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Insects, presented as both pests and food resources of the future, are of great importance for the balance of all ecosystems around the world. But climate change, the use of many insecticides, pesticides and fertilizers are drastically reducing their biodiversity and endangering some key species. Recently, a group of German researchers found traces of DNA from several hundred insects in tea bags and dried herbs. These tiny remnants, preserved among dried leaves, could help scientists track down pests and watch for declining populations of insects essential to our survival, such as bees.
All scientists say that 40% of insects are in decline. In 30 years, insect populations in Europe would be reduced by 80%. About 75% of terrestrial biodiversity is maintained by a complex system of interactions between plants (known as hosts), herbivorous insects, and their associated predators (often other arthropods).
Thus, insects occupy a central place in the living world: to date, scientists have inventoried about 1.1 million species, and their number is estimated to be between 6 and 7 million. This group of animals is critical to the balance of the global ecosystem, whether they are decomposers, detritus feeders, herbivores or pollinators. Their interaction with plants is co-evolutionary in nature, a kind of arms race that supports biodiversity.
Therefore, their study is a serious problem, but, unfortunately, modern methods of enumerating them are not very effective. Until now, insects had to be caught in traps. The disadvantage of this practice is the high mortality of captured insects. Not to mention that usually only a few of the insects that come into contact with the plant are captured and therefore included in the analysis, obscuring a large number of other species equally important to the plant.
Recently, Henrik Krenwinkel from the University of Trier (Germany) presented a new method for obtaining and evaluating environmentally significant DNA (eDNA) from dried plants. Environmental DNA is DNA collected from the environment rather than directly from the body. Its collection makes it possible, thanks to genetic tools such as metabarcoding, to identify the species from which it is descended. Their method is published in the journal Biology Letters.
A cup of tea with a cloud of insect DNA
The ability to collect eDNA virtually anywhere in the environment—in water, soil, or on plants—allowed the rapid development of biomonitoring, observation, and observation of animals and plants in recent years.
The innovation of the method developed by Henrik Krenwinkel, Sven Weber and Susan Kennedy is that eDNA is taken from crushed and dried plant material. They developed a metabarcoding assay to selectively enrich arthropod DNA from homogenized plant extracts while preventing plant DNA amplification by a key sequence that differs between arthropods and plants. With this test, they analyzed various commercially produced teas and herbs, but not coffee. Indeed, the latter undergoes too many transformations before being sold, losing all traces of insect DNA that could communicate with the plant.
Thus, the samples revealed ecologically and taxonomically diverse communities of arthropods, numbering in total more than a thousand species in more than 20 orders, many of which are specific in terms of host plant and geographical origin. For example, mint tea contained insect DNA from the Pacific Northwest region of the United States, while green tea contained insect DNA from East Asia.
Henrik Krenwinkel explains in a press release: “We studied commercially available teas and herbs and found the DNA of up to 400 different insect species in a single tea bag.” The presence of insects in tea bags is a good indicator for consumers, as it indicates little or no use of insecticides.
Many scientific, educational and even criminal projects
Given that DNA is rapidly destroyed by ultraviolet radiation or washed away by rain, scientists have made a startling discovery. This DNA found in dried plants is surprisingly stable. So Henrik Kreenwinkel wants to use plant collections that have been archived for decades to see if biomonitoring can be tracked over a long period of time with their method.
Observing interactions between plants and insects is of particular interest to science in terms of observing the evolution of biodiversity. Insect species associated with certain plant species have previously been shown to die out with the plants, and vice versa. With the help of eDNA, researchers could take a fresh look at the reasons for this decline.
A green rice beetle crawls on a leaf and leaves traces of DNA. © Willibald Lang
Apart from this biomonitoring, dried plant material is well suited for pest control. Many pest species live secretly on or inside the host plant, making them difficult to detect. Invasive pests are often not recognized until they have reached very large population sizes. Regular sequencing of dried plant samples will allow the detection of such cryptic pests well in advance of their outbreaks, or allow the detection of pests in warehouses.
There are also many possible applications, from environmental education and information projects to criminal research. Henrik Krenwinkel explains: “We are currently working on simplifying the protocol of our procedure so that school classes can work with it. Ultimately, this could lead to a citizen science project where citizens will conduct biodiversity research.”
Finally, the procedure can also be a valuable tool for Customs. Indeed, reliable statements about the true geographic origin of plants can be made with eDNA. In this way, customs can determine whether the imported teas are indeed from the designated countries. What is possible with tea also applies to other herbal remedies.
The authors note that their method still requires further standardization. Not to mention, it remains to be seen whether certain taxa are missed in the analysis, for example because they deposit less eDNA on the plant. The video explains how researchers obtain and process eDNA from crushed and dried plant material.