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

Introduction

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.

Distribution

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, but relative to tobacco hornworm is more likely to be encountered in northern states. They both occur in many areas, and may appear together on the same plant.

Description

Egg. 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.

egg

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.

tobacco hornworm larva


tobacco hornworm larva

tomato hornworm larva


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.

tomato hornworm prepupa

newly formed tomato hornworm pupa

late stage tomato hornworm pupa

Adult. 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 bears alternating light and dark bands.

adult tomato hornworm

adult tobacco hornworm

Life Cycle

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.

Host Plants

These insects feed only on solanaceous plants, most commonly on tomato and tobacco. They are recorded from 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.

Damage

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.

defoliation

fruit damage

Management

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:

Insect Management in tobacco
Insect Management for tomatoes, peppers, and eggplant

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 also 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.

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 into tobacco. Although wasp predation was inadequate to prevent damage to tobacco, this approach might be satisfactory for tomato.

hornworm parasites

Selected References

Author: Raul Villanueva, University of Florida
Photographs: Paul M. Choate, James Castner, and John L. Capinera, University of Florida
Project Coordinator: Thomas R. Fasulo, University of Florida
Publication Number: EENY-31
Publication Date: June 1998. Latest revision: January 2007.
Copyright 1998-2007 University of Florida

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Department of Entomology and Nematology
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