Photo 1. Scabby areas on the skin of banana fruits due to the feeding of the scab moth, Nacoleia octasema.
Photo 2. Caterpillar of the banana scab moth, Nacoleia octasema, between banana fingers. In this case, the caterpillar is dark brown.
Banana scab moth
Nacoleia octasema (previously, Lamprosema octasema)
Narrow. Asia and Oceania. It is recorded from American Samoa, Australia, Fiji, Federated States of Micronesia, New Caledonia, Samoa, Solomon Islands, Tonga, Vanuatu, and Walllis and Futuna.
Banana, plantain, Heliconia and Pandanus.
The caterpillars feed on the skin of the young fruit, while hiding in protected areas between the fingers and the fruit stalk. Sometimes, they eat through the skin and feed on the banana pulp. Damaged areas form a black scab (Photo 1).
Eggs are laid in the early evening on or near to an emerging banana bunch. The eggs are flat, oval-shaped and about 1.3 mm across. They are laid singly or in clusters of up to 30 and look like overlapping fish scales.
The caterpillars hatch after about 4 days and move to the young fruit under the tightly closed bracts (the leaves around the young bunches) to feed. As the bracts and hands lift from the bunch stalk, the caterpillar moves to the next closed hand. When newly hatched, the caterpillars are about 1.5 mm long and clear yellow; when fully-grown, they are up to 50 mm long, and vary from pinkish-grey to very dark brown (Photos 2-4).
After feeding for about 2 weeks, the caterpillars are ready to pupate. They spin a thin silken cocoon, adding some rubbish, which helps to hide them. Inside the cocoons, the caterpillars turn into brown pupae. The cocoons are either on the banana plant or nearby in the leaf litter.
After 8-10 days, the adult moths emerge; they are a pale straw colour, with a wingspan of about 30 mm (Photos 5&6). They have a row of small black dots around the edges of the wings. Moths hide during the day; they mate and lay eggs in the early evening.
The scab moth caterpillar is considered a serious pest in Samoa and elsewhere in the southwest Pacific. It is also very damaging in the commercial plantations in Australia, and routine treatments are applied rather than relying on estimates of moth populations as they are difficult to predict. Any damage to the fruit can result in downgrading and/or rejection of the fruit and economic loss.
Look at the young developing fruit. Look for feeding damage - black scabs on the skin, or caterpillar droppings. Banana bunches should be inspected when bracts have begun to lift, but before they start to fall. Pay special attention to the undersides of the fingers - those closest to the bunch stalk.
The caterpillars are attacked by several kinds of tiny wasps that are hard to see without a microscope. Spiders and other general predators also attack them. These natural enemies, however, are not enough to reduce damage to acceptable levels.
Spraying with chemicals (rather than injecting them) often does not work against this pest, because the insect is so well hidden. Therefore, some commercial growers lift or remove the flower bracts and dust or spray insecticide onto the fruits after the flower has bent over. This method can stop some damage but not all.
AUTHORS Helen Tsatsia & Grahame Jackson
Photo 1 Nacoleia octasema caterpillar damaging banana "fingers" (Graham Teakle). Information (and Photos 2&4) Schmaedick M (2005) Banana scab moth. American Samoa Community College, Community & Natural Resources, Cooperative Research & Extension. Photos 3&6 Mani Mua SPC Sigatoka Research Station, Fiji. Photo 5 CSIRO website of Common Names. (http://www.ces.csiro.au/aicn/name_c/a_228.htm).
Produced with support from the Australian Centre for International Agricultural Research under project PC/2010/090: Strengtheni4g 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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