Study of economically important fruit flies in Malaysia and development of control methods

• Malaysian Agricultural Research and Development Institute, Malaysia

All countries in Southeast Asia suffer major economic losses from infestations of tropical fruit flies. In Malaysia, production in some fruit and vegetable crops is reduced by as much as 90% in uncontrolled situations, and as much as 50% where chemical control methods are employed. The continuing presence of fruit flies imposes limitations on exports, and prevents expansion of cropping in fruits such as starfruit, mandarin and pomelo, for which there is a considerable potential in local and export markets.
To bring about control of fruit fly, entomologists need precise information about the species which infest the entire range of fruits and vegetables in a region. Each species distinguished must be tested for response to various attractants such as male lures or protein hydrolysate bait spray, as different species respond differently.
Information about many pest species in Southeast Asia is scarce, due to the lack of adequate reference collections of economically important insects. Trained personnel are needed to study and identify local insect faunas. It is also important to determine level of damage inflicted by each species and its seasonal abundance, factors which may vary significantly throughout Malaysia.
The taxonomic situation is complicated, there being at least 200 species of the sub-family Dacinae in Southeast Asia. Many of these form closely related species complexes which are indistinguishable by normal comparison of external morphological characters.
In this project scientists from Australia and Malaysia will collect specimens of infested fruit, in all fruit-growing regions and in all seasons. Workers will then clarify the taxonomic identity and biological characteristics of the pest species of fruit fly in Malaysia. Experience on South Pacific fruit fly has shown that closely related species can vary in their behavioural patterns and host specificity, a significant factor in the use of attractant bait sprays. Where more than one species occurs in one host fruit, correct identification is essential to initiate preharvest control studies.
An accurate taxonomic assessment will benefit Australia as well as Malaysia. With its northern boundaries so close to Southeast Asia, Australian scientists need information on species which may reach Australia, so that appropriate control measures can be quickly implemented should an outbreak occur. Malaysia must know the identities of all important species and their commercial hosts before the disinfestation procedures required for the export trade can be adequately executed.
Extensive collection of host plants and fruit flies will be carried out, based on areas of major production and peak fruiting seasons. Host plants will be identified, in Malaysia where possible, and all relevant fruit fly specimens will be studied at the Entomology Branch of the Department of Primary Industries, Brisbane. The taxonomy of the various species complexes will be finalised by scanning electron microscopy.
Establishment of a collection of economic fruit fly species is planned for at least one institution in Malaysia and representative material will be lodged in the Australian National Insect Collection in Canberra.
Field and laboratory trials in crop hygiene, bait spraying and insecticide spraying will aim to establish the best methods for preharvest treatment of each economically important species of fruit fly, with particular reference to the cost for household, village and semi-commercial/commercial orchards.