University of
Nebraska		 Ent logo Department
of Entomology





Manduca sexta Tobacco Hornworm
Photograph from Dr. Richard Vogt's page: http://zebra.biol.sc.edu/moth/manduca-l.html
 


Classification

Kingdom: Animalia

Phylum: Arthropoda

Class: Insecta

Order: Lepidoptera

Family: Sphingidae

Genus: Manduca


Species: Manduca sexta



Introduction

Manduca sexta, referred to as the tobacco hornworm (caterpillar) or as the hawkmoth or sphinx moth (adult), is a common insect in a wide variety of habitats, such as tobacco fields and vegetable gardens.

They are called hornworms because, as many caterpillars in the Sphingidae family, they have a conspicuous horn or spine on the top of the last abdominal segment.

5th instar larva


Metamorphosis: Complete

Egg, larva, pupa, adult

Hornworm eggs are deposited mainly on the lower surface of foliage, but can also be found on the upper surface.



Larvae are cylindrical and bear five pairs of prolegs in addition to the thoracic legs. As mentioned before, the most striking feature is the "horn" located on the terminal abdominal segment.

The University of Arizona - 2001 The Manduca Project


There are usually five instars. The first instar larvae have very long horns compared to the fifth instar.

First instar Second instar Third instar
Fourth instar Fifth instar



Hornworms primarily feed on tobacco and tomato, butwill occasionally feed on potato and pepper crops and other plants in the Solenaceae family, hence their name Manduca, which is the Latin word for "glutton". One or two hornworms can easily defoliate a tomato plant.
Mature larvae drop to the soil and burrow, where they pupate. Pupae are brown in color, large and elongate.

The University of Arizona - 2001 The Manduca Project



Adults are large moths with long forewings. Their abdomen is marked with orange-yellow spots. They are strong fliers with a rapid wing beat and are sometimes mistaken for humming birds. Adults are generalist nectar feeders.

By John Himmelman




Distribution

The tobacco hornworm is more common in the southern United States, especially the Gulf Coast states. Its range extends northward to New York. It also ranges south through Mexico and the West Indies to Argentina.

Importance

Larvae are defoliators and can be considered pests in gardens and a menace to tobacco growers due to the high levels of defoliation.
Hornworms are an appealing system to researchers because they are easily reared in the laboratory on artificial diets, have a short life cycle, and their large size allows for scientific investigations on their various systems. Current research on Manduca sexta includes:

  • Flight mechanisms in the moth
  • Larval nicotine resistance
  • Hormonal regulation of development
  • Hemolymph physiology
    •



    Molting Process:

    Terminology:

  • Molting: the shedding of the old cuticle and production of a new one
  • Ecdysis: component of the molting process, shedding of the cuticle
  • Instar: stage of insect between molts

    • egg - molt - 1st instar - molt - 2nd instar - molt - 3rd instar - molt - 4th instar - molt - 5th instar

    Process:

    Molting is a complex process under hormonal control. Hormones are chemical substances produced by the endocrine system that affect target organs within the insect. There are basically two molting commands regulated by various hormones:

    Commands:

  • Time to molt - controlled by the brain hormone and ecdysone
  • What to molt into - controlled by juvenile hormone


    • Time to molt:

     

    Endocrine Tissue
    responsible for secreting:

    		 Hormone: Function:
    Protocerebrum Brain Hormone or PTTH Activates Prothoracic gland
    Prothoracic gland Ecdysone Initiates the molting process



    What to molt into:

     

    Endocrine Tissue
    responsible for secreting:

    		 Hormone: Function:
    Corpora Allata Juvenile Hormone It's quantity determines what
    to molt into


    Possible outcomes:

  • High level of juvenile hormone + ecdysone = molt into larval form (retains same form)
  • Reduced level of juvenile hormone + ecdysone = molt into new form (example: pupal stage)
  • No juvenile hormone + ecdysone = molt into new form (example: adult form)




    • Interesting Facts

    Tobacco plants and other Solenaceous crops are rich in alkaloids. The most studied alkaloid is nicotine in the tobacco plant. The nicotine in the tobacco plant leaf is toxic to most insects, however, the Tobacco hornworm is able to succefully feed on this plant. Hornworms have a special mechanism for selectively sequestring and secreting the nicotine, so ,basically, it is not toxic to them.



    Frequently Asked Questions:

    Your hornworm "old cuticle" is "stuck". If this happens, you should remove the skin so that it does not constrict the hornworm's body. The best way to do this is with a small scissors.

    No, your hornworm is not dead! It is going to pupate (it is a pre-pupa).

    Links

    University of Florida - tobacco hornworm:

    http://entnemdept.ifas.ufl.edu/creatures/field/hornworm.htm


    Manduca sexta sexta by Bill Oehlkew:

    http://www.silkmoths.bizland.com/msextsex.htm



    Northern Prairie Wildlife Research Center - Carolina Sphinx:

    http://www.npwrc.usgs.gov/resource/distr/lepid/moths/az/1081.htm


    Ecdysis - IAC-USNC:

    http://www.iac-usnc.org/Methods/moth/ecdysis.html


    University of Florida:

    http://edis.ifas.ufl.edu/BODY_IN158


    Hornworms - NCSU:

    http://ipm.ncsu.edu/AG271/tobacco/hornworms.html


    The Manduca Project - The University of Arizona:

    http://insected.arizona.edu/manduca/