Insects – Tobacco and Tomato Hornworm
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Tobacco feeding hornworms include 2 species, the tobacco hornworm (Manduca sexta) and the tomato hornworm (Manduca quinquiemaculata). These species are biologically similar but easily distinguished from one another both as larvae and adults. Larval tobacco hornworms have 7 diagonal stripes on each side and a red posterior horn, while larval tomato hornworms have 8 chevrons on each side and a bluish black horn. Tobacco hornworm moths have 6 orange spots on their abdomen, and tomato hornworm moths have 5 spots. The pupae of both species are dark brown and have a handle-like tongue case on the exterior. Hornworms overwinter as pupae in the soil. Adults begin to emerge in early June, and most of the damage occurs in July and later. Two to three hornworm generations occur in North Carolina, depending upon temperature.
Larvae feed on several solenaceous crop species, including tobacco and tomato, as their names suggest. Hornworms progress through 5 to 6 larval instars, with the majority of feeding occurring at fifth or sixth instar. Voracious feeders, two hornworm larvae are capable of completely defoliating a tobacco plant, and moderate populations in a field can result in significant damage.
Thresholds and Management
Treatment is justified when one or more hornworms larger than 1 inch and without parasite cocoons (Cotesia congregata) are found per 10 plants checked. Since larvae with parasite cocoons eat much less, they should be counted as 1/5 of a caterpillar, meaning five worms with cocoons equal one healthy worm.
See the North Carolina Agricultural Chemicals Manual for registered materials and use recommendations.
Many native biological control agents feed on hornworms in North Carolina, and these predators and parasites play an active role in reducing the damage hornworms cause. The most obvious hornworm parasitoids are Cotesia congregata. These wasps lay their eggs inside of first to third instar hornworm larvae. As the caterpillars mature, so do the wasp larvae. The wasp larvae then emerge from the fourth or fifth instar hornworm and pupate in white cocoons on their backs. A parasitized hornworm eats roughly 1/5 that of a non parasitized worm.
Stilt bug adults and nymphs (Jalysus spinosus) feed on both tobacco budworm and hornworm eggs. Many species of wasps (Polistes spp.) use hornworms and other caterpillars as food for their larvae. Tachinid fly parasitiods (Winthemia spp. and Archytas marmoratus) also attack hornworms, killing them in the pupal stage.