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Winning the battle against the invasive yellow crazy ants

As South Australia struggles with the scourge of the invasive fire ant, plans are being made on the other side of the country to eradicate another ant within a decade.

The Wet Tropics Management Authority (WTMA) in Far North Queensland reports that yellow crazy ants (Anoplolepis gracilipes) have been eradicated from an additional 365 ha (900 acres), which they say is “the largest eradication of this pest ever documented in the world.”

Scott Buchanan, the Authority’s executive director, is optimistic about the eradication programme, saying: “The threat from these ants cannot be overestimated.

“I am confident that…we can eradicate them from the World Heritage area within ten years.”

Yellow crazy ants are believed to originate from Southeast Asia. They were first discovered on Australian territory on Christmas Island in 1934, and have since spread to the Northern Territory and along the east coast of Australia.

The CSIRO has also had success with its crazy ant eradication program and says it has eliminated them from 26 sites in north-east Arnhem Land in the Northern Territory.

The WTMA says they are one of the 100 worst invasive species in the world.

“The invasive potential of yellow crazy ants stems from their ability to work together,” said an authority spokesperson.

“Unlike many native ants, the species is polygynous, meaning nests can contain multiple queens, and nests work together rather than compete for resources. These networks of interconnected nests, or supercolonies, can stretch across entire landscapes and harbor millions of ants: more than a thousand ants per square meter.

“The ants spray formic acid as a defense mechanism and to subdue prey, and the effects on native wildlife can be devastating. At supercolony densities, the swarming, acid-spraying ants pose a formidable threat to other invertebrates, as well as reptiles, amphibians, baby birds and anything else that can’t escape.

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“When a plague spreads, larger or more mobile rainforest species such as kingfishers, tree kangaroos and even cassowaries are forced to move. Without their native species, the rainforests of the Wet Tropics fall eerily silent.

“The ants also protect scale insects by ‘farming’ them for sweet honeydew. These scale insects promote sooty mold on plants and crops, reducing agricultural productivity.”

Fieldwork sites in the Wet Tropics include agricultural pastures and suburban properties to steep, mountainous jungle and rocky gullies.

Scent detection dogs, scientists and ecologists map the movements of the ants.

When contamination is identified, the Authority uses fipronil with an active substance of 0.01 g/kg in a fishmeal bait matrix. The bait is applied at a rate of 5 kg/ha, or only 0.05 g of insecticide per hectare.

“If we apply too high a dose, the ants will die before they can return to the nest and share it,” said Gareth Humphreys, technical team leader of the Yellow Crazy Ant Eradication Program.

“It is a significantly lower dose than commonly used to treat termites, or fleas and ticks in pets. We are continuously testing the soil and water in the treated areas and have not detected any fipronil, so we are very pleased.”

Historically, the Authority has dealt with major infestations by helicopter. Hand treatment is applied to small or sensitive treatment areas. Recently, the team also began using drones for treatment in areas not suitable for helicopters or boots on the ground.

Using mold to eradicate crazy ants?

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