As pollinator populations decline, fly flies can offer Great Britain

Billions of hoverflies from Europe descend each spring in the south of Britain. The black and yellow striped bugs are no more than half an inch long but make the long trip to Britain for the summer.

Once arrived, hoverflies pollinate the flowers and lay their eggs. Researchers have found in a new study that fly populations have remained stable, unlike honey bees and other insects. The discovery suggests that insects may become increasingly important for crop pollination.

"They are widely regarded as the second most important pollinators, after bees," said Karl Wotton, an evolution biologist at Exeter University in the UK, who led the new search.

Mass migration

Wotton and his colleagues tracked migration errors with radar equipment for 10 years. The radar covered about 27,000 square miles of southern Britain, a region a little smaller than the state of South Carolina. To ensure that they followed only the hoverflies, the researchers then filtered the data to match the size and shape of the hoverflies. Overall, the team monitored more than 600 hoverfly mass migrations.

The researchers found that flies appear for the first time in May and become more abundant as the summer progresses. Females lay up to 400 eggs so larvae abound in July. The flies begin the journey to the European continent in August. In September, the numbers fell again.

The researchers estimate that the larvae that brood throughout the summer increase the number of hoverflies by four. In total, more than 2.5 billion hoverflies travel to and from southern Great Britain each year, the team reports in the newspaper Thursday. Current biology.

"The number of migratory hoverflies that come and go over Britain was much higher than expected," said Wotton. And their number has a huge impact on British cultures.

Pollination prowess

The hoverfly larvae feed on aphids, the main crop pests in Europe, explains Wotton. Every summer, one to two generations of larvae hatch. Hungry baby bugs eat aphids at maturity. According to the researchers, they probably consume more than a million aphids of cereals per hectare of arable land. This means that hoverfly larvae clean about 20% of the typical population density of spring aphids.

Flying flies also provide essential pollination services to wildflowers, berries and agricultural crops belonging to the mustard family, such as broccoli, cabbage and rapeseed, a plant that produces canola oil. . And they are very good at that. Hoverflies frequently visit the flowers and their numbers are equivalent to the managed honeybee populations on which agriculture currently rests.

Insect populations are in trouble around the world. But hoverflies and other migrating insects appear to be somewhat resilient. During the 10-year study period, the number of hoverflies remained relatively constant.

"Migratory insects generally go against the declining trend that we are seeing with many other insects," said Jason Chapman, ecologist at Exeter University, who had directed the 39, study with Wotton, in the press release. "Their mobility is probably a key element because it allows them to go from the front to find the best habitats."

"Given the fact that many beneficial insects are declining, our results show that migratory hoverflies are essential to maintaining essential ecosystem services," he added.