September 10, 2013 | Common Garden Pests
The tobacco hornworm, or Manduca sexta for those who still prefer latin, is the larval stage of the Carolina sphinx moths. Few people notice the adult M. sexta as it is an innocuous brown moth, but all tomato gardeners are familiar with the destructive tobacco hornworm. The tobacco and tomato hornworm (Manduca quiquemaulata) are often mistaken for one another as they look quite similar and feed on the same plants. The tobacco hornworm can have several lifecycles within a given year. M. sexta will over winter as pupae and emerge in the spring. The moths mate and lay eggs on a variety of cultivated plants including: tomatoes, potatoes, peppers, and tobacco. Tobacco and tomato hornworms can be distinguished respectively by their red and black horns. The eggs are deposited directly onto the food plant and caterpillars hatch about a week later. The tobacco hornworm is not very mobile and relies on it’s camouflage for protection. The caterpillars immediately begin to strip foliage from the plants and can completely destroy young plants if not stopped. After feeding the larvae pupate and emerge as moths again.
Naturally Controlling Tobacco Hornworms
The safest way to control tobacco hornworms is to remove them by hand (don’t worry they don’t bite or sting). Since the hornworm tends to feed on food plants conventional pesticides should be avoided entirely. Look for the hornworms clinging to the underside of stems around defoliated areas. While many suggest dropping the caterpillars into soapy water to kill them, we suggest a more gorilla warfare approach; hold them captive. The hornworms could be potentially carrying parasitic wasp larvae which you won’t be able to see until they have begun to pupate. Killing the caterpillar before they pupate kills the parasitic wasps which naturally help control the hornworm population. Instead of killing them immediately, simply take a large plastic yogurt container and cut a few large air holes (about half the size of your smallest captive). Next, add a moist paper towel and some tomato leaves if you’re feeling generous. Bring the container inside to keep a better eye on it, or leave it in the shade of the plant. After a couple days if wasp larvae are present they will emerge from the caterpillar and begin to pupate. The pupae will look like small, upright grains of rice on top of the hornworm. Place the caterpillars with evidence of parasitoids near your plants to emerge and protect your garden! They will still be alive but will be paralyzed and unable to feed anymore.
Don’t feel like getting that close and personal with this garden foe? Try cultivating your garden at the beginning and end of each growing year. This destroys the overwintering pupae.