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The Conversation

Maui crews are successfully eradicating invasive little fire ants — with aerial support

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Hawaii Department of Agriculture
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Little fire ants

There’s a bright spot in the battle against the little fire ant on Maui. Crews have been successfully eradicating the ants from dense vegetation and difficult terrain.

The Maui Invasive Species Committee began a pilot project two years ago using helicopters to spray bait aimed at sterilizing ant queens and curbing the stinging pests. The spray combines food-grade ingredients and a growth regulator that acts like birth control for the queens.

Fire ant coordinator Brooke Mahnken and education specialist Serena Fukushima said they were happy to share some good news — the project was able to continue throughout the pandemic.

"We were able to continue pretty much uninterrupted. We did 13 treatments, roughly six weeks apart starting in October of 2019 all the way up to May of 2021," Mahnken said. "We needed to go out and conduct a survey to be able to assess how the treatments have been working — and that is no small feat."

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Maui Invasive Species Committee
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MISC prepares helicopter applications of ant birth control in the dense jungle of Nāhiku.

The survey area in Nāhiku is about 175 acres and ranges from sea level up to 1,200-foot elevation — and it's in the rugged East Maui watershed, he said. The infestation in that area was first discovered in 2014.

"If you look at a map, the infestation is linear. It's very long, almost two miles long. What we believe is that they were introduced mauka, around 1,000 feet at a residence, and the infestation spread and got to the stream and then was washed downstream, all the way to the ocean," he said.

Crews have been navigating dense rainforests, vegetation and rivers to search for the ants after treatments.

"We got about three-quarters of the way done. We just need to go in and fill in some of the gaps. But what we're finding is over 3,000 samples, 95% of those samples came back with no ants at all," Mahnken told Hawaiʻi Public Radio.

He said there are very few little fire ants left, and they're located in one small portion. So they plan to redraw the aerial treatment area and continue treatments there.

"Overall, the change has been very, very big from the infested area before to what it is now," he said. "There are places where you couldn't really practically use a helicopter, of course, and that's around people, houses, etc. And so that's also often where the little fire ant infestations show up."

"But for large natural areas, using a helicopter would really change the game for little fire ant control, particularly for some of the other islands. On Maui, this is our largest infestation and we're hammering away at it and things are going well so there's not a great need for helicopter work here on Maui beyond that — but the other islands could really use the help at this point," Mahnken said.

"Majority of our population reports for little fire ants here on Maui have been reported to us by the community. So it's really important that if people are having suspect ants in their area, if they are getting stung by ants, that they report it over the MISC," education specialist Serena Fukushima said.

Free ant collection kits, and the portal to report ants, can be found at stoptheant.org. This interview aired on The Conversation on Oct. 28, 2021.

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