Chemical attacks from parasites have big impacts on insects

Chemical attacks from parasites have big impacts on insects. A new study has revealed details about a behavior-modifying chemical warfare between leafcutter ants and the infectious parasites that live alongside them. The fungal parasite can overpower the leafcutter ants and control them, just as zombie ants are brainwashed to march out of their colonies by a different type of fungus.

Researchers from the University of East Anglia teamed up with experts at the John Innes Centre and other institutions to investigate colony collapse, when the highly efficient ant farmers suddenly abandon their carefully-managed gardens.

Leafcutter ants are common across Latin America and are the most highly-evolved of fungus-growing ants, adapting their farming skills around 60 million years ago. The larvae of leafcutter ants consume a specific specialized fungus, which the ants cultivate using a mulch of chewed leaves.

The farms of leafcutter ants are infected by a fungal parasite that has co-evolved to live off their fungal food supply called Escovopsis. The ants produce specialized bacteria on their bodies to control Escovopsis attacks, but the parasite can take over the fungus farm when colonies become stressed, resulting in colony collapse. Chemical attacks from parasites have big impacts on insects

“Leafcutter ants are superb farmers,” said study co-author Professor Matt Hutchings. “They patrol their gardens, remove foreign fungi and use antibiotic-producing bacteria on their bodies to kill off parasites – effectively using them as weedkillers. But the ways in which Escovopsis succeeds in getting through their defenses is not well understood.”

For the analysis, the researchers used samples of the food fungus from leafcutter ant colonies collected in Panama and infected them with the parasite.

The experts identified two families of molecules that were produced at high levels by the Escovopsis pathogen and tested them against the defensive bacteria produced by the ants.

The study revealed that the first molecule killed the ant’s bacteria, while the second manage to modify the behavior of the leafcutter ants. Under the influence of the second molecule, the ants fled their fungus garden. If the ants were exposed to the chemical weapon for long enough, it eventually killed them.

The strategy is similar to that used by a different fungus that is responsible for manipulating “zombie ants” to leave their colonies and climb up into the trees where they promote the spread of fungal spores after their death.

“We think the Escovopsis pathogen is always present in or around the nests and kept at bay by the ants’ constant gardening and chemical defences,” said study co-author Professor Barrie Wilkinson.

“But when something unusual happens – a drought, or other environmental change perhaps – the parasite may gain a foothold and start increasing the levels of the chemical weapon compounds that cause behaviour changes and decrease the ants’ weeding efficiency in their gardens.”

“From then on you have an escalating situation which leads to the appearance of dead ants, and the pathogen taking over, so the remaining ants eventually abandon the nest.”

Professor Wilkinson said that the research may lead to the development of ways to control pests such as leafcutter ants without using insecticides.

The research is published in the journal Nature Communications.

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By Chrissy Sexton, Earth.com Staff Writer

Image Credit: University of East Anglia