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Tobacco hornworm (Maduca sexta)

    Also called the tomato hornworm.  In nature, the large tobacco hornworm moth first emerges in early summer.  The pupal case splits and the moth struggles out.  The moth crawls about, usually finding a surface that it can climb and cling to.  If it cannot find a vertical surface, the wings will crumple as they unfold and the moth will be unable to fly.
    The female hornworm moth with mature eggs produces a sex pheromone which attracts males.  Primarily, only the unmated female produces the pheromone so mating of the female occurs only once, although a male may mate with several females.  Mating usually occurs during the night on a vertical surface.  With the female uppermost, the pair face in opposite directions with their abdominal tips touching.  Mating often lasts for several hours.
     The female moth usually begins depositing eggs on the third night after emerging from the pupal case.  Eggs are deposited singly on the underside of leaves.  The smooth, pale green egg is about 1 mm in diameter and almost spherical.  The color fades, becoming almost white before hatching which requires three to eight days depending mainly on temperature.
    The larva eats the leaves of a wide range of solanaceous plants (tomato, tobacco).  It passes through five, occasionally six, larval instars (stages between molts) before the pupal instar.  Most larval growth occurs in the fourth and fifth larval instars, especially the fifth.
    Upon maturation of the larva, the dorsal aorta or heart becomes visible along the dorsal midline.  This dark pulsating line is first visible just anterior to the horn.  At this time the larva stops eating, leaves the host plant, and tunnels into the soil.  There it forms a chamber or cell in which to pupate.  Before the actual larval-to-pupal molt, the larva enters a stage called the prepupa.  It becomes inactive, shrinks in size, and its color fades somewhat.  On about the sixth day after entering the ground, pupation occurs. 
    At first the pupal cuticle is transparent, revealing the bright green of the inner tissues.  At this time the pupa is soft and easily damaged.  Gradually the cuticle aquires a reddish-brown color, becomes opaque and hardens.  Within the pupal case all appendages are tightly fused to the body, with the exception of the tongue.  Free along most of its length, the tongue bows out in its own case.  The only movable part of the body is the abdomen.  In nature, pupae formed in early or mid-summer emerge within a few weeks, but pupae formed in late summer emerge the following spring. 

Availability: Tobacco hornworms are available now. After you have a cage and supplies ready, contact Liz (eegraham@life.uiuc.edu) to schedule a pickup time (right after class is convenient). We will send you a tobacco hornworm  in a plastic container, and some diet medium to get you started.

Housing: It is possible to carry the tobacco hornworm through its complete life cycle in 30 days.  The critical factors are light and temperature.  The larva must receive constant light, otherwise the pupal stage may be extended for several months (diapause).  A temperature of about 80 degrees F should be maintained throughout the larval stages.  Lower temperatures can prolong the life cycle, while temperatures over 90 degrees F can kill the organism.
    The young larvae are easily damaged by handling, therefore, it is best to use a paintbrush to move them when they are smaller than 1 inch long.  Put each larva into each vial of medium you will receive (do not put more than one larva in each vial).  Lay the vials on their sides and place a lamp with a 100-watt bulb about 10 inches above them.  The light must remain on constantly throughout the larval stages.  Temperature can be regulated by moving the lamp toward or away from the vials.  Check the temperature at least twice a day to make sure it is at 80 degrees F.
   The larva should be ready to pupate four to eight days after arriving.  Every day examine each larva for the appearance of a dark, pulsating line (aorta) along the dorsal surface.  This line usually first appears just anterior to the horn.  When the line first becomes visible, prepare the larva for pupation. Delay at this point often results in the death of the larva.
    Remove the larva from its vial and wash any remaining culture medium from the vial with a jet of water (do not use soap or detergent).  Replace the larva and cover it with a dry inert material (e.g., shredded paper, sawdust, potting soil) until the vial is about half full, then recap.  Do not overfill or pack the vial; the larva needs space in which to pupate.  The larva also needs darkness, so wrap the vial in newspaper and secure with rubber bands.  Continue to maintain the larva at 80 degrees F, if necessary, use a lamp.
    It is possible to follow the transformation of larvae to pupae by uncovering the vials for brief periods each day.  However, do not remove transforming larvae from their vials.  Pupation should be complete in seven days, and the pupae can then be removed and examined if desired.  Be careful when handling the pupae as they are easily damaged.  No later than 14 days after the larvae have been prepared to pupate, the pupae should be readied for adult emergence. 
    In preparation for the emergence of the moth, pupae should be transferred to a cage or other container (e.g., a terrarium).  While in the cage they should be maintained at room temperature amd exposed to a normal day-night cycle.  The cage must contain a vertical surface (cardboard, newspaper) that the moths can climb and cling to, or their wings will crumpleas they unfold and the moths will be unable to fly.

Food: You will receive culture medium to feed the larvae on.  If mold appears in the culture medium, remove the larva, wipe excess moisture from the vial, and replace the larva.  Removing the mold with point of a knife may also help.  Larvae can be fed on live tomato plants, if untreated (pesticide, insecticide-free) plants are available to you.  Adults can be fed a solution of sugar water.