common name: tobacco hornworm
scientific name: Manduca sexta (Linnaeus) (Insecta: Lepidoptera: Sphingidae)
common name: tomato hornworm
scientific name: Manduca quinquemaculata (Haworth) (Insecta: Lepidoptera: Sphingidae)
Introduction - Distribution - Description - Life Cycle - Host Plants - Damage - Management - Selected References
Tobacco and tomato hornworms are the common large caterpillars that defoliate tomato plants. Their large size allows them to strip a plant of foliage in a short period of time, so they frequently catch gardeners by surprise. They are quite similar in appearance and biology.
Figure 2. Newly hatched tobacco hornworm, Manduca sexta, larva and egg. Photograph by James Castner, University of Florida.
The tobacco hornworm is more common in the southern United States, especially the Gulf Coast States. Its range extends northward to New York. The tomato hornworm, in contrast, is uncommon along the Gulf Coast, and is more likely to be encountered in northern states. However there is some overlap in the ranges of the tobacco and tomato hornworm, and they may appear together on the same plant.
Eggs: Hornworm eggs are spherical to oval in shape, measure about 1.50 mm in diameter, and vary in color from light green to white. Eggs are deposited principally on the lower surface of foliage, but also on the upper surface. Duration of the egg stage is two to eight days, but averages five days.
Larva: The larva is cylindrical in form and bears five pairs of prolegs in addition to three pairs of thoracic legs. The most striking feature of the larva is a thick pointed structure or "horn" located dorsally on the terminal abdominal segment. The tobacco hornworm develops seven straight oblique whitish lines laterally. The white lines are edged with black on the upper borders, and the "horn" is usually red in color. The tomato hornworm is superficially similar, but instead of the seven oblique lateral bands it bears eight whitish or yellowish "V"-shaped marks laterally, and pointing anteriorly. The "V"-shaped marks are not edged in black. Also, in tomato hornworm the "horn" tends to be black in color. There normally are five instars, but occasionally six are observed. Corresponding mean larval body lengths are 6.7, 11.2, 23.4, 49.0, and 81.3 mm, respectively. Larval development time averages about 20 days.
Figure 2. Larva of tobacco hornworm, Manduca sexta (Linnaeus). Photograph by James Castner, University of Florida.
Figure 3. Tobacco hornworm larva
Figure 4. Last instar larva of the tomato hornworm, Manduca quinquemaculata (Haworth). Photograph by Paul M. Choate, University of Florida.
Figure 5. Tomato hornworm larva.
Pupa: Mature larvae drop to the soil at maturity and burrow to a depth of 10 to 15 cm, where they form a pupal cell. The pupa is large and elongate-oval in form, but pointed at the posterior end. It measures 45 to 60 mm in length. The pupa bears a pronounced maxillary loop, a structure which encases the mouthparts. The maxillary loop in tobacco hornworm extends back about one-fourth the length of the body, whereas in tomato hornworm it is longer, usually extending for about one-third the length of the body. The color of the pupa is brown or reddish brown. Duration of the pupal stage is protracted and variable.
Figure 6. Prepupa of the tomato hornworm, Manduca quinquemaculata (Haworth). Photograph by Paul M. Choate, University of Florida.
Figure 7. Newly formed pupa of the tomato hornworm, Manduca quinquemaculata (Haworth). Photograph by Paul M. Choate, University of Florida.
Figure 8. Late pupa stage of the tomato hornworm, Manduca quinquemaculata (Haworth). Photograph by Paul M. Choate, University of Florida.
Adults: The adults of both species are large moths with stout, narrow wings, and a wing span of about 100 mm. The forewings are much longer than the hind wings. Both species are dull grayish or grayish brown in color, though the sides of the abdomen usually are marked with six orange-yellow spots in tobacco hornworm and five spots in tomato hornworm. The hind wings of both species bear alternating light and dark bands.
Figure 9. Adult tomato hornworm, Manduca quinquemaculata (Haworth). Photograph by John Capinera, University of Florida.
Figure 10. Adult tobacco hornworm, Manduca sexta (Linnaeus). Photograph by John Capinera, University of Florida.
The number of annual generations is three to four in northern Florida, but two generations per year is common over most of the range of these species. The proportion of insects that enter diapause, which occurs in the pupal stage, increases from about 5% in June to 95% in mid August, as day length decreases. In northern Florida the insects are active from April to November, but they are abundant only for the first two generations because many pupae enter diapause. The life cycle can be completed in 30 to 50 days, but often is considerably protracted due to cold weather or diapause.
These insects feed only on solanaceous plants, most commonly on tomato and tobacco. They have been recorded on other vegetables such as eggplant, pepper, and potato, but this is rare. Several Solanum spp. weeds are reported to serve as hosts. Adults imbibe nectar from flowers of a number of plants, and can be seen hovering about flowers at dusk.
Larvae are defoliators, usually attacking the upper portion of plants initially, and consuming foliage, blossoms and green fruits. They usually consume the entire leaf. Because the larvae of hornworms attain such a large size, they are capable of high levels of defoliation. About 90% of the foliage consumption occurs during the final instar. Larvae blend in with the foliage and are not easy to detect. Thus, it is not surprising that they often are not observed until they cause considerable damage at the end of the larval period. Hornworms are not considered to be pests of commercial crops in Florida and only occasionally damage garden crops, probably due to the activities of natural enemies.
Figure 11. Defoliation of a tomato leaflet caused by tobacco hornworm, Manduca sexta. Photograph by James Castner, University of Florida.
Figure 12. Damage to tomato fruit caused by tobacco hornworm, Manduca sexta. Photograph by James Castner, University of Florida.
Insecticides: Chemical insecticides or the bacterial insecticide Bacillus thuringiensis are applied to the foliage for larval suppression (Creighton et al. 1961). The mature caterpillars are difficult to kill, so young larvae should be targeted. For additional information on chemical control, consult the Florida Insect Management Guide:
Cultural practices: The pupae are large and not buried very deeply in the soil, so greater than 90% mortality is caused by normal soil tillage practices. Hand picking and destruction of larvae is often practical in the home garden.
Moths are attracted to light and can be captured in light traps. Light traps have been used to attempt suppression of hornworm populations, and although some reduction was noted, this approach has not proved practical.
Biological control: Natural enemies of these pests are abundant. Polistes spp. wasps prey on the larvae and several wasp parasitoids (e.g., Trichogramma spp., Cotesia congregata, Hyposoter exigua) are sometimes effective. In Florida, Trichogramma pretiosum was released to control larvae at a rate of 378,000/acre at 3-day intervals and high levels of egg parasitism were attained.
Figure 13. Even though it is still capable of movement, this hornworm larva is already "dead." The white capsules on its back, frequently mistaken for "hornworm eggs" by many gardeners, are actually Hymenopterous wasp pupae of the Braconidae family. These wasps fed on the hornworm while in the larval stage and are now pupating into adults. When home gardeners find hornworms in this stage, they should let them be as they aren't capable of more damage. And when they emerge, the adult wasps will hunt for other hornworms to parasitize. Photograph by University of Florida.
To take advantage of the preference of Polistes wasps for hornworm larvae, wasp shelters or nesting boxes have been placed in tobacco fields to encourage the wasps, and wasp colonies were relocated to tobacco fields. Although wasp predation was inadequate in preventing damage to tobacco, this approach might be satisfactory for tomato crops.
- Fasulo TR. (2002). Vegetable Insects 1 and 2. Bug Tutorials. University of Florida/IFAS. CD-ROM. SW 173.
- Lange H, Bronson L. 1981. Insect pests of tomatoes. Annual Review of Entomology 26: 345-371.
- Madden AH, Chamberlin FS. 1945. Biology of the tobacco hornworm in the southern cigar-tobacco district. USDA Technical Bulletin 896. 51 pp.
- Metcalf RL, Metcalf RA. 1993. Destructive and Useful Insects: Their Habits and Control. McGraw-Hill Book Company, Inc. New York.
- Pohronezny K, Simone GW, Waddill V. 1980. A tomato scouting manual. University of Florida, IFAS.
- Wilkerson JL, Webb SE, Capinera JL. (2005). Vegetable Pests III: Lepidoptera. UF/IFAS CD-ROM. SW 182.