Manduca sexta facts for kids
Quick facts for kids Manduca sexta |
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The Manduca sexta is a type of moth found across North and South America. It was first described by Carl Linnaeus in 1763.
This moth is often called the Carolina sphinx moth or tobacco hawk moth when it's an adult. Its caterpillar form is known as the tobacco hornworm or goliath worm. It looks a lot like the tomato hornworm (Manduca quinquemaculata). Both caterpillars eat the leaves of plants in the Solanaceae family, like tobacco and tomatoes.
You can tell the two hornworms apart by their side markings. Tobacco hornworms have seven white diagonal lines with black borders. Tomato hornworms have eight V-shaped white markings without borders. Also, tobacco hornworms have red "horns," while tomato hornworms have dark blue or black ones. A trick to remember is that tobacco hornworms have straight lines, like cigarettes. Tomato hornworms have V-shapes, like "vine-ripened" tomatoes.
The tobacco hornworm can handle nicotine from tobacco plants. It can even use this nicotine to protect itself from predators. Scientists often study M. sexta because it's a great model organism. Its nervous system is easy to access, and it has a short life cycle. This makes it useful for many science experiments, especially in neurobiology. It's also easy to raise in a lab.
Contents
Life Cycle of the Tobacco Hornworm
The Manduca sexta has a quick life cycle, usually lasting about 30 to 50 days. In most places, there are two generations of these moths each year. In warmer areas like Florida, there can be three or four generations.
Eggs: The Start of Life
M. sexta eggs are round and about 1.5 millimeters wide. They are a clear green color. These eggs usually hatch within two to four days after being laid. Moths typically lay their eggs on the underside of plant leaves, but sometimes they are found on the top.
Larva: The Hungry Caterpillar
M. sexta larvae are green caterpillars that can grow up to 70 millimeters long. If they are raised in a lab and fed a special diet, they might look turquoise. This is because their blood, called hemolymph, is blue. When they eat plants, they get yellow pigments called carotenoids. The blue and yellow mix to make them green.
Tobacco hornworm caterpillars love to eat plants from the Solanaceae family. Their favorite foods include tobacco, tomatoes, and Datura plants. The caterpillar goes through five growth stages, called instars. After each instar, it sheds its skin in a process called molting. If they don't get enough food, they might have extra instars.
When the caterpillar is almost ready to change, it starts to "wander." It looks for a good spot underground to turn into a pupa. You can tell it's ready because its heart, a long pulsing vessel on its back, becomes visible through its skin.
Sometimes, tiny braconid wasps called Cotesia congregata lay their eggs inside hornworms. The wasp larvae grow inside the caterpillar. Then, they come out and spin small, white cocoons on the hornworm's body. People sometimes think these are the hornworm's eggs. Another wasp species, Polistes erythrocephalus, also eats hornworm larvae.
Pre-pupa: Getting Ready to Change
Before the caterpillar becomes a pupa, it goes through a "pre-pupa" stage. During this time, it shrinks a lot and gets ready for its big change. People sometimes think the caterpillar is sick or dying during this stage.
Pupa: The Resting Stage
The pupa stage lasts about 18 days in a lab. If the pupae are kept in short daylight (12 hours light, 12 hours dark), they can enter a resting state called diapause. This can last for several months. During this stage, the moth's adult body parts form inside the pupal case. When the adult moth is ready, it breaks out of this case.
Adult: The Flying Moth
Adult M. sexta moths have narrow wings that can spread about 100 millimeters wide. They drink nectar from flowers. These moths are amazing at hovering in the air while they feed.
Male and female moths look a bit different. Males have wider antennae and special claspers at the end of their bodies. Female moths are usually ready to mate about a week after they emerge. They typically mate only once, while males can mate many times. Mating usually happens at night on a vertical surface and can last for hours. After mating, females lay their fertilized eggs on plant leaves, usually on the underside.
Raising Them in a Lab
Like the fruit fly Drosophila melanogaster, M. sexta is often used as a model organism in science. They are studied a lot because they are big and easy to raise. They can be fed host plants like tobacco or a special artificial diet. It's important to give them a "long day" (about 14 hours of light) to stop them from going into diapause.
To start, eggs are rinsed in a weak bleach solution to clean them. Then, the eggs are placed on food or plants. The caterpillars grow at different speeds depending on the temperature. As they eat, they are moved to fresh food. When they start to "wander," they are placed in a special chamber to turn into pupae. After they become pupae, they are moved to a breeding area. If you give them sugar water and a tobacco plant, the female moths will lay fertile eggs, and the cycle can start again.
If hornworms eat an artificial diet, they might not get enough yellow pigment called xanthophyll. This can make them look blue instead of green. Also, if their diet lacks carotenoids, which are needed for good vision, they might not see very well.
As Pet Food
Hornworms raised in labs are often fed to exotic pets that eat insects. These include some reptiles, fish, and small mammals. Lab-raised hornworms are safer than wild ones because wild hornworms might have eaten poisonous plants. Hornworms are now farmed specifically for pet food. They are often sold in containers with all the food the larvae need. They are easy to care for, and pets seem to love their bright color and taste.
Subspecies of Manduca sexta
- Manduca sexta caestri (Blanchard, 1854) (found in Chile)
- Manduca sexta jamaicensis (Butler, 1875) (found in the Caribbean)
- Manduca sexta leucoptera (Rothschild & Jordan, 1903) (found in the Galápagos Islands)
- Manduca sexta paphus (Cramer, 1779) (found in South America)
- Manduca sexta saliensis (Kernbach, 1964) (found in Argentina)
- Manduca sexta garapa (Pixley, 2016) (found in Saipan)
- Manduca sexta sexta (found across the Americas)
Behavior of the Tobacco Hornworm
How They Eat
Tobacco hornworms are flexible eaters. The caterpillars can grow on many different host plants. However, they prefer plants in the Solanaceae family, like tobacco and tomato plants. They grow faster on these plants. Special sensory parts on their mouths help them find these plants. They recognize a chemical called indioside D found in these plants. Tobacco hornworms are seen as pests because they eat the top leaves of tobacco plants and leave droppings. Adult moths do not harm plants because they only drink nectar.
Tobacco hornworm larvae like places that are humid. If they get thirsty, they will move towards water or a very humid area. They use their antennae to find water to drink.
How They Defend Themselves
Nicotine is usually poisonous to most animals because it affects their muscles. But the tobacco hornworm can process nicotine from tobacco plants. It then uses this nicotine to defend itself from predators. It has a special gene that changes nicotine into another substance. Some of this changed nicotine is sent to its blood and then turned back into nicotine. The hornworm then releases this nicotine into the air from its breathing holes. This is like "toxic bad breath" and helps scare away spiders. Studies have shown that hornworms that ate plants with less nicotine were more easily caught by wolf spiders.
When tobacco hornworm caterpillars are attacked, they make short clicking sounds with their mouthparts. Scientists think these clicks are a warning sound to predators. It tells them that trying to eat the caterpillar will be difficult. After making these sounds, hornworms have been seen thrashing and biting their attackers. These clicks can be heard up close and have a high frequency. The more they are attacked, the louder and more frequent the clicks become.
Gallery
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An old drawing from British Entomology
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A tobacco hornworm eating a tomato plant
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A tobacco hornworm with tiny wasp larvae on it
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A tobacco hornworm covered with white wasp cocoons
Images for kids
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With parasitic wasp cocoons
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Manduca sexta parasitized by braconidae wasp larvae
See also
In Spanish: Manduca sexta para niños
