Biological control of fruit piercing moth in the South Pacific

• Ministry of Agriculture, Forests, Fisheries and Meteorology, Samoa
• Department of Resources and Development, Federated States of Micronesia
• Ministry of Agriculture, Fisheries and Forests, Fiji
• Ministry of Agriculture and Forestry, Tonga
• Ministry of Agriculture, Cook Islands

Fruit-piercing moths (FPM) have been recorded as attacking over 40 fruits worldwide. They are serious pests of most tropical and subtropical fruit in the Pacific region. Citrus varieties, mango, papaya, lychee, stone fruit, carambola and kiwi fruit as well as capsicum and tomatoes are all particularly susceptible. In Australia five species of the moth are pests (Othreis fullonia, O. materna, O. jordani, Khadira aurantiaca and Eudocima salaminia) but in the Pacific O. fullonia is the major pest. Moths (males and females) attack both unripe and ripe fruits but most damage is caused at the ripening stage by puncturing the fruit and sucking the juice. Rots quickly enter and destroy the whole fruit. Single moths can cause severe damage whilst several moths can devastate a whole crop.

In Samoa the problem of FPM is so severe that no commercial citrus fruits can be grown. Citrus fruit that appears in the markets is usually grown in domestic gardens where intensive methods, such as applying bags to the fruit, are possible. The only monoculture of citrus grown in the country is a government-owned orchard on the island of Savaii. In Fiji all five of the most important fruits grown (citrus, pineapple, papaya, mango, and passionfruit) are attacked by FPM. Particularly large losses of citrus fruit occur with up to 15% loss of fruit at the largest citrus orchard on the island of Viti Levu where the value of fruit damaged has exceeded F$200 000 per year. On Tonga serious damage to tomatoes and capsicums has prevented the export of these crops. Several other fruits are also affected although outbreaks of the moth are more seasonal than in the other countries. Enormous yearly losses have also been estimated for Australian horticulture due to FPM attack and crop losses to individual farmers range up to 100% in some cases. The total loss estimated in 1989 for only 41 properties across Australia was $140 797.

This project replaces ACIAR project 8802 in which biological control of the moth was attempted in Samoa and two egg parasites from Papua New Guinea (where FPM is not a problem to fruit growers) were released. The first parasite, Telenomus sp., established after its release in 1988 and within 6 months began to reduce the levels of egg hatching. However, the second parasite released, Ooencyrtus sp., did not establish successfully which may have been due to competition from a native W. Samoan parasite, O. crassulus. In Fiji Ooencyrtus sp. was released and quickly established in all the islands.

The current project will continue the research of Project 8802 in all three Pacific countries. In Samoa the reasons for the failure for the introduced parasite species Ooencyrtus sp. to establish will be explored. In Tonga the both Ooencyrtus sp. and the native Samoan O. crassulus will be introduced and the interaction between these two parasites studied. In both Fiji and Tonga the second PNG parasite, Telenomus sp. will be introduced and its impact on the moth population will be assessed in conjunction with the previously introduced species and other indigenous species. In all three countries fruit losses to growers will be assessed. Researchers in each country will monitor the levels of fruit damage by regular counts of puncture holes on a standard number of fruit trees and assessment of fallen fruit for FPM attack.

In addition to the field trials described above, laboratory studies will also be carried out. Scientists in each country will study reproduction of the moth on Erythrina leaves (the host plant of the moth) and the reproductive potential of egg parasites under controlled conditions. In Tonga counts of adult moths are made once per week at the international airport which provides a good standardised measure of the adult moth populations.

Biological control of FPM will greatly increase the extent to which fruit can be grown in the Pacific countries of Samoa, Fiji and Tonga. Transfer of the expertise and management programs developed will also benefit several other Pacific nations with the same problem, including Australia.