Primarily solanaceous plants such as tobacco, tomato, eggplant, pepper, potato, and certain weeds.
The larval stage is a large (up to 3 1/2 to 4 inch long) green caterpillar with white and black markings on each side of the body. One of the last abdominal segments has a spine-like red (Tobacco hornworm) or black (Tomato hornworm) horn that gives this insect its' name. The adult is gray or brown in color with a wing spread of 3 to 5 inches and 5-6 pairs of yellow or orange spots on the abdomen.
The larvae consume large amounts of foliage and can virtually defoliate even large plants. Will feed on fruit if most of the leaf material has been consumed. Plants will be seen with many stems and leaf veins, but with the leaf surfaces completely removed. Rather than boring into the fruit, they feed superficially leaving large, open scars.
In small plantings, hornworms can be controlled simply by picking the larvae off the plants. Also, the bacterial insecticide, Bacillus thuringiensis can be used to control this pest.
Tachinid flies resemble the common housefly but are a little larger. Other tachinids look like bees or wasps. They cause no damage to plants. Most tachinid flies lay eggs directly on the body of the host insect. After an egg hatches, the larva burrows into the body of the host and feeds inside. When fully developed, the larva chews its way out, drops to the ground, and pupates in the soil. Tachinid flies are beneficial insects. Parasitized hornworms are easily recognized by the small white oblong cocoons attached to their backs. Such worms should be left in the garden so the emerging insects can parasitize other hornworms.