A tough question....

[David N. Gaines]

In article <4fvosk$20o at vixen.cso.uiuc.edu>, egrunden at prairienet.org 
says...
>
>
>
>Several years ago, I was watching a documentary about tropical 
rainforests.
>In this documentary they talked about a fungus that lives (for the most 
part)
>in the canopy. It drops its spores to the floor where they come in 
contact
>with a certain species of ant. They infect the ant and at a certain 
point in
>the ants life it is compelled (by the infection process) to climb a 
tree, and
>at the top it sinks its mandibles into a branch and dies there. The 
fungus 
>then sprouts from the dead body of the ant and the cycle continues.
>
>1) Does anyone know the name of this tropical fungus, or at least have 
heard
>   of it?
>
>2) How can a fungus influence a SPECIFIC behavior pattern to occur? I 
could
>   understand if the ant just went crazy and did random things, but how 
can
>   the exact behavior (climbing, clamping onto a branch,etc) be caused 
over 
>   and over?
>
>I realize this whole thing sounds a little hard to believe (I think so 
too)
>but that is what they said in the documentary. Anyone know of similar
>phenomena? 
>-- 
>                        *******************
>The Spirit of Nature, a powerful force,
>        belongs and returns to its creative source.
>- Excerpted from The Collective Works of Johnny Pokerface -

As an entomologist I study various wasps which are parasitoids of other 
insects (primarily moth and butterfly larvae).  I know of at least one 
species of Braconid parasitoid which passes it's larval stages inside the 
larvae of the imported cabbageworm (butterfly).  This parasitoid larva 
feeds on the inside of its host without damaging the host's locomotory 
musculature.  Fully developed (5th instar) larvae of the imported 
cabbageworm normally seek a concealed spot (away from predators and pupal 
parasites) in which to pass their pupal stage.  This behavior is seen in 
unparasitized cabbageworms only at the end of the fifth instar when 
pupation is imminent.  Parasitized larvae, however, seek a concealed spot 
in their fourth instar (pupation not imminent).  This allows the 
parasitoid larvae a quiet, concealed location in which to emerge from the 
host larvae and spin a cocoon.  The parasitoid cocoon is thus, less 
likely to be found by a predator or hyperparasitoid.  How is the host 
fooled into seeking a concealed location before it is fully developed?  
It sounds to me like hormonal control.

D. Gaines dgaines at vt,edu