Manduca quinquemaculata
Late July and early August are usually the time when we see tomato hornworms. Despite typically appearing in lower numbers compared to other major pests, these large caterpillars consume large amounts of foliage on peppers, tomatoes, eggplant, and potatoes, and can cause impressive feeding damage.
There are two species of hornworm that feed on tomatoes: tobacco hornworm (Manduca sexta) and tomato hornworm (Manduca quinquemaculata). The two are very similar in appearance, life cycle, and feeding behavior.
Identification
- Eggs: Spherical, greenish yellow eggs are laid on the undersides of host plant leaves.
- Larvae: Caterpillars of both species are green with a distinct "horn" on the top of the tail end. The horn of the tobacco hornworm is red, while the horn of the tomato hornworm is dark blue or black. may reach 4 inches in length and 1/2 inch in width when fully grown. Both species also have a series of white stripes along their sides; tobacco hornworms have black margins along the white stripes, while tomato hornworms have green margins along the white stripes and stripes are more v-shaped.
- Pupae: Larvae develop into dark brown, two-inch long pupae. A sheath for the mouthparts projects from the head of the pupa and curves downward, resembling the handle of a pitcher.
- Adults: Adults are large moths, predominately gray or gray-brown with lighter markings. They are commonly referred to as sphinx, hawk, or hummingbird moths. The adult tomato hornworm is known as the five-spotted hawk moth while the adult tobacco hornworm is called the Carolina sphinx. The wingspread may reach five inches and the hairy, robust abdomen has yellow spots. The moths are commonly seen at dusk, hovering hummingbird-like over beds of petunias and other flowers with long corollas and extracting nectar using their long, coiled, tube-like mouthparts.
Life Cycle
There is one generation per year in Massachusetts. Adult moths emerge in late spring to early summer and lay eggs singly on the undersides of host plant leaves. The eggs hatch in approximately one week and larvae begin feeding on foliage. Larvae typically feed for 3-4 weeks, and molt five times. Once the larvae are fully grown, they burrow 3-4 inches into the soil to pupate and overwinter before emerging as adults the following year.
Crop Damage
Hornworms do not appear in large densities compared to many other major pests, but each caterpillar requires a significant amount of food to grow to its full size and can eat entire leaves and cause severe defoliation to a few plants. Hornworms may also chew on tomato fruit but do not tunnel deep into the fruit.
Monitoring & Thresholds:
Scout by searching leaves for larvae, heavy chewing damage, or large quantities of frass. The larvae blend in well with tomato plants, so you may see defoliated stalks or the characteristic dark-green droppings (fecal pellets) before the caterpillar is located. An ultraviolet flashlight can also make caterpillars easy to locate as the larvae fluoresce under UV light.
There is no set economic threshold for this pest in tomato. Where damage is unacceptable, or if there are high numbers, foliar sprays can be used.
Biological Controls:
The parasitoid braconid wasp Cotesia congregata is an important and fairly common natural enemy of tomato and tobacco hornworms. The wasps lay their eggs inside the body of the caterpillars. After feeding within the caterpillar body, the larvae of the wasps eat out through the skin and spin cocoons on the caterpillar surface. One hornworm can be host to dozens of wasps at once. The adult wasps later cut out circular lids and escape from the cocoons to attack other hornworms. Avoid hand-picking or killing parasitized hornworms to encourage populations of their natural enemies.
Chemical Controls & Pesticides:
Using selective insecticides will conserve beneficial insects which help keep hornworm populations under control. OMRI-listed products in high tunnels include products containing the active ingredients Bacillus thuringiensis (Bt) kurstaki or aizawa strains and spinosad. Although Bt usually works best on small larvae, in this case it will work very well even against large hornworms. Indoxycarb, and tebufenozide are conventional selective insecticides which can be used for outdoor tomatoes. In peppers, any controls used for European corn borer should control hornworms.
For current information on production methods (including varieties, spacing, seeding, and fertility), weed, disease, and a full list of options for chemical insect management, see the New England Vegetable Management Guide section on greenhouse & high tunnel tomato insect control or outdoor tomato insect control.