Tomato Hornworm: Hawk Moth
The tomato hornworm is a large, scary, green apparition that can appear on tomatoes or grapes, defoliating a plant by chewing through the leaves in a matter of a few days. It gets its name from the large horns that protrude from the last segment.
The Manduca quinquemaculata - tomato hornworm - is the larval state of a moth called Lepidoptera sphingidae or more commonly, hummingbird moth. (In some places it is also known as the sphinx, or hawk moth.) As an adult moth, it has a wingspan of 5 or six inches, is grey or brown in color with yellowish spots. The back wings have striated dark and light brown colors.
The adult stage of the hummingbird moth is used primarily for mating and laying eggs. The moth lays the eggs singly on both the upper and lower sides of the leaves of a variety of plants that might serve as food for hatching larvae. The eggs generally hatch in six or eight days after laying, (usually in two batches, the first occurs in late spring). The original eggs are only 1/10th of a centimeter (just a fraction of an inch) around when laid.1
The hornworm larvae come out of the egg eating. They are voracious and will consume any solanaceous plant (members of the nightshade family of plants). Their favorite is, of course, tomato, but will also attack peppers, potatoes, grapes, and eggplants in the garden. They are also fond of some weeds including, jimsonweed, horsenettle, and nightshade.
Tomato hornworms go through five larval stages, in the most conspicuous stage it is bright green in color with "V" shaped marks on eight of the segments. It has a large black horn on the final segment. The "caterpillar" grows to be about four inches in length in about four weeks. One tomato hornworm can devastate a plant, consuming most of the foliage and even some of the green fruit. Because of their green color, they blend well with their environment and are not often noticed until they have wreaked significant damage in the garden.
When the tomato hornworm has reached full growth, it will drop from the plant and burrow into the soil to pupate. After about two weeks in mid-summer, moths will emerge from the soil to begin again the process of mating and laying eggs. These creatures get in about two life-cycles per year. On the later cycle, the pupae remain under the soil all winter.
Most tomato hornworm infestations like other attacks by leaf eating insects in large agricultural fields are not large enough to warrant large scale controls. Nevertheless, the larvae can be particularly devastating to small gardens. The best control is to pick off individual hornworms and drop them into a solution of salt water, or simply step on them. Tilling the soil around the plant when it is time for them to go under the soil will destroy up to 90% of the larvae.
The braconid parasitic wasp is a natural enemy of the tomato hornworm. It will lay its eggs on the back of the worm. The larvae of the wasp burrow into the hornworm and feed from it internally, killing it in the process. They then become wasps themselves and emerge to seek out more hornworms. The common wasp will also attack and consume the larvae. In the egg stage the hornworms are also attacked by ladybugs and green lacewings.
- University of Minnesota