![]() They initially feed on the upper portions of leaves and leave behind dark green or black droppings. The caterpillars constitute the damaging stage of these insects. ![]() The hornworm adults are nectar feeders and do not harm tomato and other related plants. Damage to tomato and related plants by hornworms There are usually two generations produced each summer larvae of the second generation overwinter as pupae. The caterpillars hatch and usually pass through five larval stages, or instars, in about one month. After mating, females lay small, pearl-like eggs individually on tomato foliage and leaves of other hosts. The moths of both species are very large with wingspans of up to five inches (Image 3), and are capable of flying long distances. The adult moths emerge in mid- to late spring. The full grown caterpillars that develop in mid- to late summer pupate and overwinter as pupae in a chamber located between four to six inches below the soil surface. The tomato hornworm has V-shaped white markings on its sides, and the horn is frequently black (Image 1). There are seven diagonal stripes on the sides of the tobacco hornworm, and its horn is usually red (Image 2). The caterpillars of tomato and tobacco hornworms both have five pairs of prolegs (note the large, fleshy prolegs on the tobacco hornworm in Image 2 being used to grip the leaf and stem of a tomato plant) and a horn on the last segment of the body. Besides tomato, these species also feed on pepper, potato, eggplant and some weeds of the nightshade family. However, the tomato hornworm also occasionally occurs as a “black” or dark form. Most of the time, both of these hornworm species are green. These two species of caterpillars are exceptionally large when full grown both develop to a length of three to four inches in approximately four weeks. The caterpillars, or larvae, of these two species are called hornworms because they possess a prominent “horn” on the hind end (see Images 1 and 2). There are a number of caterpillar pests of tomatoes in Michigan, but certainly the most well known and largest in size are two species of hornworms: the tomato hornworm, Manduca quinquemaculata, and the tobacco hornworm, Manduca sexta. Check the label of any pesticide referenced to ensure your use is included. Editor’s note: This article is from the archives of the MSU Crop Advisory Team Alerts.
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