|
Research System Home
Page
Research Based
Labs
CO2
herbivory
|
|
The Effect of Elevated CO2 on Tobacco
Hornworm Herbivory
--Overview--
One of the most interesting responses to carbon dioxide
increase that biologists have observed is a change in the
way insect herbivores feed. A number of studies have shown
that the rate of feeding increases in an atmosphere
with more carbon dioxide than at present. This is not caused
by a direct impact on the insects; they seem to have no
response to widely varying amounts of carbon dioxide.
Rather, plants grown in an atmosphere with more carbon
dioxide seem to change in their chemical makeup, and the
insects change their feeding behavior in response to the
different plant composition.
Changes in herbivore feeding have been studied in few
species to date, and there has been no work on Manduca
sexta larvae yet (to our knowledge). You will feed your
M. sexta larvae leaves from their usual food source,
tobacco (Nicotiana tabacum). Some of the tobacco
plants will be from the growth chamber with a control
atmosphere and some will be from the chamber with extra
carbon dioxide added. The data of interest are the rate
of leaf consumption by the larvae (area of leaf eaten
per hour) and rate of larval growth on the two types
of leaf.
Each pair of students should pick two larvae that are as
similar as possible in size. Before you start this process,
work through the timing so that you (or your partner) can be
sure to be available for each step. The best plan is
probably to start the experiment in the evening between 8
and 11 PM; the 12 hour intervals will then occur in the
evening and in the morning.
- Start time. Choose your two larvae and
put them into two separate clean containers. Flip a coin
to decide which type of tobacco leaf each larva will feed
on and label the container. Leave them in these empty
containers for 12 hours in order to clear their guts of
food.
- 12 hours after start. Weigh the larvae
individually and return them to their containers. Select
a whole tobacco leaf from a plant grown in high carbon
dioxide and from a plant grown in a control atmosphere.
Try to make the two leaves as similar as possible in size
and appearance. Determine the area
of the leaf. Tear the leaves in one or two places
(careful not to break any pieces off) to give the larvae
a good place to start feeding. Put one leaf in each of
the containers with the now-ravenous larvae. Wait 12
hours.
- 24 hours after start. Remove what's
left of the leaves from the containers, and determine the
area once again. If the leaf is in pieces, be sure to
measure the area for all of them. Return the larvae to
the empty containers, and wait 12 hours to clear their
guts once more.
- 36 hours after start. Weigh the larvae
again, then return them to their luxurious chambers with
unlimited food. Calculate growth rate as weight gained
per unit weight at the beginning of the experiment.
Protocols:
Measuring leaf area.
|
