Egg - The tiny oval egg is about 0.4 mm long. Light yellow when newly deposited, it turns pale orange before hatching.
Larva - The newly hatched larva is yellowish-gray and about 0.8 mm long. The mature fourth instar may be yellow, green, or ash gray and is covered with dark purple spots. Such a larva averages 6.5 mm long.
Pupa - A little over 6 mm long, the pupa gradually changes from green to brown. It occurs in the soil enclosed in a pupal cell made of loosely woven silk and covered with soil particles.
Host Plants - The tomato pinworm feeds only on solanaceous plants. Common hosts include crops such as tomato, potato, and eggplant. The weeds nightshade and horsenettle are also subject to attack.
Damage - Blotch-like leaf mines, folded and tied leaves, pinholes in stems and fruit, and fruit blotches all can be caused by pinworms. First and second instar larvae mine leaves in a manner similar to that of serpentine and vegetable leafminers. These mines, however, are widened gradually into one large blotch.
Upon emerging from leaf mines, third instar 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 rarely penetrate deeper than 18 mm and usually feed just below the skin. In addition to the presence of pinholes, injured tomato fruits have discolored blotches. Damage to leaves and vines is of little importance, but injury to the fruit can cause a substantial loss.
Life History - In California, Florida, Texas, and Mexico, tomato pinworms overwinter outdoors as pupae at or near the soil surface. In North Carolina and most other states, pinworms spend winter in greenhouses. The nocturnal moths may emerge as early as March or April. Eggs, usually deposited on the undersides of leaves, hatch about one week later. During summer, larvae mine the leaves for about 6 days and then fold leaves or bore into fruit for another 6 days. Mature fourth instar larvae either remain in folded leaves or drop to the soil to pupate. About 12 days later, a new generation of moths emerges.
In summer, a generation can be completed every 26 to 34 days. In cooler weather, the life cycle is longer. Seven to 8 overlapping generations occur each year in Florida. It is probable that just as many occur in North Carolina greenhouses. If moths escape to the outside, several generations may occur in field tomatoes during summer.
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