Identification and control of pest fruit flies of the South Pacific

• Ministry of Agriculture, Forests, Fisheries and Meteorology, Samoa
• Ministry of Agriculture, Fisheries and Forests, Fiji
• Ministry of Agriculture, Cook Islands
• Ministry of Agriculture and Forestry, Tonga

Fruit and vegetables, a significant component of the diet of people of Pacific nations, are also becoming increasingly important for generating export income. Although exports are not large by world standards, their value in terms of balance of payments is great. Most fruit exports have been to New Zealand, Australia and Japan - countries that regard fruit flies as a major threat - and disinfestation to meet the quarantine requirements of these countries has been achieved by ethylene dibromide (EDB) fumigation. However, permitted residue levels of EDB in produce are about to be reduced to levels that are incompatible with fruit fly disinfestation.

Research to find a suitable heat-treatment method to replace EDB fumigation is in progress (ACIAR project no. 9051). Preharvest control treatment is also required to keep the pests to the lowest possible levels before disinfestation is applied. This in turn requires detailed biological information on each fruit fly species.

The project is based on an earlier ACIAR-supported project (no. 8343) on fruit flies of Malaysia, which provided information on taxonomy, wild and commercial fruit hosts, levels of infestation, and geographic distribution and seasonal abundance of species. It also developed a cheap and effective field control system using protein bait sprays. An external review of the project recommended that similar work be extended to other areas.

The present project was set up to provide comparable information and assistance for Cook Islands, Fiji, Tonga and Samoa. It will be run in conjunction with a complementary project being conducted by the South Pacific Commission (SPC), and will undertake:

. systematic collection in all seasons of cultivated and wild fruits, and rearing of fruit flies and fly parasites gathered from these, to determine the geographical distribution, host fruit range, pest status (including maximum infestation levels), seasonality, and extent of control by natural enemies for each fruit fly species; and
. development of cheap and locally available protein bait materials that can be used in large-scale field control of the flies by protein bait spraying.

The project will involve two main fields of investigation - host fruit studies, and field control trials using protein bait sprays. The first component will be undertaken collaboratively by ACIAR, SPC and local workers in each country. Experimental procedures will involve sampling of commercial and wild fruits in each distinct region of each country and holding them in the laboratory for fruit fly and parasite emergence. When they emerge from pupae, adult fruit flies will be fed until they develop full colouration and then killed and sent to Dr Drew at the Queensland Department of Primary Industries (QDPI) in Brisbane for identification. The identity of parasites and relevant biological data will be collated by Dr Walter at the Department of Entomology, University of Queensland.

In the second component, the team will seek cheap, locally available sources of protein, especially yeast by-products from Pacific breweries, that may be useful (after modification if necessary) as baits for fruit flies. QDPI will modify candidate protein sources and test their attractiveness for fruit flies in the laboratory in Brisbane. The SPC project will then test these protein baits in semi-commercial field trials in the Pacific Islands.

The project is expected to bring benefits to all levels of the Pacific communities, including:

. increased production of fruit and vegetables, leading to greater and cheaper availability of these healthy foods on domestic markets, and increased prospects for fruit exports;
. acquisition of biological data that will provide a basis for developing effective postharvest disinfestation procedures for quarantine purposes;
. less exposure to insecticides for growers and consumers; and
. technology transfer of research methodology relevant to gaining practical familiarity with fruit flies

Australia will benefit from a more extensive knowledge of Pacific fruit fly pests that threaten the country, and by increased experience in fruit fly control techniques in a variety of tropical and subtropical fruit crops now being introduced for expansion of tropical horticulture production.