Orchids are one of the most diverse – and beautiful – groups of flowering plants in the world, with more than 20,000 species classified. But with this beauty comes trouble, as their popularity has led to overharvesting of orchids. Combined with loss of habitat due to human expansion, over 70 percent of Japan’s native orchid species are currently classified as endangered by the Ministry of the Environment.
Now, a group of Japanese researchers has revealed an additional threat to orchid populations. There is a species of seed-eating fly that is causing critical damage to the seed production of numerous orchid species. The researchers report that if the damage caused by this fly is occurring across Japan – and keeps going at a fast rate – these already-endangered orchid species may be unable to reproduce.
The research team, led by Professor Kenji Suetsugu from Kobe University Graduate School of Science, conducted a survey to identify pollinators of orchid species. During this survey, they found that in pollinated fruit which should be viable to produce seeds, a seed-feeding fly (Japanagromyza tokunagai) was eating the seeds.
This fly lays its eggs in the young fruit of blooming orchids, so that when the insects begin to grow, they eat the seeds of the fruit. When the pupae eventually hatch into their winged forms, they make a hole in the fruit in order to escape. However, because the fruit that is parasitized by these flies eventually grows to be the same size as normal fruit, it appears to be healthy from the outside. This leads the researchers to believe that we have likely underestimated the damage caused by these flies. Furthermore, many of the fruits parasitized by the flies will produce no seeds at all.
For their study, the researchers artificially pollinated five species of orchids in Japan’s Kanto region, covering some specimens with bags to prevent any flies from entering. They then compared the quality and amount of seeds produced by each plant. Their results showed that in every single orchid species tested, damage caused by J. tokunagai reduced seed production by more than 95 percent.
Scientists believe that it is also possible the damage caused by these flies may be increasing in recent years. This could be because the flies are a non-native species that lives in areas with few natural enemies, as well as the fact that orchid populations have become fragmented.
“Going forward, we want to shed more light on the damage caused by J. tokunagai,” says Suetsugu. “We plan to do this by quantifying the damage in other areas of Japan, and by testing the theory that J. tokunagai is a non-native species through genetic analysis.”
Image Credit: Takuto Shitara