A groundbreaking new technique for studying lake sediments can tell scientists more about the frequency and intensity of past and future insect epidemics, their impact on the forest environment and how they are linked to climate change.
“This is an exciting discovery, which will greatly increase our knowledge of prehistoric forest ecosystems,” said Dr. Miguel Montoro Girona, a researcher at the Swedish University of Agricultural Sciences in Umeå, Sweden.
“It is comparable to the fossil pollen and charcoal markers in sediments, which revolutionized prehistoric research to provide information on plants, climate and forest fires going back thousands of years. Our new method can be applied to many ecosystems where moths and butterflies have a marked influence on the landscape.”
Moths are one of the most widespread and recognizable insects in the world.
In the boreal forests of North America, which are mainly comprised of coniferous, evergreen trees, the larva of one moth species — the spruce budworm (Choristoneura fumiferana) — can periodically cause severe and widespread damage. This leads to millions of dollars of lost revenue to the forest-based economy.
It was during a routine observation of one of these outbreaks that Dr. Montoro Girona and co-authors had a Eureka! moment.
“Together with an insect specialist, we recently identified a ‘strange’ structure in a colleague’s lake-water sample, which turned out to be a scale from a moth wing,” said Dr. Hubert Morin, a researcher at the Québec University, Canada.
“Afterwards, during a spruce budworm outbreak, I noticed the lakes were covered in dead moths. Knowing they are made from a material that is likely to be well-preserved in the sediments of lakes, I realized they had the potential to provide information about these swarms going back thousands of years.”
This hunch turned out to be true. Taking a 5-m-long core of sediment from a forest lake near Québec, which represented 10,000 years’ worth of sediment deposit, the team spent five years perfecting their method of extracting, examining and counting moth scales under the microscope from each sediment layer.
“Our analysis revealed peaks of moth scales that corresponded to known periods of insect outbreak,” said Dr. Lionel Navarro, also from the Québec University.
“This means we can work out when these epidemics occurred before records began.”
“This new method will be of enormous help to future research in areas as wide as ecology and evolution, biodiversity conservation, climate change and forestry.”
The findings were published in the journal Frontiers in Ecology and Evolution.
Miguel Montoro Girona et al. A Secret Hidden in the Sediments: Lepidoptera Scales. Front. Ecol. Evol, published online January 26, 2018; doi: 10.3389/fevo.2018.00002