Tobacco and Tomato Hornworm on Vegetables

• Eggs are laid singly (not in clusters) on leaves, usually on the underside.
• Caterpillars have 4 to 5 instars as they mature over the course of about one month.
• Early-instar (recently-hatched) larvae have long horns, nearly the same length as the body, but the horns become proportionately smaller in later instars.
• Mature larvae that have finished feeding drop to the ground to pupate. They burrow about 4 to 6 inches deep into the soil but do not spin a cocoon.
• Pupae overwinter in the soil.
• Adult moths emerge over a long period, as early as May and extending as late as early August.
• One to two generations occur per year.

The adult moths are most active at sunset and again just before dawn, feeding on nectar from flowers. Larvae feed mainly on leaves, but can also chew into fruit. The older the caterpillar gets, the greater its appetite.

Host plants

Plants in the Solanaceae family: particularly tomato; less commonly on eggplant, pepper, potato. Tobacco hornworm, despite its name, is often found on tomato plants, and may be more commonly encountered than the tomato hornworm. As members of the Solanaceae family, petunia and calibrachoa plants can also be eaten by these hornworms.

Signs and symptoms

• Caterpillar feeding ordinarily begins at the top of the plant. 
• Caterpillars usually consume entire leaves, rather than chewing holes in them, and can rapidly defoliate plants.
• Caterpillars blend in very well, despite their eventual size, and damage is usually unnoticed until the final caterpillar instar (when 90% of defoliation occurs).
• Hornworms may chew into unripe fruits, and feeding damage on ripe tomatoes creates large gouges (especially during dry weather).

Monitoring

• Look for eggs under the leaves.
• Be alert for light feeding damage on the tops of tomato plants. As caterpillars grow, entire leaves and stems are eaten, leaving only stubs.
• Deer browsing damage will generally remove leaves on one side of the plant. Caterpillar damage (especially if there is more than one on the plant) will tend to be more concentrated on interior leaves, or it may be scattered across more of the canopy.
• Dark, blocky droppings (frass) on leaf surfaces or the ground under the plant indicate caterpillars feeding above. The larger the frass, the more mature the caterpillar (late-instar caterpillars produce pea-sized frass).

Prevention and control

• Spraying water on the plants can agitate the hornworms and make them easier to spot as they move.
• Remove caterpillars by hand and drop them into a container of soapy water. The feet on large caterpillars grip the plant strongly and make take some force to pull off.
• Large hornworms are often parasitized by small wasps. The cocoons of Braconid wasps look like grains of rice attached to the hornworm's back. (They are not eggs, which are too small to see and laid inside the caterpillar's body.) Do not kill parasitized hornworms: let the wasps complete their life cycle so they can continue to suppress new generations of caterpillars. A parasitized hornworm stops eating and eventually dies, so leaving it on the plant will not result in more damage.
• Hornworm damage rarely warrants the use of an insecticide.
• Tilling garden soil in the spring or fall may uncover and kill the pupae.