The origin and distribution of a little yellow fly is solved after 90 years.

A species that was discovered living in Eucalyptus flowers in Sydney a century ago might be assumed to be an Australian endemic. But in 1983 I identified this species in southern Africa and Madagascar on plantation eucalypts. Was this little fly following the spread of Eucalyptus around the world? In 1987 I predicted that the fly would be found anywhere that Eucalyptus was grown. It turned up in Los Angeles in 2013. But there’s a hitch: I had also discovered this fly in the blossom of Syzygium and Syzygium is by no means restricted to Australia.

In December 1923 some small yellow flies were collected from unspecified flowers in the Sydney suburb Como. The specimens were, together with many other nameless fly species, sent to the leading fly taxonomist of the day—John Malloch, at the United States National Science Museum. In 1924 the species was named Drosophila flavohirta by Malloch because of its distinctive yellow hairs (thus flavo hirta) specimens were then returned to the Australian Museum.

Half a century passed before the fly was reported again. In 1975 at La Trobe University, the taxonomist Ian Bock gathered all major collections of Australian Drosophila species to begin his detailed study of the genus in Australia. Among this material were some unidentified yellow flies that matched the Como type specimens. Furthermore, the label-data on these specimens indicated an association with Eucalyptus blossom.

In 1982, after several years as Bock’s student, I began research in Johannesburg on the genus Drosophila in southern Africa and Madagascar and was almost immediately prevailed upon to identify a “local” species that was impacting very negatively on honey-yield in Eucalyptus plantations. I recognized the species as Drosophila flavohirta, and it seemed that the species, which was so well-adapted to life in Eucalyptus flowers, had followed the plant to Africa from Australia. Its rarity in Australia seemed to be consequent upon the presence of natural predators and parasites, its abundance in South Africa seemed to be the result of their absence. This view seemed so self-evident that it was never really tested.

In 1987 in Madagascar I discovered Drosophila flavohirta not just on Eucalyptus but also on Syzygium blossom. This led me to conclude two things (a) that the species might actually occur in many countries where Eucalyptus is now grown like North America and the Mediterranean, and (b) the species may have originated outside Australia.

This new evidence meant that the fly-flower association was not limited to just the one genus Eucalyptus in the family Myrtaceae but that myrtaceous flowers of many genera apparently provided suitable habitat. Since Myrtaceae is by no means restricted to Australia this new discovery undermined the earlier theory that the species had evolved in Australia and spread.

Another few decades passed and in 2014 Drosophila biologists at an international fly conference in Potsdam approached me because they had discovered a very strange “new”, and distinctly yellow, species of Drosophila in urban Los Angeles. Because Drosophila is such an important model organism in genetics and also because California had a long history of genetics research the discovery was all the more exciting because this “new” yellow species of Drosophila was genetically very similar to the famous Drosophila melanogaster. I determined the species in question to be Drosophila flavohirta.

With John Tann in December 2014 I revisited Como and discovered Angophora costata, and nothing else, in full bloom everywhere as it had probably been in 1923, it was not difficult to collect more specimens of D. flavohirta, and so the first specimens were almost certainly taken from Angophora blossom. The myrtaceous genera with suitable blossom for this species now include Eucalyptus, Syzygium, Angophora and Callistemon.

The importance of knowing that inconspicuous little insects often have unexpected value in understanding how our natural world interconnects cannot be over emphasized. Small animals of great importance can live right under our noses yet unless we focus thoughtfully on the apparently insignificant we see nothing.

Dr Shane McEvey
Editor, Records of the Australian Museum
Entomologist, Australian Museum Research Institute

More information:

Grimaldi, D.A., Ginsberg, P.S., Thayer, L., McEvey, S.F., Hauser, M., Turelli, M., & Brown, B.V.. 2015. Strange little flies in the big city: exotic flower-breeding Drosophilidae (Diptera) in urban Los Angeles. PLoS ONE 10(4): e0122575.