Tobacco Hornworm Facts

Tobacco hornworm is one of the most common insects in the garden. They are scientifically known as Manduca sexta and belong to the Sphingidae family. They are the larvae of the Sphinx moth and are often confused with the tomato hornworm or Manduca quinquemaculata that belongs to the same genus but as is clear from the scientific name, is a distinct species. In order to understand the insect better, let us consider some tobacco hornworm facts in this article.


Habitat and Distribution

Tobacco hornworms are very common in the southern states of the United States although their habitat stretches from Canada to Argentina. The tobacco hornworm habitat include the foliage of plants belonging to the Solanaceae family. Their most favorite host is the tobacco plant. In nature, tobacco hornworm diet includes leaves of the plants that they grow on. When raised in laboratory for scientific studies, the tobacco hornworm diet is wheat-germ based.

Life Cycle

Tobacco hornworm life cycle is a short one that spans over 30 to 50 days. It begins with the eggs that hatch into larvae. The larvae become the tobacco hornworm pupa that finally matures into an adult. The emergence of an adult moth by the transformation of the larva is an example of complete metamorphosis. Here is a step by step account of the tobacco hornworm life cycle.

Eggs
Tobacco hornworm eggs are spherical and translucent green in color. They are mostly found on the lower surface of leaves. However, occasionally these may also be laid by the female moth on the upper surfaces of leaves.

Larva
Within 2 to 4 days after they have been laid, the tobacco hornworm eggs hatch into larvae. Also known as the tobacco hornworm caterpillars, these larvae are green in color and about 70 millimeter in length. They feed on the foliage of the plant on which the eggs were laid. The tobacco hornworm caterpillar goes though 5 larval instars or developmental stages that span over a period of about 20 days. Throughout the successive instars, the caterpillar grows in size. The characteristic horn or spike on its abdominal segment that gives the caterpillar its name also keeps reducing in length in each successive instar. As the caterpillar approaches the final stage, it starts looking for a place to burrow so that it can enter its next stage, which is the pupa stage. This behavior of the pupa is rightly termed as wandering.

Pupa
Once the tobacco hornworm larvae mature, they drop on the ground and burrow into the soil to a depth of 10 to 15 cm. Here, they form a brown or reddish-brown colored pupa which is elongated and oval with a pointed posterior end. The tobacco hornworm pupa has a pronounced maxillary loop that encase its mouth parts. This loop extends to almost one-fourth the body length of the tobacco hornworm pupa. However, in case of the tomato hornworm pupa, the case is one-third the length of the pupa. The pupal stage is long and its duration is variable.

The Adult
The adult form of the tobacco hornworms are known as Carolina Sphinx moths or hawk moths. They are sexually dimorphic and have large forewings. Their identification marks are the orange yellow spots on their abdomen. The adults feed on nectar of flowers. It is due to their powerful and rapid beating of the wings that these moths are also known as the hummingbird moths. These moths are seen hovering over flowers during dusk.

• Tobacco hornworm is a model organism and is commonly used in neurobiology due to its short life cycle and easily accessible nervous system.
• The tobacco hornworm caterpillar causes great damage to the leaves of a tobacco plant. Just two such caterpillars can defoliate an entire plant.
• The distinguishing feature between tobacco hornworm and tomato hornworm caterpillars are the markings present on their bodies. While the tobacco hornworm has white diagonal lines, the tomato hornworm has V-shaped markings on its body.
• Tobacco hornworm caterpillars can be controlled using insecticides.
• Natural enemies include the stilt bug Jalysus spinosus that attack hornworm eggs. The braconid wasp is a tobacco hornworm predator that lays eggs in the hornworm. As the eggs hatch, they eat their way out of the caterpillar slowly killing it.

One of the alarming tobacco hornworm facts is that due to their voracious appetite, these insects are one of the most destructive pests of the tobacco plant . If their growth is left unchecked, then tobacco hornworms are capable of destroying an entire crop.