So another question we have just recently been dealing with
is, do predators and parasites of herbivores
influence their feeding habits and host plant choices?
And let me just tell you about Carcelia.
The main enemy of Estigmene in Southern Arizona
is a fly called Carcelia.
And just like with the Manduca I told you about,
this thing lays eggs on the surface of the caterpillar.
And when the maggot comes out, it bores through the cuticle
and eats out the inside of the caterpillar and kills it.
And so it's a pretty nasty piece of work.
[LAUGHTER]
And actually, these flies are really common.
And this whole family of flies is really common.
When you're out having a picnic and you think, ooh,
nasty flies, they're probably doing a really good job
killing caterpillars.
And this is what happens to the caterpillar.
It's totally eaten out by the maggots.
And the maggots come out and make their own pupae.
And these will become new flies to infect
a new lot of caterpillars.
Well, what we found was that the parasitized caterpillars
show an increased responsiveness to PA
and decreased responsiveness to bitter.
So we tested the sugar cell.
No change in the unparasitized and the parasitized.
Do you mean these are caterpillars in the process
of being eaten out from the inside?
Yes.
So we collected a load of caterpillars
from the field, tested their sugar cell, their PA
cell, and the cell's response to bitter compounds.
And then we dissected them and see
which ones had maggots in them.
So the sugar cell wasn't altered by the presence of maggots
inside.
Nope-- no effect.
But the PA cell, if they had maggots inside,
they were much more sensitive to PAs.
And the PAs is a plus cell, remember.
It's going to make them eat if they contact the PAs.
And the presence of maggots here reduced the sensitivity
to the bitter compounds, to the deterrent compounds.
Now, the PA plants have PAs of course.
They've also got deterrents.
So what this means is that they'll eat more PA plants
if they've got parasites.
And that means they'll destroy more parasites within.
So it's a little bit of a complicated situation.
But the presence of the parasites
makes them behave in a way that's really adaptive.
I have a question.
Yeah?
Once the parasites get in, is that it?
Is it all over?
No.
Or can they chase them out?
Yeah, if they eat enough PAs, they
can kill a lot of those parasites.
And then they can often survive.
So in fact, what we're talking about
here is that the parasites do indeed make them eat more PAs
and tolerate strange, bitter chemicals.
And this helps them get rid of the parasites.
And so even caterpillars can self-medicate.
[LAUGHTER]
I love all this neurophysiology stuff.
Because actually, what's amazing with insects
is what the taste cells respond to is determining
a lot of the behavior.
And with ourselves and a lot of vertebrates,
there's a more complicated issue with the brain and experience,
not to say these things don't learn.
But the fact that their taste cells
can change with what they need is just
something kind of different.
Are their taste cells responding to some chemical
released by the parasite?
We don't know the precise feedback mechanism
at this point.
That's one of the issues we need to know.
And so, anyway, I love all these spikes.
And these are called spike trains.
And these are a load of spike trains
over half-a-second interval.
It looks like the broadside.
Yeah.
This is right.
So here we are.
"Precision."
"Spike trains thread through a Siberia of nerve cells.
Messages synapse.
Whispers of sodium and potassium engage
in organization memories.
Voices vie for attention.
Serotonin, tryptamine, octopamine open doors
or close them, change receiver cells,
vary values of electric language.
The spike trains of nerves, interplay of inconstancies,
yet without indecision.
Stranger than fiction."
And I have some woolly bears for you.
This is Grammia.
It's not the one that I've been talking--
it's not this.
But it's a related one.
And in that box of insects, you had some specimens of Grammia.
And these are caterpillars of Grammia
that I collected a week or so back
in the Patagonia mountains.
Again, they're feeding on synthetic diet.
You're welcome to pick them up.
They're really cute.
They're not bad for you at all.
They're surprisingly good at escaping, however.
So if you pick them up, I suggest you do it over the dish
so that when they get out of your control, they go back in.
So that's really the end of what I want to tell you about.
And I'll leave you to play with Grammia.
[APPLAUSE]