Halting the spread of the little fire ant

One of the country’s most tenacious pests, it’s almost invisible and its bites are painful and persistent.

EXPERTS AGREE that in Israel the fire ant is spreading primarily through plants in nurseries.  (photo credit: JOE A. MACGOWN/MISSISSIPPI ENTOMOLOGICAL MUSEUM/TNS)
EXPERTS AGREE that in Israel the fire ant is spreading primarily through plants in nurseries.
The little fire ant (Wasmannia auropunctata) has long taken a foothold in the country. Since its discovery in 2005, this tiny resilient insect has spread across large parts of the country and is not only a nuisance to humans but has severe impacts on local biodiversity. The spread has become so problematic that officials of the Environmental Protection Ministry have decided to take new steps to mitigate the infestation.
Studies suggest that the ant arrived here in 1998, but there is no real evidence to confirm that assumption.
Origin unknown
“No one really knows when the invasion actually started, says Prof. Abraham Hefetz, chemical ecologist and evolutionary biologist at the George S. Wise Faculty of Life Sciences at Tel Aviv University. “We discovered the ant for the first time in 2005. Back then, one of my students, who was researching the impacts of invasive ants, found a species she didn’t know during one of her collection trips to the Sea of Galilee.”
At the time, the scientist assumed the ant was brought to Israel from West Africa. However, a collaboration with a French team of scientists who had been studying the small fire ant in different parts of the world established that the little fire ant in Israel actually came from Brazil.
“It is unclear how the ant got here all the way from Brazil, but there is a very good chance that young Israeli backpackers unwittingly brought the ant back home with them. Since South America is a popular backpacking destination for young Israelis after completing their army service, this could be a very tangible possibility,” says Hefetz.
Clones of their mothers
Back then, the scientists collected about 20 eggs from nests in different sides and conducted a molecular study. According to Hefetz, the study findings indicated that all the ant queens that were found in individual colonies are clones of each other.
“The little fire ant has a very peculiar reproductive system. Every queen is the clone of their mother, while all the males are a clone of their father.”
Dr. Eyal Privman, a social insect genomics researcher at the Institute of Evolution at the University of Haifa, explains how the little fire ant reproduces, and if it was not a scientific fact it could have been the basis for a science fiction movie.
“The little fire ant can reproduce, both sexually as well as asexually,” says Privman. “The workers, which are all female, are the result of the normal mating process between a queen and a male. But whenever a queen wants to create a new queen, she chooses to reproduce asexually, meaning she clones herself. Therefore every new queen born in Israel is a genetic replica of the first fire ant queen that was inadvertently introduced about 20 years ago.”
However, according to the scientist, it doesn’t stop there. There are also male ants, which father the workers. But the workers never reproduce. That means the most fundamental aspect of evolution, passing on one’s genes to the next generation, is lost. So how does the little fire ant produce male ants? “This is where it gets really crazy,” says Privman.
“Every male ant is a clone of its father, but since males cannot clone themselves, they need the queen to do it for them. Every male egg that the queen is laying is a genetic replica of the father but contains no genetic contribution from the queen herself. The queen merely facilitates the cloning process of the male. This bizarre reproductive mechanism has evolved only in ants,” he says.
In addition, Privman believes the little fire ant’s advanced social structure might be at the root of the insect’s invasiveness.
“In a typical ant colony, you have one queen, who is the mother of all the workers. That is not the case in the little fire ant. Each nest is home to multiple queens, as well as workers that do not descend from the same queen. Still, they function as a community and collaborate, instead of fighting each other. That is a dramatic difference and could be the reason why this particular species is spreading so rapidly.”
Fighting the little fire ant
According to Hefetz, experts agree that in Israel the ant is spreading primarily through plants in nurseries, a fact that was resoundingly substantiated this year by the Environmental Protection Ministry.
“Since the beginning of the year, we’ve examined almost 100 public and private plant nurseries throughout Israel, and many of them are infested with the little fire ant,” says Dr. Gal Zagron, director of the Pesticides and Pest Control Division at the ministry and an expert in veterinary public health.
According to Zagron, the ministry’s Pesticides and Pest Control Division has made the little fire ant one of its top priorities on this year’s agenda. For that purpose, the department has set up three focus groups solely dedicated to tackling the pest.
“The first team is a review committee in charge of providing the full picture of the state of the infestation; the second group focuses on citizen science and how to get the public and local councils involved, while the third group was tasked with developing the best practice control protocol for the little fire ant,” Zagron says. To meet their objectives, the ministry is collaborating with the Natures and Parks Authority, the Entomological Laboratory for Applied Ecology at the Steinhardt Museum of Natural History in Tel Aviv and the Society for the Protection of Nature in Israel (SPNI).
“Together with the SPNI, we’ve created a citizen survey, designed to engage the public in the fight against the little fire ant. It’s a simple form that anyone who’s sighted a nest or hot spot can fill out. The observations are recorded on a visual map that is open to the public. Of course, we have to confirm these sightings, but it is extremely helpful in the work we do,” says Zagron.
One of the reasons the ministry is looking to involve the public in their efforts is to find out about new sightings in places that have no history of infestation as early as possible. “The younger the infestation, the easier you can get rid of it,” says Zagron.
Working with local councils
This year, after discovering that public and private plant nurseries are the main sources of the ant infestation, the ministry has started to take a closer look at the local councils to get a better understanding of the pathway of the spread.
“We’ve looked at all the local councils and realized that in the same council you have the people that are in charge of the public green spaces, and those who are responsible for the control of substances hazardous to health. Many times these branches do not communicate properly. What that means is that on the one hand, you have the public gardeners who inadvertently spread the ants from the nurseries, while on the other hand, you have the people who are spraying the insecticides because they are getting all the complaints from the citizens who are getting bitten. Realizing this problem was a major breakthrough for us this year,” says Zagron.
According to Zagron, finding the infected nurseries is not always easy. Many of them are used exclusively by local councils and do not sell to the public, so they are not registered as businesses. Even those municipalities that do not have their own nurseries most likely contribute to the spread since they buy from other large nurseries.
“That’s why, in the next step, we will approach all the local councils whether they have their own nurseries or not and help them address this problem in their jurisdiction.”
But even if an infestation has been detected, controlling the spread of the ant in the nurseries is very difficult, as the bait that contains the insecticide must be put in a dry place.
Plant nurseries, however, are generally very wet. “The way this works is that the insecticide is concentrated in little grains that exterminators scatter in different spots of a nursery. The ants come, pick up the grains and carry them back to the nest where they kill off the colony. But if the grains absorb too much moisture, they become too heavy for the ants to carry, and they will just take something else instead,” explains Zagron. “So in most cases, we have to come back more than once to check if the bait has been effective.”
Zagron also adds that simply spraying an entire nursery with a chemical is ineffective as it doesn’t target the nest itself. As long as the nest is still intact, the ants can recover and come back.
A late response
“All in all,” says Zagron, “we’ve done a lot of work on the small fire ant this year. Not only did we update our guidelines in order to get the local authorities to step up and face this problem in their nurseries, but we’ve located many areas of infestation and began developing methods to deal with it. In addition, because the spread has taken on such a dramatic scale, we are planning not only to target nurseries like we did until now but also public spaces in collaboration with the local authorities,
“Unfortunately, we didn’t react fast enough in the past, and now, the spread has probably come too far to destroy it entirely. Yet, it’s not hopeless. We are confident that with the right measures and the continuous effort of the Environmental Protection Ministry, the local authorities and every other institution involved, it is possible to control and even curb the spread of the little fire ant,” Zagron says.