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Chance Hudnall, Carlton, Christopher E.
Manduca sexta, the tobacco hornworm (larvae) or Carolina sphinx moth (adults), is a large moth in the family Sphingidae (hawk moths or hummingbird moths). Larvae feed on plants in the family Solanaceae, including economically important crops such as tomatoes, peppers and tobacco.
Like most other larvae of the moth family Sphingidae, tobacco hornworms feature (and are named after) a tail horn at the rear end of their bodies. These spine-like horns are harmless to humans and are soft and flexible to the touch. At maturity, tobacco hornworm larvae have cylindrical, bright green bodies, up to 80 mm in length, that feature a series of seven white diagonals with black margins directed forwards. The tail horn is red to reddish brown in color. Fully developed pupae are reddish brown. Each pupa features a pronounced proboscis that forms a loop-like structure under the head. Tobacco hornworm adults possess a set of six pairs of orange-yellow bands on either side of the abdomen. The adult wingspan ranges from 9.5 cm to 12 cm. Mottled black, brown and white markings are present on the forewing. The hindwings are black and white with two median black lines that form a zigzag. A long tongue is coiled beneath the head, a character shared with other members of the family Sphingidae and other families of Lepidoptera.
A similar species with similar habits also occurs in Louisiana. Manduca quinquemaculata, the tomato hornworm (larvae) or five-spotted hawkmoth (adults) possesses a few key differences that allow the two species to be differentiated. The tail horn of tomato hornworms is black rather than reddish, and seven to eight, rather than six, white V-shaped markings are present on each side of the body. The abdomen of the adult moth bears five orange-yellow bands, one fewer than the Carolina sphinx moth.
Manduca sexta undergoes two generations per year in northern parts of its range, three or more in the south, including Louisiana. The life cycle requires 30 to 50 days to complete, depending on season, with warmer temperatures speeding up the process. Female moths deposit eggs on the underside of plant leaves. Larvae hatch in two to four days and immediately begin feeding on host plants in the family Solanaceae. During the next 15 to 20 days, the larvae undergo roughly five growth stages (instars). Mature larvae begin wandering in search of soft soil to burrow into, then pupate underground, a process that may require a week to complete. Adults emerge one to two weeks later during warm weather or remain in the pupal stage during the winter and emerge during spring. Within just a few days of emergence, females mate and may lay more than 1,000 eggs during their life spans. Adults feed on nectar and individuals are often seen hovering in front of long-throated flowers and extending their long tongue (proboscis) to access nectar.
The tobacco hornworm occurs throughout North and South America, as far north as southern Canada, south to Argentina. Larvae of both species of Manduca may be pests of crops in the family Solanaceae in Louisiana. In Louisiana these include tomatoes, peppers, potatoes and eggplants. They also feed on several wild hosts such as jimsonweed and are serious pests in tobacco growing regions. Tobacco hornworms are unique in their ability to metabolize nicotine as a defense against potential predators. If left unchecked, crops can be defoliated by the large larvae in a relatively short amount of time. The caterpillars are a difficult problem for home gardeners because young larvae are often overlooked, grow rapidly and consume enormous amounts of plant material as they mature.
Several methods are utilized in managing hornworm populations. In home gardens, manually searching for plant damage and small larvae, then hand-picking the larvae is a simple but effective control method. Searching under plants for the large fecal pellets (frass) may lead to discovery of the camouflaged larvae in foliage. For larger commercial operations, chemical or augmented biological control may be required. Biological control occurs naturally, typically by braconid wasps in the genus Cotesia, so chemical controls should be used only as a last resort since they also kill these beneficial wasps. Female wasps pierce the caterpillar’s body and deposit eggs. The wasp larvae hatch and feed internally on body tissues. After completing development, the wasp larvae exit the body and pupate within a small white cocoon. Large caterpillars may bear several dozen of these wasp cocoons, which are often mistakenly assumed to be eggs. Adult wasps eventually emerge and infect other caterpillars. Parasitized hornworm larvae do not survive to adulthood.
Larva of Manduca sexta (Kimberlie Sasan, iNaturalist, (Creative Commons BY-ND 4.0).
Adult of Manduca sexta (Lena Zappia, iNaturalist, Creative Commons BY-NC 4.0).
