Tiny traces of DNA can help researchers track trends over time, such as population declines and the types of insects that interacted with the plants before harvesting and packaging, according to a recent study published in Biology Letters.
That could include bees that pollinated the plants, caterpillars that built cocoons on them, and spiders that spun webs around them.
“There’s very, very specific interactions and very cryptic interactions of which we know very little because no one has basically put in the effort of studying this before,” Henrik Krehenwinkel, the lead study author and an ecological geneticist at Trier University in Germany, told the Smithsonian Magazine.
Krehenwinkel and colleagues found that dried plant material is a promising source for environmental DNA analysis, which has become a popular research method in the biomonitoring field in recent years. Researchers have used water, soil, and plant surfaces for samples. For this study, the researchers chose teas and herbs because the leaves are typically crushed and dried, which allows for the possibility of DNA traces.
“In a sample like coffee, which is very heavily processed, you probably have very little DNA left,” Krehenwinkel said. “So we tried things which were kind of as natural as possible.”
The research team bought teas and herbs at local grocery stores that came from four continents, he told the magazine. They bought multiple versions of the same product from different brands to test a wide range of origins.
Then the team developed a method to extract and amplify the arthropod DNA from the plant materials. Most of the DNA in tea leaves is from the tea plant, but a small amount can be traced to insects.
“Probably 99.999, or something like this, percent of the DNA we extract is plant DNA, and only a tiny fraction, which is left, is the insect DNA,” Krehenwinkel said. “Which, of course, is good for the tea drinkers because they want to drink the tea and not the insects.”
The research team analyzed various commercially produced teas and herbs such as chamomile, mint, and parsley. The samples contained traces of DNA for a wide range of insect communities, totaling more than 1,200 different species in more than 20 orders. On average, they found more than 200 different types of arthropods in each tea sample.
In general, the species matched the known distributions for the plants and arthropods. For instance, mint tea contained DNA from insects found in the peppermint-growing region in the Pacific Northwest, and green tea contained DNA from insects native to East Asia.
The testing method could be applied to any dried plants, the researchers wrote, which could make it a valuable tool for monitoring endangered insect species and tracking crop pests.
Krehenwinkel is also interested in extracting insect DNA from dried plants that were collected decades ago and stored in museum collections, which could be compared to modern plants to track how species have changed, the magazine reported. This could potentially help with insect conservation efforts as well.
The new method could allow researchers to “travel back in time and understand how communities have changed,” he said.