Natures wonders: fungus controls of insects (Introduction)

by David Turell , Friday, February 24, 2023, 19:51 (425 days ago) @ David Turell

A new review of fungal controls of insects:

https://www.quantamagazine.org/can-a-fungus-really-take-over-our-brains-20230223/

"In these zombie-like cases, the pathogen (whether it’s a virus, bacteria or fungus, or something else) acts specifically to change the behavior of its host.

"While we know a decent amount about these pathogens — including the very real Ophiocordyceps fungus, which does turn insects into unwitting agents of societal collapse — there’s still much to learn.

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“Cordyceps” has become a common catch-all name for a group of fungi that infect insects. This grouping includes the species Ophiocordyceps unilateralis, better known as the “zombie ant fungus.” It spreads by sprouting fungal structures that erupt through the ant’s head after its death.

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"...the fungus induces an infected ant to leave the nest, climb above it, and bite into nearby vegetation as it is dying — a practice known as summiting. A day or two after the ant’s death, the parasitic fungal spores erupt out of the ant’s head to shower the colony with the pathogen.

"Ophiocordyceps-infected ants aren’t the only ones who exhibit this climbing behavior upon infection. It is widespread across different categories of insects and can be caused by viruses, single-celled parasites called trematodes, and various species of fungi unrelated to Ophiocordyceps. It even has a common name: summit disease.

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"We don’t know for sure. Recent studies have found chemical signals from the fungi in infected insects. Some of these signals — likely secreted proteins — may target the host’s behavioral systems and control behavior like summiting and nest desertion.

"Scientists hypothesize that pathogens may be taking advantage of preexisting behaviors governing molting and sleep, which evolved millions of years ago. Molting — the process by which an insect sheds its protective exoskeleton to grow a new, bigger one — is a time of vulnerability, since it takes a day or two for the new exoskeleton to harden enough to provide safety. Insects have evolved behaviors for this time that can include wandering from the nest and summiting. Sleep is also a vulnerable time, so some insect species have learned to sleep while grasping onto grass or leaves.

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"Molting and sleep are controlled by the insect’s circadian rhythm, and summiting appears to be as well, as many species of infected insects do this at predictable times. In Ophiocordyceps-infected carpenter ants, for example, summiting always happens around solar noon. The biological machinery associated with an insect’s circadian rhythm therefore seems like a good place to explore."

Comment: remember we saw leaf-cutter ants described here years ago. Based on this article, the field has not advanced as much as could be hoped.