What are we looking for?
Hornworms can consume large portions of your tomato plants overnight, we are more likely to find tobacco hornworms manduca sexta since they are more prevalent in the Gulf Coast States. The tomato hornworm, Manduca quinquemaculata is typically found in the Northeast, although there is some overlap in the range of the two.
What does it look like?
Look for a round greenish caterpillar with five pairs of prolegs (protrusion like legs) and three pair near the head. It also has seven white diagonal stripes along its side. The white lines have black edging at the upper edges. The most identifiable characteristics is the pointed structure at the rear of the “horn” on a tobacco hornworm is red in color, while the “horn” on the tomato hornworm caterpillar is black.
Where should I look?
One thing to keep in mind is they prefer initially munching on the tender, upper portion of the plants. They will eat leaves, flowers and green fruit. The young caterpillars eat most and will devour entire leaves. 90% of the foliage consumption occurs during the first instar (smallest caterpillar) stage. When hunting for them pay close attention to the underside of the leaves especially along the midrib. When small the caterpillars can blend in with the plants midrib and can be easily missed.
Found them now what?
If you find them, you can spray the plant with a soft insecticide called BT (Bacillus thuringiensis). The spray is most effective on young, small caterpillars. Large caterpillars can be removed by hand.
There are many natural enemies including the Hymenopterous wasp pupae which feed on the hornworm. Keep on the lookout for hornworms with the many white “egg like” protrusions on the top and side. The white protrusions will turn into wasps that can parasitize other hornworms, but won’t bother you. Be on the lookout for this very hungry caterpillar as you can enjoy sweet, healthy tomatoes on your next salad or sandwich.