TOBACCO HORNWORM AND AN ENEMY

A, Parasite cocoons and adult on hornworm (greatly magnified); a, hornworm eggs; b, young larva; c, mature larva; d, pupa; e, adult moth. (All stages of horn-worm about natural size.)

TOBACCO HORNWORM

The tobacco hornworm, like the tomato hornworm, which it closely resembles, feeds voraciously on the leaves of tobacco, tomato, and related plants. Because of its large size and appetite, even a few horn-worms can destroy the plants.

The parent of the tobacco hornworm is a large hawk-moth, which in flight is sometimes mistaken for a hummingbird. The eggs are laid on the under side of the leaves. In about a week a tiny hornworm emerges from the egg. It feeds on the leaves until it reaches full growth in about 3 or 4 weeks. The mature hornworm burrows several inches into the soil and enters the pupal, or resting, stage. It ordinarily remains inactive 2 to 4 weeks, although this stage may last until the following spring. When the moth emerges from the pupal cell, it leaves the soil to mate and lay eggs for the next brood.

Control: Despite its large size and formidable-appearing horn, the hornworm is an easy prey to its natural enemies. The half-grown hornworm is the victim of a tiny wasp (Apanteles congregatits),which hunts it down and lays its eggs within the hornworm's body cavity. As many as 377 grubs of this wasp have been found feeding within a single hornworm. The grubs mature in a week or two and form white cocoons attached to the back of the weakened hornworm, giving it an appearance of being covered with tiny eggs. The parasitized hornworm becomes weaker and more sluggish and soon dies. The mature grubs of the wasp usually remain in the cocoon for 3 or 4 days, and then enter the pupal stage, which also lasts 3 or 4 days, after which the adult wasp emerges. Some of the grubs, however, do not pupate until the following spring, but remain in cocoons that have fallen to the soil and become protected by debris.

The wasp and other natural enemies do much to reduce hornworm numbers, but they cannot be depended on to prevent damage to tobacco or tomato. When control measures are necessary, one of the following should be used:

Destroy tobacco plants as soon as the crop is harvested.

Hand-pick the hornworms from infested plants in small plantings.

Apply 10 percent TDE dust at 30 pounds per acre per application.