In some years there are so few larvae, I don’t have to treat at all. Treating tomato plants with an insecticide (aimed at controlling hornworms) earlier than July is wasteful, so I don’t bother. They kill only caterpillars, and only when the caterpillars EAT the sprayed leaves. There are insecticides with this killing agent that are approved for organic gardeners. When I start seeing them, I treat my tomato plants with a biological insecticide containing spores and protein crystals of a bacterium named Bacillus thuringiensis. To me, the best plan for controlling the larvae is to watch for the first tiny larvae, starting in early July. Small caterpillars eat relatively little leaf area, but the older ones consume huge quantities of foliage, and sometimes damage the fruit. White cocoons of Apanteles wasps are on this tabaco hornworm larva. But that does not change the general pattern that we rarely find eggs before July. That combination occasionally produces New Hampshire adults in June. Today, occasionally we find a tomato greenhouse where the soil did not freeze over winter, and the insects were not well controlled. Therefor, this species formerly was not found here until late June or July each year, when the first adults flew to New Hampshire from farther south.

The pupae of neither species can survive New Hampshire winters (where the soil freezes). The long mouthparts project like the handle of an acient Greek amphora. Pupae of hornworm moths (the family is called sphinx moths) are large and brown. When fully grown, the larva drops off the plant and burrows into loose soil, where it pupates. The tomato hornworm has v-shaped white markings on the sides, and the horn on older larvae is often blue-ish. Tobacco hornworm has diagonal white markings on its side, and the older caterpillars often develop red color on the “horn”. The two species are easy to tell apart in the caterpillar stage. When they have fully grown, they can be over three inches long. At first, they make small holes in the leaves, but as they get larger, they end up eating the entire leaves, leaving behind the main mid-rib. The caterpillars begin feeding on leaves. After several days, the eggs hatch into tiny caterpillars, each with a very long “horn” at the rear end. Eggs are about 2mm long, and are about the same green color as tomato leaves.

Download tobacco hornworm moth