Since its introduction more than a century ago, garlic mustard (Alliaria petiolata) has rapidly spread across much of the Midwestern and Northeastern United States. Tolerant of shade, it aggressively advances through woodland areas, often forming dense stands and outcompeting native plants. Over decades, this advance has dramatically changed the balance within our woodland ecosystems, reducing the diversity of native plant species and altering the habitat that native snakes, salamanders, insects and birds depend on for survival.
When plants are introduced to a new area, the specialized insects that fed on them in their home region do not always accompany them. This gives the introduced plant a competitive advantage over native plants that share the same ecological niche. In some cases, humans will identify and introduce insect herbivores from the plant’s home region to help even the playing field. This practice is called classical or introduction biological control. In other cases, insects from the plant’s native range get introduced accidentally. Less commonly, generalist native herbivores may begin to include the introduced plant in their diet. The result, over time, is a whole suite of insects that attack the introduced plant in its new range and help reduce its impact on native ecosystems. The story of garlic mustard in North America could serve as a textbook example of this phenomenon. A variety of native North American insects feed on it, as do several insects originally from elsewhere. Unfortunately, this herbivory has not yet risen to a level that keeps garlic mustard in check.
There is some good news though. In a report published in 2022 by Doris Lagos-Kutz et al., a European species of aphid that had not been previously recorded in North America was identified feeding on garlic mustard in Ohio. This species, the garlic mustard aphid (Lipaphis alliariae Müller), is a specialist that is adapted to only feed on garlic mustard. Researchers are investigating the potential impact this species might have on garlic mustard in North America and they are asking for sightings to be reported. You can find more information by following the links in the resources section of this article (below).
Besides the garlic mustard aphid, there are at least six other species of aphid that are known to feed on garlic mustard in North America. These tiny insects can be surprisingly similar and difficult to differentiate from each other without viewing them under a microscope. We decided to take this opportunity to help familiarize residents with Lipaphis alliariae and some of the other aphids that also use this invasive plant as a host.
Garlic mustard aphid, Lipaphis alliariae (Müller)
This aphid has a dark blue/green to almost black body. The adult body size is 1.6 – 2.1 mm. Immatures are smaller and have dark colored patches along the back. Adults are more uniformly dark colored. These aphids prefer to feed on the developing seed pods of garlic mustard but they can also be found on stems and leaves.
Source: msu.edu
Photo Credit: pexels-tom-van-dyck
Categories: Michigan, Crops