Cotesia congregata and other Braconidae
Braconid wasps- Kind
- Wild — attract it
- Best for
- Leave cocooned hornworms in place
Pest
Tomato hornworm
Manduca quinquemaculata
The short answer
A large green caterpillar, up to 10 cm long, with a horn on its last segment. It eats whole leaves and small stems and chews into green fruit, mostly in midsummer. Two species share the job: the tomato hornworm, commoner in the north, and the tobacco hornworm, commoner in the south. Hand-picking is the standard garden control — except for any hornworm carrying white cocoons, which should be left alone.
hero macro · late-instar larva on tomato stem
Late-instar Manduca quinquemaculata on a tomato stem, showing the white V-shaped marks and black horn. Photo: pending.
Identification
Up to 10 cm long and about 1.3 cm wide when full grown, bright green and very well camouflaged. Two species look alike. The tomato hornworm, Manduca quinquemaculata, has eight white V-shaped marks along each side and a black or dark blue horn. The tobacco hornworm, Manduca sexta, has seven white diagonal stripes and a red horn. Both feed on tomato, and in the south — Florida, for example — the hornworm on your tomatoes is usually the tobacco one, despite the name.
The caterpillar is easier to find by its signs than by sight. Look for dark green or black droppings on the leaves and ground, then search the stems directly above them; feeding usually starts high in the canopy. The adults are large grey-brown hawk moths with a wingspan of up to 12 cm: the tomato hornworm moth has five pairs of yellow-orange spots on the abdomen, the tobacco hornworm moth usually six.
Easily confused with
- Tobacco hornwormAlso a pestSeven diagonal white stripes on each side and a red horn. The tomato hornworm has eight V-shaped marks and a bluish-black horn. Both eat tomato and are managed the same way.
- Hornworm carrying white cocoonsBeneficial — leave itThe white bodies on its back are not eggs but cocoons of a parasitic Cotesia wasp. The hornworm is already dying: leave it, and the wasps that emerge attack other hornworms.
Damage symptoms
Hornworms usually eat whole leaves rather than chewing holes in them, and they can defoliate a plant quickly. Feeding tends to start high in the canopy and work down. At high numbers they strip plants and scar the fruit, and fruit they have fed on does not ripen properly.
- Whole leaves and small stems missing, often starting at the top of the plant
- Bare leaf midribs where the blade has been eaten away
- Large chewed gouges in green fruit
- Dark green or black droppings on leaves and on the ground below
- A caterpillar carrying white rice-like cocoons — parasitised, leave it
Lifecycle & degree days
The winter is spent as a pupa in the soil. Moths emerge from late spring to early summer, lay single eggs on the leaves, and the caterpillars feed for three to four weeks before burrowing down to pupate. The whole cycle takes about two months in summer, so the number of generations depends on how long the summer is — one in Massachusetts, two in most areas, and two to three in North Carolina. We have not found a degree-day model for garden use in the extension sources we checked.
- Larval feeding
- 3–4 weeks
- Egg to adult
- About 2 months in summer
- Generations / yr
- 1 (Massachusetts) to 2–3 (North Carolina); 2 in most areas
- Overwinters
- Pupa in the soil, 3–6 in (8–15 cm) down
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Host crops
Hornworms feed only on the nightshade family: in gardens mainly tomato, but also pepper, eggplant, potato and tobacco, plus weeds such as horsenettle and jimsonweed. Managing those weeds is one of the cultural controls extension services recommend.
Monitoring & action thresholds
Action threshold
No numeric threshold for gardens
UC IPM advises treating only when hornworms cause extensive leaf damage or feed on fruit, and UMass says there is no set economic threshold in tomato. The one published number we found is for tobacco fields (NC State): one hornworm over 2.5 cm without cocoons per 10 plants. That figure is not for gardens.
Check solanaceous plants regularly through the summer. Look for light feeding at the tops of the plants and for fresh droppings on the leaves and the ground. Search the stems above them, and check leaf undersides for single pale green eggs. Large droppings mean a large caterpillar. Before you remove anything, check its back: a hornworm with white cocoons is already dying and should stay where it is.
Beneficial
Biological control
Hornworms have natural enemies at every stage. Trichogramma wasps parasitise the eggs. Lacewing and lady beetle larvae eat eggs and young caterpillars, and paper wasps carry hornworms off to feed their young. The best-known enemy is Cotesia congregata, a braconid wasp that lays dozens to hundreds of eggs inside a young hornworm. Its larvae feed inside for about 12 days, then spin the white cocoons you see on the caterpillar's back. A parasitised hornworm eats about a fifth as much as a healthy one, and it dies. Leave it on the plant and the next generation of wasps will emerge from it. Where hand-picking is not practical, Bt works best while the caterpillars are still small, although UMass reports that it also works well on large hornworms.
Bacillus thuringiensis kurstaki
Bt (kurstaki)- Rate
- Label rate — ½–4 tsp per gallon on home concentrates; varies by product
- Best for
- Young larvae, when picking is impractical
Trichogramma spp.
Trichogramma wasps- Rate
- 50k–100k /acre weekly (1–2 /ft² in gardens)
- Temp
- 18–29 °C best; weaker at 15 °C
- Best for
- Eggs only — release while moths are laying
Cultural controls
In a garden, hand-picking is the most effective control and usually the only one needed. Everything else either reduces the next generation or protects the wasps that are already working for you.
- Hand-pick clean hornworms; a spray of water can help expose them
- Leave any hornworm carrying white cocoons — the wasps inside are the next generation of control
- Till or dig over the bed after harvest to destroy the pupae in the soil
- Pull horsenettle, jimsonweed and other nightshade weeds around the garden
- Rotate tomatoes and their relatives away from last year's bed
Chemical, last resort
Broad-spectrum sprays kill the wasps that finish off hornworms for you. Never spray open flowers: carbaryl is highly toxic to bees, and spinosad is toxic to bees until it driesCheck any product before it goes on. Open the compatibility matrix →
- Bt kurstakiREI 4 h
- SpinosadREI 4 h
- CarbarylREI 12 h
Rating: the effect on this pest's natural enemies if a spray hits them or they feed on treated plants. REI is the re-entry interval on farm and greenhouse labels; home labels usually give none, so follow the label.
Sources
UC IPM Pest Management Guidelines: Tomato — Hornworms (text updated 2013)
UC IPM, Relative Toxicities of Insecticides Used in Tomatoes to Natural Enemies (2016)
UC IPM Home and Landscape — Hornworms
University of Minnesota Extension, Tomato hornworms in home gardens (Hahn & Wold-Burkness, 2020)
UMass Amherst Extension, Tomato Hornworm fact sheet (updated 2025)
UF/IFAS EDIS EENY700, Tomato Hornworm (Byron & Gillett-Kaufman, 2018)
UF/IFAS EDIS EENY692, Tobacco Hornworm (Byron & Gillett-Kaufman, 2017)
NC State Extension, Tobacco Hornworms (Lopez, 2025)
University of Maryland Extension, Tobacco and Tomato Hornworm on Vegetables
Mississippi State Extension, Bug's Eye View: Cotesia congregata (Layton, 2020)
UF/IFAS Entomology, Cotesia congregata (Beneficial Arthropods gallery)
Page status
Drafted from the sources below, then checked claim by claim against those sources on 23 September 2026.
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