Distribution. Oriental fruit fly occurs in tropical regions of Asia, including some Pacific islands. It became established in Hawaii about 1946. On occasion, oriental fruit fly appeared in California and Florida, but always was successfully eradicated. The environment in southern California, Texas, and Florida probably would be suitable for this pest, so it remains a threat. The taxonomy of this insect is uncertain; there likely are several species within the oriental fruit fly "complex." Thus, many elements of the life history, including host records, are suspect until confirmed.
Host Plants. Over 120 plants have been reported to serve as hosts of oriental fruit fly larvae, though many are attacked only during population outbreak conditions. Principal hosts are fruits such as avocado, apple, mango, peach, pear, citrus, coffee, and especially guava. Oriental fruit fly is so highly attracted to guava, and so effective at utilizing this host, that it has displaced Mediterranean fruit fly, Ceratitis capitata (Weidemann) as the principal pest of guava, and significantly lowered the overall density of Mediterranean fruit fly in Hawaii. Among vegetables, pepper, tomato, and watermelon are reportedly attacked.
The adult flies feed on secretions of extrafloral nectaries, honeydew, rotting fruit, bird dung, and other liquefied items. The adults survive only three days without water, and six days with water, but no sources of carbohydrate. The ability of flies to disperse long distances to obtain food is present in this species. However, unlike the clearly defined dispersal of melon fly, Bactrocera curcurbitae (Coquillett), between adult feeding and oviposition sites, it is uncertain how often oriental fruit flies relocate.
Natural Enemies. In the absence of natural enemies, which was the situation in Hawaii immediately after introduction of the fly, very high pest densities are attained. Searches were conducted in many countries for beneficial insects, and a predatory rove beetle (Coleoptera: Staphylinidae) and several hymenopter-ous parasitoids attacking the egg and larval stages were introduced. Apparently some of the wasps contributed materially to reducing population densities of this damaging fly, because fruit infestation levels declined by 1951 (Bess and Haramoto, 1961). The principal beneficial parasitoid is Biosteres arisanus (Sonan), but Diachasmimorpha longicaudata (Ashmead) and
Biosteres vandenboschi (Fullaway) (all Hymenoptera: Braconidae) also are considered important. Over a seven-year period on Oahu, Bess and Haramoto (1961) found that 68-79% of fly larvae in guava fruit were parasitized, though Vargas et al. (1993) reported only about 40-50% parasitism. Destruction of eggs by B. arisanus was sometimes considerable, up to 80%, probably owing to infection of eggs by bacteria and fungi following damage to the chorion by the parasi-toid (Bess et al., 1963). Rearing methods for B. arisanus have been developed (Harris and Okamoto, 1991). Parasitoid monitoring technology has also been studied (Stark et al., 1991; Vargas et al., 1991). Predation, especially by ants (Hymenoptera: Formicidae), was noted but not considered appreciable. Overall fruit fly densities were also determined significantly by availability of fruit and warm weather.
Life Cycle and Description. Oriental fruit fly can complete a generation in about 30 days. In tropical climates, many overlapping generations per year are reported. Fruit fly abundance typically coincides with availability of ripening fruit, though they tend to be most common in summer and autumn (Vargas et al., 1989; 1990).
Keys for distinguishing all life stages of these species were provided by Hardy (1949), White and Elson-Harris (1992), and Foote et al. (1993).
The adult flies sting fruit during the process of ovi-position. The presence of larvae is, of course, highly objectionable to consumers. Even if the larva fails to develop, fruit deformities may occur. Also, the ovipo-sition wound is frequently a site for invasion by bacterial and fungal diseases. Other insects such as fruit flies (Hymenoptera: Drosophilidae) and sap beetles (Coleoptera: Nitidulidae) may attack fruit infested by larvae. As many locations lack Oriental fruit fly, quar-
antine restrictions are frequently imposed that restrict the sale and transport of valuable produce.
Cultural Practices. Fruit can be protected from flies by being wrapped in netting or bags, as is sometimes done for melon fly. Obviously this approach is limited to small-scale fruit or vegetable production.
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