eat. There’s enough of that sort of experience to make us think wasps are a big problem for our birds.”
With wasps taking 99% of available honeydew in the beech forests and also consuming as much biomass as all of the resident native birds, it seems almost certain, Lester says, they have contributed to the population decline of a range of birds in these forests. You only have to stand and listen to know it’s true, he says.
“You go down in those forests and walk a track at this time of year and you don’t hear the birds; you hear the drone of wasps. Those forests are wasp factories.”
Invasive social wasps sting the country, and the greatest single burden is carried by our apicultural industry.
THE BEEKEEPERS’ BURDEN
It isn’t just our birds; it’s our bees. Invasive social wasps sting the country, and the greatest single burden is carried by our apicultural industry. Of the estimated $133 million a year that wasps cost the economy, half falls on beekeepers.
According to a 2015 report for the Department of Conservation and the Ministry for Primary Industries, the bulk of that cost is in lost opportunities: wasps consume nectar and honeydew that, if collected by bees, would generate $57.8 million for the honey industry. On top of this forgone revenue is another $8.8 million in direct costs
to beekeepers of hives lost to wasps and of time, money and effort expended on wasp management. That $66.6 million loss is equivalent to 20% of the 2016-17 revenue from honey exports.
Nationally, about 5% of hives are lost to wasps each year, but beekeepers in areas with the highest concentrations of wasps report losing up to a third of their hives.
Lester says he’s watched wasps select their prey. They will pounce and dismember the bee, quickly removing first the head and then the wings and sometimes other body parts, before taking the treat back to their nest.
It seems wasps can determine which is the weakest and most poorly defended hive in an apiary and then launch an allout assault that may last days. Once that hive is destroyed, the wasps find another weak hive and the destruction begins again.
In zones where wasps abound, bees
Wasps dismember the bee, removing the head, the wings and sometimes other body parts, before taking the treat back to their nest.
devote more time and energy to protecting their hives: fewer bees pollinate the clover that, through nitrogen fixing, makes for healthy pasture. To make up the shortfall, farmers use nitrogen fertilisers. It’s estimated that, in this way, wasps cost agriculture $62 million each year. If they disappeared, a lot less fertiliser would be needed, and less of it would leach into streams and waterways at the expense of the environment.
In short, wasps cost us money, lots of it. By 2050, it may have amounted to as much as $2 billion.
CHEMICAL WARFARE
As killers, wasps have nothing on humans. Yet our efforts to control these invaders, let alone eradicate them, show how impotent we can be.
The Catholic Church once excommunicated insect pests including the wasp, though they didn’t seem to notice. In 1948, soon after the German wasp invasion, the Government offered a reward of threepence (about $1.50 today) for every hibernating queen sent to the Department of Agriculture. Some 118,000 queens were sent in
– 7000 reportedly caught by one schoolboy – but it wasn’t enough.
In the 1950s, the new pesticide DDT killed wasps, but it killed everything else, too. Soon enough, the chemical was found to be an environmental toxin, so we developed other pesticides. The most common are the neonicotinoids, which are controversial because of their possible effect on honey bees: a number of studies have linked neonicotinoid pesticides to colony collapse disorder.
The only effective chemical control for Vespula wasps that has little effect on honey bees was developed in Nelson. In the early 2000s, a Nelson ecologist, Richard Toft, and others began testing an insecticide called fipronil, which was eventually developed into a bait brand-named Vespex. It works. One DoC biologist compared it to turning on a switch: one day you’ll hear the hum of wasps; the next, bird song.
It isn’t a complete solution. It’s not available at the hardware store – you have to be, or employ, an approved user, and training is required. The use of Vespex still means introducing poison to the environment and it is impracticable and unaffordable to put Vespex bait stations throughout the million often-rugged hectares of our honeydew beech forests. Furthermore, wasps will reinvade areas where Vespex has been used and many pests quickly develop resistance to pesticides.
The best hope for truly controlling Vespula wasps may be just around the corner, but it may well prove to be the most controversial solution yet: two major approaches using genetics are being developed.
The first, called “gene-silencing”, isn’t genetic modification in the traditional sense because it doesn’t alter or affect DNA, but works through destroying targeted ribonucleic acids. This “silences” or inhibits expression in targeted genes, such as those involved, say, in insect skeletons, hormones and digestive processes. It’s highly specific and has been called the next generation of insecticides – but it’s still on the drawing board.
The second approach, called “gene drives”, is most certainly genetic modification, but it holds the greatest potential for controlling wasps and other pests such as malaria-carrying mosquitoes, Lester believes.
The science is complex, holds risks and is untested, but gene drives could overrule the normal laws of inheritance and mean potentially we might manipulate a gene’s expression so that no male wasps are produced.
The mere mention of genetic modification will have some frothing with anger and fear. However, Lester is not only optimistic gene drives will work, but also optimistic that the New Zealand public will accept them.
“I suspect over the next decade or two we are going to see a shift in the public’s attitude towards genetic modification, because of the health benefits for people,” he says.
“We can get rid of a whole bunch of diseases. People see that benefit. I think when people learn a little bit more about the technology, and once we know more about the risks and benefits and have some history behind us, attitudes might start to change.”
The technology won’t come cheap, but the potential cost is in the millions rather than the hundreds of millions. Lester thinks developing gene drives to eradicate the pest is affordable.
LIVE AND LET LIVE
But should eradication be our aim? The Vulgar Wasp is a lively attempt to get those outside science, conservation and government talking about wasp control and such potentially controversial and potentially powerful developments as gene drives. And it challenges us to think about the fundamental questions raised by exterminating pest species.
About 6% of us suffer from entomophobia – a fear of insects – and most of the rest of us hate Vespula wasps just because they’re wasps. But there are those who say we should learn to live with them.
After Lester took part in a Victoria University-sponsored “War on Wasps” campaign a couple years ago, it was pointed out to him by some, including conservationist Andy Blick, that such campaigns accentuate the negative and ignore the positive.
Wasps do some good: they pollinate as they roam in search of food and, in preying on other insect pests, they “cover the forest in their protective cloak”, Blick told Lester.
David Theodoropoulos, author of Invasion Biology: Critique of a Pseudoscience, argues that there is no ecological rule that says the distribution of species must remain stationary.
Lester can see Blick’s and Theodoropoulos’s points. But he also sees the damage that wasps do to our biodiversity. To preserve native species for future generations we must act now, he says – but not without first gaining the public’s support.
“I would like to see more data collected on things like gene drives. We need to go down a road of saying, ‘This is the potential of this control technology. Here are the risks and rewards’.
“And then I agree with Andy Blick: it shouldn’t be me who is making the decision about implementing gene drives or any other control. I think I should be part of the discussion; I know wasps reasonably well. But I don’t think I should be the person who is judge, jury and executioner. It has to come from a much wider group than just me. It has to come from New Zealanders.”
The Catholic Church once excommunicated insect pests including the wasp, though they didn’t seem to notice.