Evolution May Be To Blame for Pest That Plagues Apple Trees

Evolution may be to blame for a certain agricultural pest that began plaguing apple growers in the 1850s. Scientists have found that extensive, genome-wide changes that occurred in a single generation may have caused the spread of this particular pest.

In this latest study, the researchers looked at the fruit fly Rhagoletis pomonella, also known as the "apple maggot." This native of North America lays its eggs inside the fruit of the hawthorn tree. Yet in the 1850s, a splinter group of this insect began laying its eggs in apples in upstate New York.

"Today, there are two forms of Rhagoletis pomonella in the U.S., the ancestral form that times its life cycle to the hawthorn tree and a derived form that is timed to apple trees, which fruit about 3 to 4 weeks earlier," said Scott Egan, the lead author of the new study, in a news release. "These two forms have evolved very distinct differences and are on the path to evolving into two new species, and because they have a single generation per year, we know that all of the differences between the two has happened in no more than 170 generations."

In this latest study, the researchers conducted an extensive genetic analysis of the species. They also collected flies from native hawthorn trees, divided them into two groups and raised the flies under haw- and apple-like conditions. They then measured the differences between the groups.

"For the ancestral flies that had been raised for one generation on the apple cycle, we documented changes in more than 32,000 SNPs," said Egan. "Overall, we found that the genetic changes undergone by this first generation accounted for up to 70 percent of all the genetic changes that had occurred between the two populations since the 1850s."

The findings reveal that these changes occurred rapidly, and show a bit more about how evolution occurred in these flies. This underscores the importance of ecological selection at early stages of divergence.

The findings are published in the journal Ecology Letters.

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