Photo 2. Severe damage on cucumber by Diaphania indica. The caterpillar has emerged from the rolled edges of the leaf and skeletonised the leaf by eating between the veins.
Photo 3. Caterpillar of Diaphania indica showing the characteristic double white lines along its back.
Cucumber moth. Other common names are, melon moth, pumpkin caterpillar, cucurbit caterpillar and watermelon worm.
Diaphania indica. A moth of the Crambidae.
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.
Cucurbits; common cucurbits are watermelon, cucumber, melon, pumpkin and snake gourd.
The caterpillars do the damage. After hatching, they roll the leaves with silken threads and eat the leaves between the veins (Photos 1&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. On occasions wasps parasitoid wasps hatch from them (Photo 5).
The adult is very obvious (Photo 6). 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.
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.
Look at the young leaves: look for leaves where the veins are still present, but the parts between have been eaten. Inspect the young fruits: look for signs of caterpillar damage. Look for caterpillar faeces or droppings.
Tiny wasps that are hard to see with the naked eye attack the caterpillars (Photo 5), and lacewing larvae eat the young caterpillars (Photo 6).
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.
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 is best used for sucking insects as it has systemic activity, meaning it enters the plant and moves inside it. It will kill the caterpillars, but it will kill other insects, too, whether they are pests or beneficials.
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/).
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.
This fact sheet is a part of the app Pacific Pests and Pathogens
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