Fungi that influence INSECT behavior.

Paul Zambino paulz at PUCCINI.CRL.UMN.EDU
Fri Jan 31 09:58:06 EST 1997


>Eric Grunden Wrote:
>
>I saw a documentary a few years back that talked about a
>tropical upper canopy fungus. It dropped its spores, some
>of which landed on ants. Unexplainably, and for no apparant
>reason, after a couple of weeks the ground-dwelling "infected"
>ants climb to the top of a nearby tree, sink their mandibles
>into a branch and then die. Then the fungus sprouts from
>the dead ant and the process begins again.
>
>My question is;  how can a fungus trigger the specific
>behavior of climbing the tree and sinking the mandibles in?
>I could understand if it had different effects on each
>ant (e.g. "insanity", spasms, etc.), but I do not understand
>how it can cause specific actions to be carried out.
>Any hyptheses?................
>
>Anyone heard of this fungus or remember the documentary?
>
>--------------------------------------------------------------------------
>--------------------
>
>Jim Responds:
>
>Yes!  I remember this documentry.  There is a scientist who works with
>ants who has written many books on the subject for all readers.  He
>isolated the compound that signals ants that another ant is dead. When he
>put a drop on a live ant, other ants would carry him out of the nest and
>through him into the dead ant pile.  Despite the ants protests ("I'm not
>dead yet!"), and his wiggling arms and legs, his nest mates refused to
>reasses his condition.
>    Ants are highly dependent on very simple chemical signals, and so were
>a natural victim for this isidious fungus.  However, I too am amazed by
>this process.  For natural selection to arrive at this is truly a miracle.
> The fungus that made ants climb high must have survived better than those
>that did not.  And, of these fungi the one that contained the "bite down
>and die" chemical must have done even better.
>     While there are some fungi that can change human behavior, the
>results are less predictable.  I like to think that if I eat mushrooms and
>climb a tree it is by my own free will, but who knows?
>
>
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>------------------------
>
>"Those who have nothing to say usually say it about spelling."
>-Jim Berlstein, BFD

The triggers for climbing and biting could be chemical, but are probably
due to changes in the internal physiology of the ant triggering natural
responses.  The climbing response could be due to the fungus interfering
with respiration.  Natural conditions where an insect would be oxygen
starved would be if they are wet.  Insects may believe they are climbing to
get out of water, the same way that people seek open air when they feel
that they are suffocating.  For the clamping down, there might be other
mechanisms that do not require a specific chemical signal.  For example,
animals stretch and yawn when we are tired or have sore muscles.  Ants
might bite when they are infected because they have unusual sensations in
their muscles.  Alternatively, they may have a general tendency to bite
when they perceive threat. In this case the threat would be sensations from
their own internal disease.  Once clamped, they may have no mechanism for
releasing their mandibles as they die.  As an illustration, some native
tribes use ants with large mandibles as sutures to close wounds, getting
the ant to bite on the appropriate spot, and then severing the head.  The
"clamping" muscles, are probably stronger than "releasing" muscles.

The "fly fungus" Entomophthora muscae causes some similar behavior in
flies.  Infected flies, climb  a pane of glass or to the tip of a blade of
grass, extend their proboscis, and then are unable to let go.  In this
latter case, there may be a chemical change in the flies saliva, as there
is no mechanical reason why the probosis should stick.  Does anyone know if
the chemical that causes the stickiness is present in normal flies but at
lower amounts, or is it produced by the fungus?  I know that the
Entomophthora spores are themselves quite sticky.  Paul

Paul Zambino, Ph.D.
USDA Forest Service
Forestry Sciences Lab
5985 Highway K
Rhinelander, WI 54501
PH:(715)362-1178
FAX: (715)362-1166
EMAIL: paulz at puccini.crl.umn.edu
DG:p.zambino:R09F06A





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