|Photo: Alex Wild|
In 2016, staff at Estero Llano Grande State Park knew something wrong. During night tours for visitors, they noticed many of the normally-seen species like scorpions were gone. They also had not seen many snakes or lizards common to the area. Then came sightings of blinded rabbits.
Turns out that this state park’s native species were being overrun by tawny crazy ants (Nylanderia fulva), an invasive ant native to South America. Tawny crazy ants not only wreak havoc on native species and biodiversity, but they also cause enormous amounts of damage to human-built structures. They can accumulate in buildings and short circuit electrical connections. They are also nearly impossible to eradicate via normal pest control methods.
Hoping to find help, Estero Llano Grande State Park reached out to Brackenridge Field Lab (BFL). As it was, the researchers at BFL were in the process of thinking about a biological control agent for these ants. The BFL researchers had discovered a disease on this ant, a microsporidian, in 2015 and early work funded in part by TPWD indicated it had promise as a control agent.
|"One is a nest entrance of seed harvester ants being raided by tawny crazy ants. To keep the tawny crazy ants out of their nest, the seed harvester workers (large red ants) on the outside have sealed the entrance to their colony’s nest. They can only do this by dropping in pebbles from the outside. They are now trapped outside. If the tawny crazy ant workers do not finish them off, the heat of the day will. Suicidal altruism." - Research Scientist, Ed LeBrun (Photo: Rob Plowes)|
Microsporidia are pathogens of primarily insects and fish. They are fairly specific pathogens that will attack a group of closely-related species. They are related to fungi, and have a virus-like life history. They have a spore phase, just like a fungus. When the host ingests a spore, the spore is able to differentiate its host from others. When it arrives in the gut of its host, the spore releases a polar filament. A polar filament is a tube that has a harpoon tip. When it fires out, it penetrates the cell wall of the host. Here they inject the contents of their spore cell down the tube and into the host’s cell. From this point, they are an intracellular pathogen. They hijack the host’s cell machinery to make more copies of themselves.
In the crazy ant, microsporidia hijack the fat cells and turns them into sporocysts.
So BFL researchers decided to experiment using this pathogen to combat the tawny crazy ants at Estero. The impacts on local biodiversity in this park were not going to change without immediate intervention. As luck would have it, the researchers had located this pathogen here in the US, in populations in Texas and Florida. Since it was already in the environment, they would not have to go through the normally time-consuming process of laboratory biology to document safety before releasing it outside the lab. To start, the BFL researchers would set up two different inoculation sites at Estero.
But how does one go about inoculating ants? The answer starts with a key feature of this species. Tawny crazy ants are super colonial. They do not have nuptial flights where a new queen will depart her home colony to begin her own, which is how some ants start new populations. Tawny crazy ants spread by nest budding. The population as a whole is an interconnected network of nests that can be several kilometers in diameter, with no intrinsic upper limit on how big they can grow. The population might be separated by, for example, new construction of a road or building, but when these ants are reunited, they recognize each other. They don’t fight, they cooperate.
|This is a White-winged dove fledgling, being consumed by tawny crazy ants. These nestlings are often driven out of the nest by irritation from being swarmed by ants prior to their being able to fly. (Photo: Larry Gilbert)|
Most likely due to a single introduction, this means all the ants in Texas as well as Florida are members of the same colony, broken apart by human activity. In theory, this interconnectedness should simplify inoculation. The researchers should just be able to take infected ants and watch the disease spread through introduction of multiple infected colony fragments containing many workers, brood and queen.
It is actually more difficult in practice. There is a 30-40 percent success rate. So, the chances for the experiment at Estero to work were low. It was possible that local biodiversity there would continue to suffer.
However, that would not be the case, fortunately. In part two of our blog series, we will show how the BFL researchers got control over this tawny crazy ant population.
Thanks to Ed LeBrun, Research Scientist at BFL, for his assistance with this article.