"So, naturalists observe, a flea has smaller fleas that on him prey; and these have smaller still to bite ’em; and so proceed ad infinitum."
- Jonathan Swift

June 16, 2017

Eryniopsis lampyridarum

Mind-controlling fungi that manipulate ants have become quite well-know among the general public due to their ability to induce a "zombie-like" state in their host, but ants are not the only insects that can get infected by fungi, nor are they the only insects to get mind controlled by them. The study featured in this post is about a zombie beetle fungus call Eryniopsis lampyridarum which infects the goldenrod soldier beetle. Despite its name, the goldenrod soldier beetle is not as formidable as its name might indicate. The name is actually based on the first described soldier beetle species which has a colour pattern that resembles the coat of 17th-19th century British soldiers.

From Fig. 2 of the paper
The presence of E. lampyridarum in these beetles has been known for over a century, but relatively little research has been conducted on this pairing aside from some basic ecological research conducted in the 1970s and 1980s. It was not until now that someone has investigated this parasite-host interaction in close details, and provide descriptions of the fungal structure

From Fig. 4 & 5 of the paper
When the fungal infection in a beetle ripens, the infected insect will seek out a flower and clamp their mandibles around it in a vice-like grip. This is rather reminiscent of some zombie ant fungi which cause their hosts to position themselves on the underside of leaves where they can sprinkle spores into the path of uninfected ants. But the zombie beetles don't clamp themselves to leaves, nor do they bite down on just any old flowers, they only chose those from the Asteraceae - better known as daisies. After biting down on a daisy, the infected beetle succumbs to the infection. But the fungus is not done with its host quite yet.

Slowly, the dead beetle's wing covers and wings unfurl throughout the night, revealing a bloated abdomen brimming with fungal growth. By dawn the wings and their covers are full extended. So why have daisies as the final resting place for these zombie beetles? Also why unfold the wings and their covers at night just before daybreak?

For soldier beetles daisies, are like pubs or cafe - that's where they congregate to feed and possibly socialise with other beetles. So by placing itself on a flower, the zombie beetle is in prime position to meet its uninfected cousins. Unlike the zombie ant fungus which sprinkle its spores onto the ground to infect foraging worker ants, the spores of E. lampyridarum stays on the zombie beetle because that's where uninfected beetles are likely to come into contact with them.

With the fungal bodies sprouting from the abdomen, it seems that unfolding the wings would help expose the infective spores to potential host. However, there might be another reason for the wings to be unfolded. The researchers of this study suggested it actually serves the function of making the fungus-ridden corpse more attractive to uninfected beetles. Having the zombie beetle's wings open just before daybreak is also tailored to suit the daily routine of these beetles which are more likely to visit daisies in the morning. You can imagine that an unsuspecting goldenrod soldier beetle would visit a flower for a drink in the morning, meet some attractive looking beetles while it is there, only to end up with a fungal infection that will eventually take over them in body and mind

While some degree of mind-control is involved in getting the beetles to bite down on flowers, unfolding the wings seems to be a purely mechanical process. The wing unfolds long after the host has died, but the fungal growth propagate in such a way that it pushes the connective tissue at base of the beetle's wings and forces them to unfold. The fungus acts like the hand in a puppet, animating the beetle's dead body as if it is some kind of chitinous marionette.

But not all the infected beetles eventually become flower-clampers, some infected beetles simply die without ever climbing onto or clamping onto a daisy. In that case, the beetle are filled with thousands of resting spores, which unlike the ones on the zombie beetles, are not immediately infective. But those spores can last for a long time in the environment. For those beetles, when their bodies hit the ground and are broken apart by scavengers and microbes, they end up seeding the soil with a bank of viable spores.

So whereas the purpose of the infective spores on those flower-clamping zombie beetle is to spread the infection far and wide in the moment, those resting spores are an investment for the future - they are hardy and resistant, and their purpose is to wait in the soil for the next season, when they will unleash a brand new wave of zombifying plague.

Steinkraus, D. C., Hajek, A. E., & Liebherr, J. K. (2017). Zombie soldier beetles: Epizootics in the goldenrod soldier beetle, Chauliognathus pensylvanicus (Coleoptera: Cantharidae) caused by Eryniopsis lampyridarum (Entomophthoromycotina: Entomophthoraceae). Journal of Invertebrate Pathology 148: 51–59

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