On Christmas Island, Parks Australia and La Trobe University have worked towards a new way of controlling invasive yellow crazy ants, by using indirect biological control (also called ‘biocontrol’).
What does biocontrol mean?
In this case, it means using another insect to target the crazy ants’ food source, as a way of cutting down their numbers and stop them causing so much environmental damage, especially to iconic red crab populations.
In this case, the biological control agent that we want to use is a tiny insect called a micro-wasp.
Why is biocontrol needed on Christmas Island?
The success of this project should reduce the need for poison baiting to control the ants. Poison baiting is expensive, short term and unpopular with local residents, but it has been the only available and feasible option control the ants.
Micro-wasps are already used for biological control on mainland Australia, so this approach is fairly common. We’re a long way from the days of the cane toad, which was released in Australia with very little scientific testing. These days biological control is carefully planned and managed.
How the biocontrol project will work
A tiny Malaysian insect called a micro-wasp will be brought onto Christmas Island by scientists from La Trobe University. It is 2 mm long and its formal name is Tachardiaephagus somervillei.
The micro-wasp doesn’t sting or build nests and it doesn’t harm humans, native wildlife or horticulture. Many similar micro-wasps already live on the island, but are rarely noticed.
Scientific studies indicate this biocontrol micro-wasp will stop crazy ants by cutting down their food supply, honey dew, which is produced by another non-native species, the yellow lac scale insect.
The micro-wasp kills the lac scale insect by laying eggs inside it. The micro-wasp is extremely ‘host-specific’. This means it only preys on one thing – the particular species of lac scale insect on Christmas Island – so it doesn’t harm anything else.
There are already strict quarantine protections in place which prevent insects from reaching the Australian mainland from Christmas Island. Parks Australia, which manages Christmas Island National Park, is funding the project and is jointly managing it with La Trobe University.
Rangers and scientists will rear the micro-wasps and then release them into ‘super-colonies’ of crazy ants. The results will be carefully monitored to see how the crazy ants react to a reduction in their food supply.
Over time, we hope to see crazy ant numbers fall so much that they no longer form destructive ‘super-colonies’ made of billions of ants, which are causing so much damage.
The crazy ant problem
Crazy ants are an introduced species that are hugely destructive to the environment on the island. Over recent decades, they have killed tens of millions of Christmas Island’s iconic red crabs.
Until now, the only way to stop crazy ants wiping out Christmas Island’s wildlife was to use poison bait. Rangers from Christmas Island National Park have to lay the bait in the dense ‘super colonies’ that swarm with billions of crazy ants, using a mix of hand delivery and aerial baiting from a helicopter.
While this baiting is effective, it is only a temporary solution. The crazy ants move back in from remote and inaccessible parts of the island, and within a few years more baiting is needed. This is expensive, labour intensive and the use of poison is unpopular amongst local residents.
Parks Australia and Christmas Island National Park have been working on a better solution. Since 2009, Parks Australia have partnered with La Trobe University to investigate the use of a ‘biological control agent’ – to work out if there were any animals that could help us control the crazy ants without having any negative impacts on Christmas Island or its environment.
The scientists are confident this micro-wasp biocontrol solution will be safe and effective on Christmas Island.
Assessment by the Department of Agriculture and Water Resources
The Australian Government Department of Agriculture and Water Resources has carried out a risk analysis for the release of Tachardiaephagus somervillei on Christmas Island for the control of the invasive scale insect Tachardina aurantiaca.
After a thorough risk analysis the Department of the Environment and Energy recommended that the Minister add the control agent to the list of approved live imports.