Winning the battle against yellow crazy ants

Cosmos Magazine


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By Cosmos

As South East Queensland and small parts of New South Wales grapple with the infestation of the invasive fire ant, at the top end of the country plans are underway 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 a further 365ha (900 acres), which it says is :”the largest eradication of this pest ever documented in the world.”

Scott Buchanan, Executive Director of the Authority, is optimistic about the Eradication Program, and says: “The threat from these ants can’t be overestimated.

“I’m confident that…we can eradicate them from the World Heritage Area within 10 years.”

Yellow crazy ants are believed to be native to South-East Asia. They were first detected on Australian soil at Christmas Island in 1934, and since then they’ve spread to the Northern Territory and down Australia’s east coast.

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

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

“Yellow crazy ants’ invasive ability stems from their cooperative capacity,” a spokesperson for the authority says.

“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 super colonies, can extend across entire landscapes and harbour millions of ants—over 1000 ants per square metre.

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

“When an infestation takes hold, larger or more mobile rainforest species such as kingfishers, tree-kangaroos and even cassowaries are forced to move out. Without their native species, the Wet Tropics rainforests fall eerily silent.

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

Field work sites in the Wet Tropics include agricultural paddocks and suburban properties to steep, mountainous jungle and rocky gullies.

Odour detection dogs, scientists, ecologists plot the ants’ movements.

Where an infestation is detected, the Authority uses a fipronil at 0.01g/kg of active ingredient in a fishmeal bait matrix. The bait is applied at 5kg/ha, or just 0.05g of insecticide per hectare.

“If we apply too high a dose, the ants 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’s a substantially lower dose than is commonly used to treat termites, or fleas and ticks on domestic pets. We continually test soil and water in the treated areas and have not detected fipronil, so we’re very satisfied.”

Historically, the Authority has treated large infestations by helicopter. Hand treatment is used in small or sensitive treatment areas. Recently, the team also began using drones for treatment in areas unsuitable for either helicopters or boots on the ground.

Using fungus to eradicate crazy ants?

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