Destroying crazy ant nest structure makes them vulnerable to pathogens

Aggressive tan crazy ants are wreaking havoc along the U.S. Gulf Coast from Florida to Texas, disrupting ecosystems and causing headaches for homeowners. Now, scientists at the University of Texas at Austin have developed a reliable way to introduce a natural pathogen into colonies so that local populations of tawny crazy ants disappear and other native species can recover.

IN recent article V Journal of Animal EcologyThe researchers describe key insights they gleaned from laboratory studies that helped them refine their methods.

More than a decade ago, researchers at the UT Invasive Species Laboratory discovered that some tawny crazy ants in Florida were infected with a naturally occurring pathogen called microsporidia. This pathogen reproduces inside the cells of tawny crazy ants and can only be transmitted when an adult is infected. worker the ants take care of the developing larvae. This also leaves local ants and other arthropods are not harmed, making it an excellent candidate for biocontrol agent.

Tan crazy ants form supercolonies, with all insects in the southeastern United States sharing the same supercolony genetic identity. Crazy ants from anywhere in the region will accept workers from anywhere in the world into their nest as colony mates. In principle, transmission of this disease between infestations should be as simple as introducing live infected workers from a distant infected local supercolony to an uninfected local supercolony.

Problems with pathogen spread

However, the researchers were faced with a mystery. In practice, their attempts to introduce the disease to uninfected populations of crazy ants in nature often failed, whereas in the laboratory the method always worked.

Ants use social immune behavior to prevent the spread of soil-borne, insect-killing and externally infecting fungi to nest neighbors. Lebrun and his fellow researchers theorized that crazy ants used this behavior to prevent infected workers from reaching the colony core and caring for the larvae. They suspected that the complexity of natural nest architecture was a key difference in virus transmission between laboratory and field nests.

Nest space organizes ant colonies, allowing them to separate workers specialized in individual tasks, such as brood care, carcass removal, or foraging, into separate zones. This spatial segregation of workers may allow social immune behavior to isolate sick individuals to the periphery and prevent disease migration into the colony core.

A simple test confirmed this concept. Colonies occupying multi-chamber nests were able to prevent infection from entering the developing brood, while colonies in standard single-chamber nests were not.

“This is the first demonstration that in ant societies, the spatial structure of the nest is of utmost importance, allowing social immune behavior to prevent disease from entering the colony core where the queen and brood live,” said Edward LeBrun, a postdoctoral fellow in the Department of Integrative Biology at the University of Texas at Austin, who led the study. This demonstrates the effectiveness of “architectural immunity.”

Ant behavior and disease prevention

Further work identified the behavioral mechanisms involved. Infected and uninfected crazy ants placed in a colony behave differently. Infected crazy ants introduced near the queen migrate to the periphery of the nest, taking on the tasks of carcass removal and foraging, while uninfected individuals remain near the core of the colony. Subsequently, infected individuals isolate themselves, avoiding groups of other ants.

Aggressive interactions also occur between infected and uninfected crazy ants. Potentially, uninfected ants will recognize the infection. This apparent self-sacrifice can be partly controlled by the employees of the enterprise. colony basic. In addition, infected workers preferentially remove the carcasses of other infected ants, preventing uninfected ants from coming into contact with the infectious agents.

Many of these behaviors have previously been observed in ants defending themselves against fungi that infect them from the outside. However, this is the first demonstration that supercolonial invasive ants also use this behavior and that it is useful against a wide range of pathogens. Similar to the types of quarantines and social distancing policies that human societies use to limit pandemics, ants have a conservative set of behaviors that they use to protect themselves from pathogens in general.

Improving Strategies for Local Success

The results of this work have changed the way the team tries to introduce the pathogen into uninfected crazy ants in the wild. Previously, infected ants were introduced onto the paths of ants feeding on food resources or directly into nests, but with caution so as not to damage the host nest. Now they are doing the opposite.

“The way we do it now is we destroy the nest—we just tear it apart—and then introduce the infected ants,” LeBrun said. “So all the ants get mixed up and they have to move and find a new environment. And they all have to do this together, both infected and uninfected ants, and this helps overcome the period of self-isolation and performing tasks only near the place where they were introduced.”

“These results, as well as others not included in the paper, have allowed us to reach a point where we can very reliably introduce this pathogen into uninfected native supercolonies in the field,” LeBrun said.