Lab Core

Tobacco Hornworms


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Description of Research System

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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March 1999