Drosophila flies prefer to lay their eggs in untouched fruit

An invasive fly from Asia that is known for attacking fruit crops is very particular about where it chooses to lay its eggs. The spotted wing drosophila fly, D. suzukii, prefers to lay its eggs in places that have not been visited by other flies, according to a new study from North Carolina State University.

The discovery raises new questions about how the flies can tell which pieces of fruit are untarnished, and about what this could mean for pest control.

Although Drosophila suzukii is native to east Asia, the fruit fly has spread rapidly across Africa, Europe, and both North and South America over the past 10 to 15 years. 

These invasive flies lay their eggs in ripe fruit, which poses problems for farmers.

“Ultimately, we’re talking about hundreds of millions of dollars in potential crop losses and increases in pest-management costs each year in the United States,” said study co-author Professor Hannah Burrack. “These costs have driven some small growers out of business.

“The first step toward addressing an invasive pest species is understanding it. And two fundamental questions that we had are: Which plants will this species attack? And why does it pick those plants?”

While observing Drosophila invasions on farms, the experts noticed that the flies’ egg-laying behavior varied according to the size of the infestation. If they were part of a smaller population, the flies laid only a few eggs in each piece of fruit, and only when the fruit was ripe. 

On the other hand, if the flies were part of a large population, more eggs were laid in each piece of fruit. To investigate, the researchers conducted a series of experiments. 

The surprising results revealed that, when given a choice, D. suzukii preferred to lay its eggs in fruit that other flies had never visited.

“It doesn’t matter if the other flies lay eggs,” said Professor Burrack. “It doesn’t even matter if the other flies are male or female. It only matters if other flies have touched a piece of fruit. If untouched fruit is available, D. suzukii will reject fruit that other flies have visited.”

“We’re not sure if the flies leave behind a chemical or bacterial marker, or something else entirely – but the flies can tell where other flies have been.”

The researchers said that the next step is to determine what, exactly, the Drosophila suzukii flies are detecting as they scope out the fruit.

“If we can get a better understanding of what drives the behavior of this species, that could inform the development of new pest-control techniques,” said Professor Burrack. “We’re not making any promises, but this is a significant crop pest – and the more we know, the better.”

The study is published in the journal Scientific Reports.

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By Chrissy Sexton, Earth.com Staff Writer