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Description of Research
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Description of Tobacco Hornworm Research
System
Manduca sexta is a holometabolous, lepidopteran
insect. It has four distinct life stages: egg, larva, pupa
and adult. The larval stage may correctly be called a
caterpillar; it is commonly referred to as a tobacco
hornworm, although it is not a worm. The larvae normally
have five instars, although there may be six instars in rare
cases. The adult stage is the Carolina sphinx moth, also
called the hawkmoth. For more information about the life
cycle, including pictures, follow the link below.
Manduca sexta is an excellent model organism for
many reasons. First, the various lifestages of Manduca sexta
are available readily (see Organisms
and Supplies for more information). The insects are
commercially available as either eggs, early larval instars,
or pupae. In addition, rapid growth takes the organism from
eggs to pupae in just a few weeks. Field collection of M.
sexta (or a similar, species the tomato hornworm) often
can be performed during warm weather since the species are
pests of common garden tomatoes. Second, the facilities used
to rear the insects can be as basic as a benchtop with a 100
watt bulb or as sophisticated as a light, temp, and humidity
controlled incubator. Third, the insects have many easily
measured traits, including weight, length, rate of
development and feeding behavior. Fourth, a large quantity
of hemolymph (the circulating fluid in insects) can be
obtained from an individual, making physiological
experiments possible. Another advantage of M. sexta is that
it is being used to ask a wide variety of research
questions--from ecological and physiological to
cellular/molecular.
Manduca sexta is an important pest species on
tobacco, so the larval feeding habits are actively studied.
Topics under investigation include nicotine insensitivity,
palatability of food sources, taste reception, and
environmental effects on feeding behavior and growth.
The hemolymph proteins and their functions are another
area of active research. Proteins currently being
characterized include those involved in nutrient storage,
metabolism and transfer; wound healing and blood clotting;
hormone transport and metabolism; and immune responses.
Hemolymph is readily obtainable from the larval, pupal, and
adult stages. A variety of available assays make comparative
analysis at either a quantitative or qualitative level
feasible in undergraduate laboratories.
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