Pickleworm and Melonworm
Pickleworm, Diaphania nitidalis (Stoll); Melonworm, Diaphania hyalinata (Linnaeus), Pyralidae, LEPIDOPTERA


Adult - The pickleworm moth has a large, pale yellow spot near the center of each dark brown forewing; the pale yellow hind wings have a wide, dark brown border. Wingspan is about 32 mm. A cluster of dark brush-like hairs is present on the tip of the abdomen.

The melonworm moth has a brown head and a white-tipped abdomen with bushy hair-like scales. Its white wings have a narrow dark band around the margin and span up to 43 mm.

Egg - Deposited singly or in small clusters on the foliage, the white eggs gradually turn dull yellow before hatching. Variable in shape, each egg is about 0.5 mm in diameter.

Larva - About 1.5 mm long, the newly hatched pickleworm larva is almost colorless except for slightly darker jaws and a black spot on each side of the head. Third and fourth instar larvae are about 6 to 12 mm long and pale yellow with dark spots, each spot containing a large bristle. The dark-headed fifth instar larva has a yellow-green body with no spots and may be 25 to 30 mm long.

The slender, greenish melonworm larva has two thin white stripes down its back in all but its first and last instars. It is 25 to 30 mm long when fully grown.

Pupa - Enclosed in a thin silken cocoon, the white pupa turns reddish-brown soon after forming. Pupae are about 16 mm long.


Distribution - The pickleworm has been reported from Canada southward into South America. In this country it is a year-round inhabitant of southern Florida. Each summer the moth migrates into North Carolina, further northward into Iowa and Connecticut, and westward to Oklahoma and Nebraska. The melonworm, however, is rarely found north of the Gulf states.

Host Plants - These two caterpillars infest only cucurbits. Though the pickleworm prefers summer squash, it may severely damage cucumber and cantaloupe also. Watermelon, muskmelon, winter squash, pumpkin, and gourd are rarely damaged by this pest. The melonworm prefers foliage of muskmelon, squash, cucumber, and pumpkin. It very rarely attacks watermelon.

Damage - Unlike the melonworm which is primarily a foliage feeder, the pickleworm causes important economic damage to fruit. Young pickleworms usually feed for a time among small leaves at the growing tips of vines or within blossoms. A favorite place is the large staminate flower of squash where larvae hide under the ring of stamens at the base of flowers.

When about half grown, pickleworms normally bore into sides of fruits and continue to feed there causing internal damage and producing soft excrement. Both young and old fruits are attacked, but they prefer young fruits before the rind has hardened. Pickleworms make holes in the rind. After the rind has been punctured, the fruit soon rots, or, in the case of cantaloupes, becomes "sour." As the infestation increases, young fruits and flowers are damaged. Growing vines sometimes become riddles with holes and cease to grow.

Life History - Pickleworm moths migrate northward from Florida in the spring. They usually appear in the Raleigh area by early July. Eggs are deposited singly or in small clusters on hairy surfaces of plants. Approximately 3 days later young pickleworms emerge. After feeding for two weeks ore more larvae spin thin cocoons within rolled leaves and pupate. Five to 7 days later, a new generation of moths emerges. In North Carolina, pickleworms complete two full generations and a partial third, if food is available and there is no early frost. The life cycle of melonworms is similar.


In North Carolina, field experiments have shown distinct differences in susceptibility or resistance of cucurbit varieties to pickleworms. The more resistant squash varieties are Butternut 28, Buttercup, Boston Marrow, Blue Hubbard, and Green Hubbard. Gemini cucumbers, Edisto 47 and Honeydew cantaloupes, Blue Ribbon and Crimson Sweet watermelons, and Green Striped Cushaw, King of the Mammoth, and Mammoth Chili pumpkins also show good resistance to pickleworms. Tests with insecticides show much better control of pickleworms on resistant varieties than on susceptible varieties.

Insecticide applications should begin immediately when pickleworms or their damage appear. A few plants of a susceptible squash variety would help detect the first appearance of pickleworms, especially by the presence of insects in flowers. Make applications at weekly intervals after picking fruit and never just before. Apply in later afternoon to minimize bee kills. For recommended insecticides and rates, consult the current North Carolina Agricultural Chemicals Manual.

Return to AG-295 Table of Contents