Description: Early instar caterpillars range in color from white to yellow. As they molt and grow, tomato hornworm caterpillars turn to green with 8 v-shaped white marks on each side of their bodies. Tobacco hornworms differ slightly, having 7 diagonal white marks down each side instead. Both tomato and tobacco hornworms have a hornlike projection on their last segments – thus the name hornworm. Both pests are the larvae of sphinx moths, fat-bodied moths with small forewings. Eggs are oval and green, and laid singly on leaf surfaces.
Life cycle: Both tomato and tobacco hornworms overwinter in the soil as pupae. In spring, adults emerge from the ground to mate and lay eggs. When garden crops are not yet available, the adult moths will lay their eggs on other solanaceous plants, including weeds like jimsonweed, nightshade, and horse nettle. Caterpillars feed on foliage, reaching maturity within 4 weeks. The larvae then drop to the ground and pupate. A second generation of moths in midsummer, just when tomatoes and other nightshade crops are beginning to flower. These second generation caterpillars tend to do the most damage in the garden, before pupating in the soil in fall.
Crops damaged: Tomatoes, potatoes, eggplants, and peppers. Caterpillars feed on foliage and sometimes on unripened fruit.
Signs and symptoms: Defoliation of host plants, especially near the top of the plants. As caterpillars get larger, defoliation accelerates and entire plants can be devoured quickly. Frass (black or green caterpillar droppings) on lower leaves or on ground under affected plant.
- Hand pick caterpillars and drop them in soapy water to destroy them. This requires a good eye, as hornworm caterpillars are well camouflaged.
- Turn or till soil at the end of the season to disturb any burrowing caterpillars or pupae.
- Keep the garden free of solanaceous weeds that provide tomato and tobacco hornworms additional hosts.
- Apply Bacillus thuringensis when larvae are young.
- Attract beneficial insects, such as predatory wasps and lady beetles, that feed on eggs and young caterpillars.
- Braconid wasps parasitize hornworms. If you find a hornworm with white, cylindrical projections on its body, leave it in the garden. These are braconid wasp pupae, and more parasitic wasps will emerge from them and find other hornworms to parasitize.