Life cycle of an ant-infected fungus, Ophiocordyceps unilateralis

Ophiocordyceps unilateralis infects ants, modifies their behavior, and is found in many countries around the world. One unifying concept of all such parasitic associations is that both the parasite and the host adapt to maximize their fitness and reproductive output. In the case of O. unilateralis, infected ants develop erratic behaviors that include leaving their nests, climbing trees and hanging themselves from leaves by their jaws to disperse fungal spores.

In an attempt to understand the life cycle ofthis pathogen,BIOTEC research team surveyed a permanent plot in Khao Yai National Park and recorded the presence of dead ants infected by this fungus. Each dead ant was followed, and new dead ants were recorded monthly over the course of two years. It was found that out of thirty seven species of live ants found on site, only 10 species of ants in the genera Camponotus and Polyrhachis were infected with O. unilateralis/H. formicarum. Researchers were able to describe the life cycle of O. unilateralis as consisting of three distinct stages: 1) dead ants (DA) infected by the fungus are typically found on the underside of leaves in tropical rainforests; 2) a fungal stroma (S) then grows from the back of the head of the dead ants; and 3) a perithecia pad (P) develops from the fungal stroma for spore dispersion. Researchers also reported that O. unilateralis occurrence on ants has a seasonal pattern with peaks in both the rainy and dry seasons.

Understanding the life cycle of this pathogen and its temporal pattern of infection could have important impacts on the ant population and will provide a foundation for further study of the host-parasite association.


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The result of this study was fully reported in an article titled “Life cycle, host range and temporal variation of Ophiocordyceps unilateralis/Hirsutella formicarum on Formicine ants” in the Journal of Invertebrate Pathology. The article was also featured on A-IMBN Research.

Posted on 25 December 2012