Problem Statement: Fruit flies, family Tephritidae, are one of the most economically important pests of fruit crops in the tropics. Subtle variations in morphology and feeding behaviour also make them one of the most commonly misidentified groups of organisms in the biological sciences. There are approximately 4,500 species occurring worldwide, primarily in tropical to sub-tropical forests where they feed and oviposit on the fruits of native and introduced plants. The majority of fruit flies pose minimal risk to cultivated fruits but those that do often cause serious damage and require costly management practices to limit their impact. As a result, there is always concern from government and industry when a potentially exotic ‘dorsalis-like’ fruit fly is detected in areas where the pest is not yet known to occur.

Methods: The most economically important group of fruit flies in South East Asia, the Pacific and Australia are members of the ‘dorsalis’ complex. Originally the ‘dorsalis complex’ was believed to consist of only a few species of oriental fruit fly. However, taxonomic work has shown that the complex is comprised of at least 52 species. In fact, many earlier records of Bactrocera dorsalis from Southern India, Sri Lanka and South East Asia were based on misidentifications of what are now known to be other species. At least seven species of the ‘dorsalis’ complex are major pests of fruit crops and other plant communities in many areas throughout their native range in South East Asia and have invaded islands in the Pacific and parts of North and South America.

In 1974 flies collected on the Cape York Peninsula of Northern Australia were identified as B. frauenfeldi, a species known from Papua New Guinea as a pest of mangoes. The arrival of this species resulted in a series of detection traps being established along a lengthy stretch of coastline from Queensland to Western Australia; the threat of the pest arriving from the north was perceived to be very real. The trapping program specifically targeted the oriental fruit fly and the melon fly (B. cucurbitae).

A discovery in November 1975 of a fly identified as the oriental fruit fly from Melville Island off Darwin brought fears that there had been another invasion. However, this species, while a member of the ‘dorsalis’ complex, was not found in commercial fruits. After isozyme, cytological and host plant studies it was found that the fly was not the oriental fruit fly but an indigenous species restricted to one local fruit, Opilia amentacea. The species found on Melville Island is endemic to northwestern Australia and has now been named B. opiliae.

Outcomes and impacts: The misidentification of the 'exotic' fruit fly and the subsequent response to identify and define the limits of the pest infestation in 1975-76 cost about A$1.6 million but saved the significant expense of an eradication programme, such as the A$35 million elimination of papaya fruit fly from Queensland in 1995-6.

Lessons: Deficient knowledge of the fruit flies of north Australia resulted in a false invasive pest alarm and unnecessary mitigation measures being implemented. The absence of rapid and accurate identification procedures prolonged the mitigation response and increased its cost. The availability of taxonomic expertise prevented further unnecessary measures being taken to control the falsely identified ‘exotic’ fruit fly.