Common name: Melonworm

Scientific name: Diaphania hyalinata

Distribution

Melonworms are tropical insects and cannot tolerate cold temperatures. They occur throughout most of Central and South America, the Caribbean, south Florida and south Texas where they live year-round. The melon

Melonworm moth.

Melonworm moth.

worm travels northward during the summer months where it can be found in the southeastern states, though occasionally it disperses north to New England and the Great Lakes region. Melonworms, however, are rarely found north of the Gulf states.

Lifecycle and Description

Adults: The melonworm moth has a brown head and white-tipped abdomen with bushy hair-like tufts. Their wings are white, slightly iridescent centrally and are edged with a broad band of dark brown. Wingspan of the melonworm moth is about an inch. Melonworm moths are active in the night.

Eggs: Melonworm moths deposit oval, flattened eggs in small clusters of about 2-6 eggs. Eggs are generally deposited on buds, stems, and underside of leaves of host plant. Initially they are white or green but gradually turn yellow. Eggs hatch in 3-4 days.

Larvae: Newly hatched melonworm larvae lack color, but turn pale yellow-green colored in a few days. Melonworm larvae build silk or cocoon-like nests under leaves where they rest or hide in during the day while continuing to feed on foliage. Mature melonworm larvae are dark green with 2 lateral white stripes that are their most distinctive characteristic. The stripes fade or disappear prior to pupation.

Melonworm larva

Melonworm larva.

Pupae: Prior to pupation, larvae spin a loose cocoon on the host plant, often folding a section of the leaf for added shelter. Pupa is light to dark brown color, measures about 15 mm in length and lasts about 9-10 days.

A melonworm can complete its life cycle in 30 days and there can be up to 4 generations a year.

Host plants

Melonworms are restricted to feeding on cucurbits; both wild and cultivated species may be attacked. They prefer feeding on summer squash and winter squash. Pumpkin is of variable quality as a host, while cucumbers, gherkins and cantaloupes are attacked, but not preferred. Watermelon is a rare host.

Damage

Melonworm damage is mainly on foliage, especially if foliage of preferred host is available. Usually the leaf veins are left intact, resulting in a lace-like appearance. If foliage is exhausted, or if the plant is a less favored species, the larvae may feed on the surface of the fruit or even burrow into the fruit. Hence melonworm larvae are popularly called ‘rindworms’ among growers because they cause scars on the surface of melons.

Melonworm damage to foliage.

Melonworm damage to foliage.

Organic Control and Prevention of Melonworms

1. Early planting: Early-planting enables growers to harvest most of the crop before the melonworm can cause excessive losses. Very early spring plantings are seldom damaged.

2. Trap crop: Squash could be used as a trap crop to keep pickleworm from attacking other cucurbits, as squash is the preferred host of melonworms.

3. Screen covers: The use of floating row covers has been shown to be effective against melonworm moths and other insects from laying eggs on the plants. Row covers should be applied immediately after planting; however, they must be removed when plants begin to flower to allow for pollination.

4. Sanitation and weed control: Removal and destruction of infested plants including vines and fruit following harvest is a good cultural practice to reduce populations. Keeping the surroundings clean and weed-free can go a long way in preventing pickleworms from overwintering in and around your garden.

5. Fruit bagging: Although melonworms rarely bore into fruit, protecting fruit with a layer of paper bag or plastic will definitely help.

6. Monitor and handpick: Scout regularly for eggs and larvae among your cucurbits. Melonworm larvae feed mainly on foliage and can be easily spotted underneath leaves nestling in their silken cocoons.

7. Natural predators: Melonworms have natural enemies such as the soldier beetle, Calosoma beetles, Harpalus beetles, red imported fire ant, trichogramma wasps and braconid wasps that can help control or prevent infestations to an extent.

8. Spraying Bt (Bacillus thuringiensis) or Steinernema carpocapsae, a beneficial nematode is a great solution according to a vegetable crop specialist at the University of Florida. To control an infestation, spray Bt or beneficial nematodes in the early evening on susceptible plants.

9. Neem and Spinosad: Neem products are botanical insecticides that are effective against a variety of insect pests including pickleworms through contact toxicity, disruption of insect molting and feeding deterrence. Spinosad is derived by microbial fermentation and is effective against melonworms while being safe to most beneficial insects.

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