Pinworms feed only on solanaceous plants. Common hosts include tomato, potato, and eggplant.
Newly hatched larvae are yellowish gray. Mature larvae may be yellow, green, or ash gray and have dark purple spots on the body. They are about 1/4 inch long. The tomato pinworm can not overwinter outdoors in Oklahoma but may be active year-round in greenhouses. There can be 6 to 8 overlapping generations per year in greenhouses.
First and second instar larvae mine the leaves. The mines are widened gradually into one large blotch. Older larvae fold and web leaves to protect themselves and feed from inside these shelters. Some of the larvae bore into stems, buds, and fruit leaving small "pinholes" on the surface. The fruit usually is entered near calyx lobes or the stem. Larvae usually feed just below the skin. In addition to the presence of pinholes, injured tomato fruits have discolored blotches.
Sanitation and prevention are good control measures for tomato pinworms. Close inspection of new plants can prevent serious problems later in the season. Pinworms are difficult to control when heavy infestations have been allowed to develop.