World's biggest wasp kill starts

The world's largest wasp kill should wipe out millions of the pest in forest around Lake Rotoiti, near Nelson, this week, the Department of Conservation says.

Each year DoC staff kill wasps as part of the Rotoiti nature recovery project, distributing the insecticide Finitron in bait stations on 1100ha of trees. Foraging wasps take the bait back to their nests, where other wasps eat it.

DoC ranger Matt Maitland said he expected to see a difference in the wasp population this week.

"We anticipate around 70 per cent of the wasps in the operational area will have been killed. That amounts to millions of wasps."

Mr Maitland said New Zealand's honeydew forests held the highest densities of wasps in the world, and they took the honeydew - a rich food source important to condition birds for breeding.

Billions of tiny native sooty beech insects in the lowland beech forests extracted an astonishing 32 per cent of the energy produced by photosynthesis in the trees, by sucking sap from the trees, he said.

In turn, the insects excreted a sugary "honeydew" on which some native animals, including tui, bellbirds, kaka and geckos, depended for a sugar boost to get them in shape for breeding.

But the wasps, an introduced pest, also descended on the honeydew in their millions, collecting sugar for an "energy kick" before hunting for protein by feeding on insects and harassing birds, sometimes killing chicks in nests, said Mr Maitland.

Individual wasp nests could contain up to 100,000 wasps and there were, on average, nine nests to a hectare of beech forest. However, in 1993, a boom year for wasps, there were 17 nests a hectare. In their native Europe, the wasps averaged about three nests a hectare.

Ecosystem models had shown that wasp densities need to be reduced to just two nests a hectare to reduce their negative impacts on native birds and insects, Mr Maitland said.

"Native birds are in the middle of their breeding season, so controlling wasps at this time - along with other pest control - helps ensure successful nesting, which in turn increases bird life in the area."

- NZPA