Identification
Tomato pinworm caterpillars are tiny and have a mottled pattern. Caterpillars may sometimes be quite dark.
Early instars of pinworm are light colored and appear smooth. They lack the obvious tubercles and bristles of newly hatched tomato fruitworms. Later instars, the stages most often found in fruit, are usually gray or yellowish with an irregular band of red or purple across each segment. The slender, brown pupa is usually enclosed in a loose silk cocoon with adhering soil or plant debris. Adult moths are light gray, peppered with small black flecks, and can be confused with the potato tuberworm. Don't confuse leaf damage with mining of leafminers, which is narrow and meandering, with a dark line of feces threaded through it. Leafminers never fold leaves.
Life Cycle
Eggs are laid on lower surfaces of leaves. Larvae usually begin to feed in leaf mines before moving to fruit. Larvae may complete development in leaf shelters, or they may leave to enter fruit, later pupating on the ground or in soil. Adults, which emerge from pupae after a few days, are active mostly at night. Mating occurs soon after emergence and females lay most of their eggs within 2 days. There can be as many as seven or eight overlapping generations per year; the life cycle takes less than a month in summer, but may take 3 to 4 months in winter. In mild winters, development continues as long as host plants are available; there is no diapause.
Damage
Pinworms cause leaf mines and folded shelters on leaves. They bore into fruit at the stem ends, creating narrow, blackened tunnels. Damage is hard to detect at first, but after larvae have been feeding for some time, a brown, granular frass usually appears at the edge of the calyx.
Solutions
Tomato pinworms are difficult to control with insecticides, and natural enemies are not effective. Disc all plants immediately after harvest. A host-free period of 3 months or more is essential to control pinworms.
