Manduca sexta is a moth of the family Sphingidae present through much of the Americas. The species was first described by Carl Linnaeus in his 1763 Centuria Insectorum.
Commonly known as the Carolina sphinx moth and the tobacco hawk moth (as adults) and the tobacco hornworm and the Goliath worm (as larvae), it is closely related to and often confused with the very similar tomato hornworm (Manduca quinquemaculata); the larvae of both feed on the foliage of various plants of the family Solanaceae. The larvae of these species can be distinguished by their lateral markings: Tomato hornworms have eight V-shaped white markings with no borders; tobacco hornworms have seven white diagonal lines with a black border. Additionally, tobacco hornworms have red horns, while tomato hornworms have dark blue or black horns. A mnemonic to remember the markings is tobacco hornworms have straight white lines like cigarettes, while tomato hornworms have V-shaped markings (as in "vine-ripened" tomatoes). M. sexta has mechanisms for selectively sequestering and secreting the neurotoxin nicotine present in tobacco.
M. sexta is a common model organism, especially in neurobiology, due to its easily accessible nervous system and short life cycle. Due to its immense size M. sexta is big enough for medical imaging modalities (like CT, MRI, or PET) and used as a model in imaging and gut inflammation. It is used in a variety of biomedical and biological scientific experiments. It can be easily raised on a wheat-germ-based diet. The larva is large, and thus it is relatively easy to dissect it and isolate its organs.
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Tobacco hornworms are facultative specialists; the larvae can grow and develop on any host plants. However, the larvae prefer solanaceous plants, such as tobacco and tomato plants. On these types of plants, larvae grow and develop faster. The lateral and medial sensilla styloconia (sensory receptors) on their mouthparts help them to identify solanaceous plants by recognizing indioside D, a steroidal glycoside found in those particular plants (del Campo et al., 2001). Salicin is a distasteful phagodeterrent, found only in Salix spp. while caffeine is a phagodeterrent that is actually toxic. Schoonhoven 1969 found that M. sexta habituation to salicin is mediated by desensitization of the deterrence associated peripheral neurons and Glendinning et al 1999 the same for caffeine. However Glendinning et al 2001 find only a small peripheral desensitization for salicin, concluding that Schoonhoven erred, and that habituation in this case is centrally mediated. Tobacco hornworms are considered pests because they feed on the upper leaves of tobacco plants and leave green or black droppings on the plants. As adults, they do not damage plants since they feed on nectar.
Tobacco hornworm larvae prefer humid environments. When dehydrated, tobacco hornworm larvae will move towards a source of water or to an area with a high relative level of humidity. They use their antennae to locate water to drink.
M. sexta has a short life cycle, lasting about 30 to 50 days. In most areas, M. sexta has about two generations per year, but can have three or four generations per year in Florida.
