By Carolyn Bernhardt
Researchers from Cornell University have developed tools to help fight the hemlock woolly adelgid (Adelges tsugae), a pest responsible for killing hemlock trees across eastern North America. A new study published this month in the Journal of Economic Entomology details work on innovative DNA tests to accurately detect the beetle that eats hemlock woolly adelgid, making it easier to track and measure the impact of these helpful insect allies.
Since arriving in the 1950s, the hemlock woolly adelgid (HWA) has caused the widespread death of eastern hemlock trees from northern Georgia to Maine, extending westward into states such as Michigan, Ohio, and Kentucky. This devastation not only affects native tree diversity across the region but also harms native bird species in the forests of New England and the mid-Atlantic.
Hemlocks thrive on steep slopes, canyons, and ravines, which makes chemical pesticide applications both challenging and expensive. For a more sustainable approach, scientists have enlisted the help of natural predators, the Derodontid beetles Laricobius nigrinus (first released in 2003) and Laricobius osakensis (first released in 2012), which can access the trees and seek out HWA much more easily than humans can. However, distinguishing between these beetles during their larval stage, or even detecting their presence at all, has proven challenging due to their strikingly similar appearance and behavior. Thus, an efficient and low- cost monitoring approach using environmental DNA (eDNA), in which organisms can be detected by the genetic material they leave behind in an environment, is in demand for forest management.
While L. nigrinus is native to western North America, L. osakensis colonies used for biocontrol originate from Japan. Both species can establish and spread in eastern North America, but they may differ in how well they work as biocontrol agents. The researchers’ goals in the new study were twofold: to develop new tools capable of differentiating the biocontrol beetles and to assess the effectiveness of detecting beetle DNA in environmental samples.
The scientists focused on a specific beetle DNA segment called CO1, commonly used in genetic studies to identify and differentiate species. According to lead author Fangzhou Liu, Ph.D., CO1 gene sequences are very similar across different beetle species, showing little variation. This high degree of similarity indicates that the gene has remained relatively unchanged through evolution, making it challenging for researchers to design specific tests to differentiate between the beetle species because their CO1 gene sequences are almost identical.
However, effectively monitoring released beetles is integral to evaluating how successfully they work as biological control measures against HWA. “Accurate identification of these species, whether larvae or adults, is crucial for data analysis and result evaluation,” says Liu, a postdoctoral associate at Cornell in the Department of Natural Resources and the Environment.
So, the team decided to design new primers and probes to target L. osakensis DNA specifically. Primers and probes are essential components used in genetic testing methods like PCR and qPCR (quantitative polymerase chain reaction). Primers, short DNA pieces that attach to the target DNA, work with probes, which light up (e.g., via fluorescence) when they find the target DNA to show researchers when the DNA they are looking for is present in a sample.
“Our primers and probes successfully distinguished L. osakensis from other beetles,” says Liu. “The assays showed high sensitivity, detecting eDNA at very low concentrations.” They can be used to find L. osakensis DNA in environmental samples like soil or water, offering a crucial tool for monitoring beetle populations in their natural habitats. Liu also says the primers and probes the team developed work with both “SYBR green” and “TaqMan” probe techniques, methods experts often use to study DNA. This flexibility makes the probes and primers highly adaptable to various laboratory conditions, enhancing their practical utility in genetic analysis.
However, the study only tested simulated environmental DNA (eDNA) samples in the lab rather than actual field samples. In future studies, they plan to sample in natural settings and explore how these methods can track the spread of these biocontrol agents.
Still, using cost-effective, flexible reagents to improve test performance and developing a new, more accurate method for determining the best temperature for DNA primers helps advance the overall accuracy and reliability of the DNA detection process. That means the implications of these findings extend beyond beetle identification, offering promising prospects for environmental DNA analysis and species monitoring in other challenging ecological settings. For example, the study provides ideas and references for other studies, such as testing and selecting more sensitive reagents and more suitable qPCR program parameters.
As the research progresses, the team is eager to apply their findings in practical settings, hoping to bolster other conservation efforts. “While our study focused on identifying and monitoring specific beetle populations, we believe our methodologies could be adapted to diverse ecological contexts, catalyzing more efficient environmental management strategies,” Liu says. “I really hope that life science researchers pay attention to the design concepts and strategies we presented regarding reagent selection. They are likely to solve many methodological challenges that scientists are currently facing.”
“Environmental DNA assays for Laricobius beetles (Coleoptera: Derodontidae), biocontrol agents of the hemlock woolly adelgid in North America ”
Journal of Economic Entomology
Carolyn Bernhardt, M.A., is a freelance science writer and editor based in Portland, Oregon. Email: carolynbernhardt11@gmail.com.
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