Observations with field-reared hornworms are consistent with the model: September hornworms receive more short-day cycles than August hornworms and thus have a shorter diapause.

Such manipulations consistently support a model in which diapause duration is inversely related to the number of short-day cycles received. The number of short-day cycles the hornworms receive can be varied by partial starvation and the use of different rearing temperatures.

Hornworms transferred from long-to short-day conditions at later stages of larval development enter diapause at a lower rate, but the resulting diapause is of greater duration. Short daylength throughout embryonic and larval development yields a high diapause incidence, but a diapause of short duration. If you live outside of Iowa please do not submit a sample without contacting the Plant & Insect Diagnostic Clinic.Daylength monitored by the embryos and larvae of the tobacco hornworm, Manduca sexta, is used to program both the incidence and duration of pupal diapause. Please see our website for current forms, fees, and instructions on preserving and mailing insects.Ĭontact information for each states diagnostic laboratory for U.S. The Iowa State University Plant & Insect Diagnostic Clinic will identify your insect, provide information on what it eats, life cycle, and if it is a pest the best ways to manage them. Do you live in Iowa and have an insect you would like identified? When hornworms are observed, handpicking is usually sufficient control action. Carefully watch for larvae and feeding from June to harvest. Parasitism and other natural factors keep hornworm populations sufficiently low in most gardens. Hornworms blend in with the foliage and are difficult to see until much defoliation has occurred.

Ravenous leaf feeding by hornworm larvae may result in extensive defoliation. A hornworm can eat a considerable amount of foliage that may look like severe damage, but actual yield loss is probably slight. The well–known tomato hornworm is more often a curiosity in gardens rather than a pest, though outbreaks have been known to occur. The larvae feed on the foliage for 4 to 5 weeks before growing to the commonly–seen size of 3 to 4 inches long. The adult hawk moths emerge in mid- to late June and lay eggs on the lower side of host plant leaves. The insect spends the winter in the soil as a large, brown pupa.

Both species have diagonal white stripes along the sides of the body. The short, slender horn on the tip of the abdomen is red on the tobacco hornworm and green on the tomato hornworm.

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