If the leaves of a tea bag could tell their stories, they would paint the picture of a thousand fleeting interactions. The bees have landed on it pollinating the flowers. The caterpillars chewed on them and built cocoons near them. Spiders attached webs to them.
But many relationships between plants and animals are undocumented. Cataloging every animal that feeds or pollinates a given plant can take a lot of time and effort. “There are very, very specific interactions, and very cryptic interactions that we know very little about because no one has made the effort to study this before,” says Henrik Krehenwinkelecological geneticist at the University of Trier.
But Krehenwinkel led a team of scientists who found a new way to uncover some of these plant-animal interactions. They bought teas and herbs from a grocery store and tested the dried, packaged leaves for tiny remnants of DNA, a method called Environmental DNA or eDNA analysis. In their recent studyPosted in Biology Letters, the team found traces of more than 1,200 different arthropod species from their analysis of just four plants: chamomile, mint, tea and parsley. This method can be applied to all dried plants, making it a potentially valuable tool for monitoring endangered insect species and tracking the spread of crop pests.
The researchers chose teas and herbs for their eDNA study because commercial products made from them included leaves that had been crushed and dried. “In a sample like coffee, which is very heavily processed, there’s probably very little DNA left,” says Krehenwinkel, “so we tried things that were as natural as possible.”
The scientists scoured local grocery store shelves for herbs and teas from four continents. They purchased multiple versions of the same product but from different brands to ensure that each tea had a range of origins represented, which would maximize the number of arthropods they could find. “I basically just went to a few different grocery stores and bought a whole bunch of different types of tea that they had,” Krehenwinkel explains. “They must have thought I was a heavy tea drinker.”
The team had to develop methods to extract and amplify arthropod DNA from all the plant material. The vast majority of tea leaf DNA comes from the tea plant itself. “Probably 99,999, or something like that, percent of the DNA that we extract is plant DNA, and only a tiny fraction, that’s left, is insect DNA,” Krehenwinkel explains, “that which, of course, is good for tea drinkers because they want to drink the tea and not the insects.
He adds that even a tiny presence of arthropod DNA is a good sign that the tea isn’t dripping with pesticides.
Researchers have discovered how to isolate arthropod DNA by finding a key sequence that differs between arthropods and plants. The team discovered, on average, more than two hundred different types of arthropods from each tea sample. Not all of these animals could be matched to known species, highlighting the need for further research into the more obscure and less studied groups. But those that were identified generally matched known plant and arthropod distributions. For example, mint tea contained DNA from insects found in the Pacific Northwest region of the United States, while green tea contained DNA from insects native to East Asia. East.
Being able to analyze the eDNA of commercial teas could facilitate the collection of data on insects around the world. According Eva Egelyng Sigsgaard, a molecular ecologist from Aarhus University who was not involved in this study, a common problem with many eDNA studies is the limited volume of samples that can be obtained by a small team of researchers. The use of commercially produced teas and herbs circumvents this problem by taking advantage of the existing infrastructure for harvesting, drying and transporting plant material. “You could even say that the sampling was done to some extent, unintentionally, by those companies that made those products,” says Sigsgaard.
Analyzing arthropod DNA from tea leaves or other dried plant material could help scientists track the spread of insects considered pests. Insects are often inadvertently transported around the world, wandering around in cargo ships, potted plants, or firewood. While most will not survive the journey, some species move successfully and continue to wreak havoc on forests or crops. Being able to detect pest species soon after they appear in a new area could help start the management process before pest populations skyrocket.
Other dried plants could also be analyzed using the same eDNA methods from this study. Krehenwinkel is particularly interested in extracting arthropod electronic DNA from dried plants that were collected decades ago and carefully stored in museum collections. These eDNA results can then be compared to those of modern plants from the same places to see which arthropod species have come and gone.
As Krehenwinkel envisions, these comparisons of old and new plant samples will provide a way to “go back in time and understand how communities have changed.” This historic lens could be useful for insect conservation efforts, especially in light of the decline of insects. While scientists know that many insects are endangered due to threats such as climate change and habitat degradation, they struggle to quantify the extent of these losses.
Julie Lockwood, a Rutgers University ecologist who was not involved in this study, points out that comparisons of eDNA from old and new plant material could also help scientists discover when an insect species was introduced for first time, intentionally or not, in a new area. “The question is often when did this species first appear?” she explains: “We don’t know. We get the first recordings: the first time someone saw them. But it can take decades after they arrive.
Krehenwinkel’s team also wants to use their methods to engage children in ecology and conservation by providing a hands-on way to contribute to ongoing research. While the actual molecular analysis requires expensive high-tech equipment, collecting and drying plants is easy to do at home. Krehenwinkel explains that with just an envelope, a Ziploc bag, and a few sachets of silica — like the ones that come in pill bottles to absorb moisture — kids can quickly collect and dry the plants for use in future research on eDNA.
“You just give a little plant-collecting kit to a child, and then they can collect flowers, and basically we can process those flowers and reconstruct those interactions,” Krehenwinkel says. He adds that he hopes “that with these community science projects, we will be able to obtain large-scale information on plant-insect interactions”.