Micro-wasps take on crazy-ant colonies

A tiny wasp on Christmas Island is showing signs of success in tackling one of the world’s worst invasive species.

Over the past 18 months the Malaysian micro-wasp Tachardiaephagus somervilli, just 2mm in size, has been employed by researchers as a biological control method to curtail the spread of yellow crazy ants.

The wasps were placed in yellow crazy ant super colonies in Christmas Island National Park, and so far the wasps have survived and spread from their released sites.

Parks Australia and La Trobe University worked on an elegant solution to dramatically reduce crazy ant numbers without resorting to toxic baiting methods. This followed years of research and in December 2016 the wasp was brought to the island. This solution pits the wasp and crazy ant against each other for the same food source.

The ants have had a devastating impact on the Christmas Island’s keystone wildlife species – the red crab - and despite years of expensive baiting regimes the ants continue to damage the island’s wildlife and ecosystem.

Parks Australia’s acting Director of National Parks Judy West said this new approach to controlling one of the world’s most invasive species was on track.

“The results of recent surveys show the wasps have survived in the trees above yellow crazy ant super-colonies and been able to spread up to 1.6 km from release areas,” she said. “It will be some time before we see a reduction in crazy ant numbers but major steps in that direction are being taken.

“The wasp doesn’t attack the yellow crazy ants directly, it parasitises and kills the lac scale which produces honey dew – the crazy ants’ main food source. The lac scale insect is another introduced species that impacts flora on the island.”

The wasp does not sting or build nests and does not harm people, pets, plants or other wildlife.

La Trobe University ecologist Dr Pete Green said the biocontrol project was showing positive signs.

“This is as good as we could have hoped for and means our biological control agent is spreading under its own steam, as we’d planned,” Dr Green said. “The wasps have established in the wild more than one-and-half kilometres from release sites.

“From the initial 340 micro-wasps imported to the island, we’ve bred and released 18,000 across four crazy ant super-colony sites at Grants Well, Blowholes, Margaret Knoll and Circuit Tracks.

“Although signs are promising, it will still take many months before the wasps have a significant impact on the lac scale insect. Once the wasps have significantly reduced the lac scale insects, we expect to see a drop in crazy-ant numbers.”

The yellow crazy ant is among the world’s 100 worst invasive species according to the International Union for Conservation of Nature. Parks Australia and La Trobe University have spent
years carefully planning the implementation of the biological control project to ensure it had the best possible chance of success.

Since the ants began forming destructive super-colonies 20 years ago, they’ve killed tens of millions of red crabs and taken over large parts of the island’s forests.

Although biological control is a novel approach for Christmas Island, it is not new for Australia. In more recent times it has used to solve many of Australia’s pest problems. This includes biological controls for the prickly pear, mimosa plants and salvinia.

An effective biological control will significantly reduce the costs of yellow crazy ant management while minimising the impact they have on the island’s land, animals and communities.

A side-benefit of the introduction of the micro-wasp could be to improve horticulture by controlling the lac scale insects which attack fruit trees and other plants on the island. The lac scale insects also kill large forest trees and smother the understory with sooty mould. With a reduction of the lac scale the entire forest ecosystem may get a reprieve.

Media contacts:

Mark Sawa - Parks Australia media manager – 02 6274 1276 or 0416 911 968

Anastasia Salamastrakis – La Trobe University senior media officer – 03 9479 6565 or 0437 457 780

Photo credit - Parks Australia