Please Do Now: What are
alkaloids, and what role do they
play in protecting the plant?
 Do
Now
 Evolutionary Arms Race notes
 Worksheet
 Nail the Quiz
 Gall Former Video

Plants defend
themselves from insect
pests with a wide
variety of tools
• Chemical
• Physical
• Indirect
When all your food is
protected in some way,
you have to find a way
around those protections
 Insect
herbivores and the plants they eat
are constantly adapting (though slowly)
new ways to get around defenses and
protect themselves
 We call this an “evolutionary arms race”
 Specialized
mouthparts for the
type of mechanical
defenses they will
face
 “window feeding” to
avoid the toughest to
eat areas
 Changes
in how their
stomach digests to
lessen the effect of
tannins
 Enzymes that
breakdown the toxins
that would harm them
(example, tobacco
hornworm and
nicotine)
 Often, plants
recognize the attack
of an herbivore from
its saliva
• To prevent
recognition, some
caterpillars can
produce chemicals
that “mask” their own
saliva
 Lots
of insects will
actually store the
chemicals that are
meant to kill them, to
protect themselves
from their predators
 Many
insects are
called specialists
because they only eat
one kind of plant
 This allows them to
be particularly
adapted to that
plant’s defenses
 Often
to prevent the
plant from signaling
there is an attack, or
from sending toxins
to the leaves, the first
bites will be to cut
the veins
• Called “trenching”
 Insects
are adapted
to feed on the leaves
that are least
protected, and at the
times of year when
they are least
protected
 Some
insects
manipulate the genes
of the plant to form
tumors, called galls,
that protect them and
provide them with
food
Monarchs only eat milkweed
 Milkweed is poisonous to
almost everything else
 The caterpillar actually uses the
toxins in the milkweed leaves
by storing them in its body,
making it poisonous itself
 Milkweed sends out chemical
signals to parasitic wasps when
it is attacked by monarchs, and
the wasps come and lay eggs in
the caterpillar that are
eventually fatal
