Zombie Beetles Trick Others into Mating with Them

Goldenrod Soldier Beetles (credit)

Goldenrod soldier beetles infected with Empusa Lampyridarum, an entomopathogen, were first shown to exhibit peculiar behavioural and postural changes in 1888, but it was only recently discovered that some of these changes actually occur after the beetle is already dead.

 

Once infected with the fungus, the North American beetles climb to the top of flowers, which are usually used as a bed for feeding and mating, and firmly attach to them using their mandibles. They are then seen to assume a posture where their body is inclined upwards at a 45-degree angle, and their wings become raised as in flight.

Up until recently, it was assumed that the beetles adopted this position before dying, but a new study proves otherwise. The paper, written by scientists from the University of Arkansas and Cornell University, shows that this postural change doesn’t occur until well after the beetle is dead.

The fungus appears to kill the beetles after making them mount and hold onto the flower, and then controls the insect, making it appear zombie-like (i.e. like a revived corpse). The mechanism behind this change is not yet fully understood, but the authors of the paper suggest that the fungus grows inside the dead beetle. After 15-22 hours, the fungus is so big that it causes the meso- and metathoracic sclerites to become distorted. This could mimic muscle movements and cause the wings to open.

To make things even stranger, the position adopted by the zombie beetles is similar to their mating position. This is thought to be a way in which the fungus is spread between individuals. The male live uninfected beetles would proceed to mate with the corpses of the dead female beetles, which then allows the infection to spread.

Pathogens work in a way that will ensure their own survival, and spread to other hosts. The way they do this varies, and this particular fungus is thought to also spread through sporulation. This is when beetles infected with resting spores die, fall to the ground, causing the spores to be transmitted. These spores then germinate when conditions are favourable, and the disease is spread.

Further studies would need to be undertaken in order to study the exact mechanism of action of these different ways of transmission. It has been suggested to study the effect of gluing the infected beetles’ wings together, to see if this causes a decrease in disease spread.

Read the paper here: Steinkraus, D., Hajek, A., Liebherr, J. (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. http://www.sciencedirect.com/science/article/pii/S0022201117300824

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