Tawny crazy ants (Nylanderia fulva) are native to South America but have become an invasive pest in the United States. The first record of tawny crazy ants in this country was recorded in Brownsville, Texas in 1938, and since then the species has spread to every Gulf Coast state in the United States. This invader occurs in colonies that span huge numbers of individuals and cause the destruction of local insect communities and the consternation of residents of urban areas where it has established itself.
Called “crazy” because of its quick and unpredictable movements, this species of ant nests in almost any hole, nook or cranny it can find. In urban areas, tawny crazy ants often nest in electrical equipment, such as pump sets, electrical distribution boxes or fuse boxes. This can cause short circuits and failure of electrical equipment. The ants displace local ants and other insect species and are not easily treated with pesticides. Each colony has multiple queens, so eradicating an entire colony is nearly impossible.
Scientists at the University of Texas at Austin have been studying tawny crazy ants for the past few years and have made an encouraging discovery. They have discovered that a natural fungus is parasitizing these ants and can lead to the reduction or total disappearance of ant populations. The results of their study are published today in the journal Proceedings of the National Academy of Sciences.
“I think it has a lot of potential for protecting sensitive habitats with endangered species or areas of high conservation value,” said Edward Lebrunresearcher at the Texas Invasive Species Research Program at Brackenridge Field Laboratory and lead author of the study.
Ants have been sounding the alarm in the southeastern United States for the past 20 years as they have spread from state to state. They are inadvertently transported by animals, vehicles and humans – for example in waste and on plants that are transported from one site to another. They totally overwhelm local insect species and are also known to seek moisture in the eyes of mammals and birds.
LeBrun and his colleague Lawrence Gilbert, also of the Brackenridge Field Laboratory, collected tawny crazy ants from Florida about eight years ago and noticed that some of them had swollen abdomens with fat. When they looked inside the ants, they found spores of a microsporidian fungal pathogen and identified a species of this type of parasite that was new to science. Microsporidian pathogens typically hijack an insect’s fat cells and turn them into spore factories for their own benefit.
Although the researchers were unsure where the pathogen came from, or if it might have been native to the home range of ants in South America, they began to notice that ants infected with the fungus were found at sites across Texas. By observing 15 local populations over eight years, the team found that every population that harbored the pathogen had declined – and 62% of those populations had completely disappeared.
This meant that the researchers had inadvertently discovered a natural control method to keep tawny crazy ant populations under control. They wondered if they could use the pathogen to induce population decline in areas where the ants were a pest or destroying sensitive habitats.
“That doesn’t mean crazy ants are going to go away,” LeBrun said. “It is impossible to predict how long it will take for lightning to strike and the pathogen to infect a single population of crazy ants. But that’s a big relief because it means these populations seem to have a lifespan.
“You don’t expect a pathogen to cause the extinction of a population. An infected population normally goes through cycles of boom and bust as the frequency of infections rises and falls. »
Researchers had the chance to test use of the fungal pathogen when LeBrun received a call from Estero Llano Grande State Park in Weslaco, Texas in 2016. The park was infested with tawny crazy ants and was losing its invasive species insects, scorpions, snakes, lizards and birds. Even baby rabbits were blinded in their nests by swarms of acid-spewing ants seeking moisture in their eyes.
“They had a crazy ant infestation, and it was apocalyptic, rivers of ants going up and down every tree,” LeBrun said. “I wasn’t really ready to start this as an experimental process, but it’s like, OK, let’s just try.”
The team used crazy ants they had collected from other sites that were already infected with the microsporidian pathogen. They introduced nest boxes of infected ants near resident ant nest sites in the state park, hoping that the two populations would mix and that the infected ants would carry the pathogen into the resident ants’ nests. The researchers placed hot dogs around the exit chambers to attract local ants and merge the two populations.
The experiment worked spectacularly. In the first year, the disease spread to the entire population of crazy ants in Estero. And within two years, the number of crazy ants crashed. Now they are non-existent and native species are returning to the area. Researchers have since eradicated a second population of crazy ants this way at another site in the Convict Hill area of Austin.
Researchers aren’t sure exactly why ant colonies are collapsing and theorize that the pathogen may shorten the lifespan of worker ants, meaning the colony struggles to collect enough food to survive the winter. Whatever the reason, the fungus seems to only infect crazy ants, leaving other native species of ants and other insects unharmed.
The team plans to test their new biocontrol approach this spring in other sensitive Texas habitats infested with crazy ants.
—
By Alison Bosman, Terre.com Personal editor