Conservation Comment: Wasps are a serious pest

A German wasp: catastrophic pest. Photo/file

Wasps are a problem.

Although most of the conversation about controlling invasive species is fixated on mammals -- rats, stoats, possums -- we should be taking wasps just as seriously.

Wasps cost New Zealand agriculture $130 million a year, by attacking hives, robbing bees of nectar, and disrupting clover pollination. They regularly attack people, injuring and sometimes killing them.

Tourists don't want to visit a national park full of aggressive wasps.

And, most significantly, they have a huge effect on native species. Wasps don't just steal the beech honeydew that birds like kaka need to survive, they eat staggering numbers of insects upon which the entire forest ecosystem depends, and even attack and kill baby birds in the nest.

In April, I attended the Entomological Society of New Zealand conference, and heard from researchers looking at ways to control German and common wasps, our worst insect pests. New Zealand has the highest densities of these wasps in the world, and in our beech forests the total mass of wasps exceeds that of birds, rats, and stoats combined.

One promising control tool is Vespex, invented in New Zealand. This poison is delivered in a protein bait, so it's not attractive to bees and can be safely used around hives. After a decade of trials in the Nelson area, it seems to have no side-effects on the forest ecosystem.

It only works during the few weeks in summer when wasps are foraging for protein, but can reduce their numbers by 95-100 per cent. Vespex bait stations need to be set by hand, so it is only practical to use in small areas: DOC simply doesn't have the funds and staff to set up a 200 m grid of bait stations across the entire New Zealand bush.

Because of Vespex's limitations, scientists are looking at other strategies. New Zealand's wasps have very few of the diseases or parasites found back in their native Europe, so biological control is one option.

The tiny wasp-parasite Sphecophaga was introduced in the 1980s, but it had little impact. Those Sphecophaga were taken from mainland Europe, though, not the southwestern UK where our wasps came from, and a batch from Britain is currently in quarantine awaiting another trial.

There are other candidates, too: two fly species, one of which attacks adult wasps and the other their larvae, as well as a beetle that eats wasp pupae. Years of testing will be needed before they can be released, though.

Another control option is to manipulate the wasps' genes. It's theoretically possible to create a "Trojan female" wasp, a queen carrying a gene that will make her male offspring sterile. Another option is to create genetically-modified wasps that, through a process called "gene drive", only produce male offspring, wiping out a population in one generation.

Both these processes are only theoretical, and don't even work properly in the lab yet. The research effort required to engineer and breed thousands of transgenic wasps is mindboggling to contemplate, and the scientists involved say it will be decades before these technologies could be deployed.

In the meantime, we do what we can. This summer I'm becoming a certified Vespex user, and will be volunteering to set up bait stations in local forest reserves.

We can all monitor wasp nests in our neighbourhood and (safely!) eradicate them. And we can support, with our taxes and our votes, the entomology research that will one day fix New Zealand's wasp catastrophe.

Dr Mike Dickison is curator of natural history at the Whanganui Regional Museum