ant-spore infection

Kathie Hodge kh11 at cornell.edu
Sat Sep 18 11:38:51 EST 1993


L. Detweiler wrote:
>Some time ago I saw a public television documentary on the rain forest.
It
>included information about a spore-ant relationship in which a fungal
spore
>infects the nervous system of ground-dwelling ants, causing them to go
>`insane' and begin climbing plants, where they die. The fungus then buds,
>grows, and releases new airborn spores from a high position.

Bizarre but true.  What you describe is typical of some insect pathogens
in the weird fungal order Entomophthorales (Zygomycota).  Insects doomed
by the fungus often climb up to high, exposed places and lock themselves
on by using their mouthparts in a deathgrip.  The fungus often further
secures them by sending out specialized hyphae that bind the unfortunate
bug to the substrate.  After they die, the fungus produces spores that
are forcibly discharged and thus escape into the air.

Although these fungi aren't too commonly found, you may be able to find
some RIGHT NOW if you go look on your windows for dead flies.  Look for a
dead fly hanging head downwards by its legs and proboscis, probably with
its wings held out to the sides, and surrounded by a delicate white halo
of discharged spores.  If you look closely, you'll see that the fly's
abdomen is swollen and between the segments you may be able to see white
masses of the fungus protruding.  This is most likely to be
_Entomophthora muscae_.

Although this climbing behavior is very typical of the Entomophthorales,
it can also be found in other fungi, such as species of _Cordyceps_ (a
very distantly related genus in the Ascomycota).  In fact, this may be
what your TV show was talking about, as the Entomophthorales are less
common in the tropics.  We know that these fungi do invade the brains of
their hosts, but we don't understand the mechanism by which they induce
this unusual behavior of climbing and locking on.  I wish we did. 
Perhaps someone out there in netland would find this an interesting
project!

My thanks to Ulf Andrick for his fascinating description of the biology
of Dicrocoelium dendriticum.

Kathie Hodge
kh11 at cornell.edu



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