Hornworms
Click for larger image Tobacco hornworm (Lepidoptera) on tomato (Lycopersicon); note reddish colored spike or "horn" at tail end that gives the hornworm its name

The tomato hornworm, Manduca quinquemaculata, and the tobacco hornworm, M. sexta, are common pests of tomato, tobacco, eggplant, pepper, and potato throughout most of the United States. The hornworms are large (up to 4 inches long), bright green caterpillars with diagonal white stripes and a prominent horn at the rear. The two species have slightly different markings. The tomato hornworm has 8 diagonal white stripes on each side; the horn is straight and black. The tobacco hornworm has 7 diagonal white stripes; its horn is curved and red.

Symptoms and Diagnosis

Larvae of both species consume entire leaves and small stems and may chew large pieces from green fruit. Hornworm damage is obvious when the infestation is moderate to heavy because of the large amount of defoliation. Search for the large caterpillars. Large, black droppings on the leaves or ground beneath the plant will usually indicate the presence of hornworms.

Life Cycle

Hornworms overwinter in the soil as hard-shelled, brown pupae. Large adult moths, known as sphinx or hummingbird moths, emerge in May or June and deposit spherical green eggs on the undersides of leaves of host plants. The larvae hatch a week later and feed on foliage and fruit for three to four weeks until reaching full development. Pupation occurs in the soil and adults emerge 2 to 4 weeks later to lay second generation eggs. In Missouri there may be one or two generations depending on location.

Integrated Pest Management Strategies

1. Handpick caterpillars. Handpicking is usually all that is needed to control these pests in a home garden. Larvae are most easily located in early morning, often on the exterior of the plant. Leave any caterpillars with small white cocoons on their backs; they are being parasitized by a braconid wasp, which will soon produce more wasps to control them.

2. Biological control. Bacterial insecticides containing Bacillus thuringiensis kurstaki (Btk) are effective when larvae are smaller. It may take several days for the caterpillars to die, but feeding generally stops shortly after treatment.

3. Cultivation. Disking or rototilling after harvest destroys pupae in soil, reducing overwintering numbers.

4. Chemical control. An application of carbaryl (Sevin) or permethrin will effectively control hornworms if handpicking is impractical. However, chemical control will also reduce the numbers of beneficial insects.

Organic Strategies

Strategies 1 and 3 are strictly organic approaches. For an organic approach to Strategy 2, consult the Organic Materials Review Institute (OMRI™) for appropriate Bacillus thuringiensis (Bt) products.

More images:

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The caterpillar/larva of this snowberry clearwing moth (Lepidoptera) feeds on dogbane, honeysuckle and snowberry. Here, it is resting on Joe Pye weed (Eupatorium)
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Look closely. This tobacco hornworm (Lepidoptera) blends perfectly with the color of its tomato host (Lycopersicon). The white cocoons of the parasitic braconid wasps (Hymenoptera) on its back stand out.
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Tobacco hornworm (Lepidoptera) eaten alive by parasitic braconid wasps (Hymenoptera) in the white cocoons on its back
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Pink-spotted hawkmoth (Agrius cingulata), the adult form of a sweet potato hornworm (Lepidoptera)
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Pink-spotted hawkmoth (Agrius cingulata), the adult form of a sweet potato hornworm (Lepidoptera)
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Pink-spotted hawkmoth (Agrius cingulata), the adult form of a sweet potato hornworm (Lepidoptera) sipping nectar from a moonflower (Ipomoea)
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Pink-spotted hawkmoth (Agrius cingulata), the adult form of a sweet potato hornworm (Lepidoptera) sipping nectar from a moonflower (Ipomoea)
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Tobacco hornworm (Lepidoptera) on tomato (Lycopersicon) with parasitic braconid wasps (Hymenoptera) in the white cocoons on its back
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Hornworm (Lepidoptera) eaten alive by parasitic braconid wasps (Hymenoptera) in the white cocoons on its back
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Tobacco hornworm (Lepidoptera) on 'Fish' pepper (Capsicum)
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Close-up of tobacco hornworm (Lepidoptera) on 'Fish' pepper (Capsicum)
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Tersa sphinx moth; larval food include pentas and catalpas
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Tersa sphinx moth; larval food include pentas and catalpas
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This snowberry clearwing moth (Lepidoptera) feeding on butterfly bush (Buddleja) is a kind of sphinx moth & a close relative of the sphinx moths whose larvae are the tomato & tobacco hornworms
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This day-feeding snowberry clearwing moth or bumblebee moth (Lepidoptera) is sipping nectar from a butterfly bush (Buddleja davidii); unlike this moth, most moths feed at night
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Pupa of a hornworm/sphinx moth (Lepidoptera)
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Pupa of a hornworm/sphinx moth (Lepidoptera)
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Parasitized tobacco hornworm (Lepidoptera) on tomato (Lycopersicon); note braconid wasp cocoons along back of caterpillar
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The pink-spotted hawkmoth or Agrius cingulata (Lepidoptera) is a pollinator of deep-throated flowers, but in its larval form, it is a hornworm caterpillar that feeds on sweet potatoes and related plants
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Hornworms (Lepidoptera) feed on foliage but may also feed on the tomato fruit (Lycopersicon).
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White-lined sphinx moth (Lepidoptera). Adult feeds on nectar; caterpillars feed on a variety of hosts, including apple, grape and tomato
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Close-up of white-lined sphinx moth (Lepidoptera)