Photo 2. Stem of bele split open to show a caterpillar of Earias vittella, and the frass that it pushes out through the entrance hole.
Bele shoot borer, spotted bollworm, spiny bollworm
Worldwide. Asia, Africa, Oceania. It is recorded from Australia, Fiji, Guam, Federated States of Micronesia, Northern Mariana Islands, Palau, Papua New Guinea, Samoa, Solomon Islands, Tonga, and Vanuatu.
The caterpillar attacks bele (aibika, sliperi kabis, island cabbage, Abelmoschus manihot), okra, hibiscus, and tomato.
Caterpillars do the damage by feeding inside the stems (Photos 1-3). The tips and leaves wilt and die (Photos 4&5). Caterpillars also feed inside fruits and pods of cotton and okra. Adult moths lay eggs at night, singly, on shoots, buds and young fruit.
Eggs are light blue-green, round, and about 0.5 mm across. They gradually change to brown just before hatching; they hatch into caterpillars in the early morning, after 3-7 days. The caterpillars may move some distance before boring into the soft growing parts of the plant to feed (Photo 6). They are grey-brown with orange spots and a black head. The body is up to 18 mm long and 3 mm wide, with two pairs of fleshy bumps on each body segment. They are full-grown after 9-17 days.
Mature caterpillars spin a silken cocoon, which is brown, felt-like, and shaped like an upside-down boat. Cocoons are fastened to the plant, to debris on the ground, or within cracks up to 30 cm deep in the soil. Inside the cocoon, the caterpillar turns into a pupa that is about 13 mm long, with three small spikes on its tail. The pupa lasts for 1-2 weeks, before it splits open and an adult moth emerges.
Adults live for up to 1 month, feed on nectar, and lay up to 500 eggs. Adults are 12 mm long, with a wingspan of about 20 mm (Photo 7). They are mostly white, with a central green wedge pattern running along their front wings.
In Fiji, there are reports of the shoot borer destroying about 20% of the okra crop, and in India it is a major pest of cotton bolls. In Solomon Islands, it is the most common concern of farmers attending plant health clinics.
Look at the stem tips and leaves to see if they are wilting and dying. Look closely for small holes in the stem below the dying tip. The caterpillars push their waste (frass) out of these holes, and this is often very noticeable (Photo 5). Break the stem near this hole to find the caterpillar in its tunnel.
Small wasps attack the eggs, caterpillars and pupae, and lacewings and ladybird beetles eat the eggs. It is important to think about these natural enemies when considering how to control Earias. If insecticides are used, choose ones that do not kill these beneficial insects. Preferably, use those that are allowed under organic vegetable production.
Populations of Earias tend to build up slowly, so only two or three applications of pesticide may be needed to reduce numbers in a crop.
AUTHORS Grahame Jackson, Mani Mua & Helen Tsatsia
Photos 4&5 Graham Teakle, Canberra.
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
The mobile application is available from the Google Play Store and Apple iTunes.