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Cucumber moth (033) Print Fact Sheet

Common Name

Cucumber moth. Other common names are, melon moth, pumpkin caterpillar, cucurbit caterpillar, watermelon worm. In Southeast Asia, it is known as the white cucumber moth, with WCM as the acronym.

Scientific Name

Diaphania indica. A moth of the Crambidae.

Distribution

Worldwide. In the tropics and sub-tropics. Asia, Africa, North (Florida), South, theCaribbean, Europe, Oceania. It is recorded from American Samoa, Australia, Federated States of Micronesia, Fiji, French Polynesia, Guam,  Kiribati, Marshall Islands, Northern Mariana Islands, Palau, Papua New Guinea, Solomon Islands, Tonga, and Vanuatu.

Hosts

Cucurbits; common cucurbits are watermelon, cucumber, melon, pumpkin, snake gourd, and bitter gourd.

Symptoms & Life Cycle

The caterpillars do the damage. The small caterpillars (larvae) are often found in the expanding leaves of the new growth, and with those of medium size, feeding on the leaves between the veins (Photo 1). At a later stage, the larvae roll the leaves and feed from inside, and also pupate in the leaf rolls (Photo 2).

The eggs are oval, about 0.7 mm long and 0.4 mm wide, thin walled and whitish. They are laid in small groups on the growing parts of the shoot, usually on the underside of the leaves or on buds and flowers.

The eggs hatch and the caterpillars emerge. They are almost clear, but soon become green. Large caterpillars have two white lines along the back (Photo 3). When fully grown, they are about 20 mm long:

After a while, the caterpillars turn into pupae, green at first then brown (Photo 4). The pupae are in folds of the leaves. They are about 12 mm long and 3 mm wide. The adults hatch from the pupae after about 8-12 days.

The adult is very obvious (Photo 5). The wings are white with a wide brown border. When the wings are spread, they are about 25 mm wide. At the end of the body is a group of hairs, rather like a brush. The females wiggle this brush, possibly to send out a chemical to attract the males. The life cycle from egg to adult is about 25 days.

Impact

A serious pest. Apart from attacking the leaves, the caterpillars attack the flowers and reduce the number of fruits set. Young fruits are also attacked: the caterpillars damage the skin and cause the fruits to rot. Late stage caterpillars cause serious damage to bitter gourd by eating the soft-skinned fruit.

Detection & inspection

Look for small and medium sized caterpillars on the growing tips, new leaves and the underside of larger leaves. Look for fresh leaf chewing and fresh frass (droppings). Note, it is difficult to see the small caterpillars because they are the same colour as the leaves.

Management

NATURAL ENEMIES
All the common foliage dwelling predators will feed on the exposed caterpillars, for instance, lacewings, ladybird beetle adults and their larvae, and hoverfly larva (Photos 6-9). Different species of small parasitic wasps attack the eggs, caterpillars and pupae (Photo 10).

It is important to think about these natural enemies when considering how to control Diaphania. If chemicals are used, it is best to choose those that do not kill natural enemies. Preferably, use chemicals that are allowed under organic vegetable production.

CULTURAL CONTROL

Before planting:

During growth:

After harvest:

CHEMICAL CONTROL
Acephate (Orthene) is being used by many farmers for the control of this caterpillar in some Pacific island countries, but it is not the best choice. Acephate will kill all insects, whether they are pests or beneficial.

The following pesticides are recommended:


AUTHORS Grahame Jackson, Mani Mua & Helen Tsatsia
Photo 3 Wilco Liebregts, Ecoconsult, Fiji. Photos 4&5 Gerald McCormack, Cook Islands Biodiversity & Natural Heritage: (http://cookislands.bishopmuseum.org/). Photo 7 Whitney Cranshaw, Bugwood.org. Photo 8 Suzanne Neave, CABI, UK.

Produced with support from the Australian Centre for International Agricultural Research under project PC/2010/090: Strengthening integrated crop management research in the Pacific Islands in support of sustainable intensification of high-value crop production, implemented by the University of Queensland and the Secretariat of the Pacific Community.



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