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Photo: Fruit fly on male Gurania spinulosa Cogn flower.
While fruit flies and plant diversity have co-evolved in the neotropics, new research shows geography and other factors also play an important role in generating insect diversity. Photo courtesy of Marty Condon, Cornell College.

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Fruit Fly Diversity Is in the Details

By Ann Perry
May 16, 2008

Many scientists attribute the diversity of plant-feeding insects to plant diversity and to the many ways insects can survive on host plants. An article published this week in Science explores how these niches are used by one group of insects—and also examines evidence that using niche diversity alone to estimate species diversity can result in an undercount. The authors conclude that for this insect group, diversity is greater than the sum of plant parts.

Molecular biologist Sonja Scheffer, in the Agricultural Research Service (ARS) Systematic Entomology Laboratory in Beltsville, Md., teamed up with three colleagues to study the ecological links between tropical fruit flies in the Blepharoneura genus and their host plants. The other researchers were Marty Condon, a biology professor at Cornell College in Mount Vernon, Iowa; ARS support scientist Matthew Lewis, and Susan Swenson, a biology professor at New York’s Ithaca College.

Blepharoneura fly larvae feed within the flowers or fruits of plants in the cucumber family. For their study, the researchers collected and raised 2,857 different Blepharoneura specimens from 24 neotropical host plant species. DNA analysis indicated there were at least 52 distinct species in the collection.

The researchers found that only one of the fruit fly species they raised ate two kinds of plant parts—seeds and flowers. All the others ate only one or the other, and many of the flower-eaters were so specialized that they ate only male or only female flowers.

Most of the fly species were associated with only one host plant species. On the other hand, many of the plants hosted a range of species. One plant species supported at least 13 species of the fruit flies.

Location also played a role in the findings. Some of the fly species were geographically widespread. But others could only be found within a limited geographic range, even though the range of the host plant was much more extensive.

The team concluded that host plant and niche diversity plays a significant role in the extraordinary diversity of Blepharoneura flies. But geographical factors—and the passage of time—may play an even greater role.

ARS is the U.S. Department of Agriculture's chief scientific research agency.