A guide to aphids that feed on garlic mustard in Michigan
Print
EmailCan these tiny insects help in the fight against invasive plants?
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.
Cabbage aphid, Brevicoryne brassicae (Linnaeus, 1758)
The cabbage aphid has a gray-green body. However, the body is covered with a whitish waxy coating that gives it more of a gray-white appearance. The mature cabbage aphid’s body is 2.0 – 2.5 mm long. The name of this aphid comes from the Latin word for “short” combined with the Greek word for “club,” referring to two short tubes (cornicles) on the posterior of the aphid. Cabbage aphids prefer to feed on brassicas, such as cabbage and various greens.
Green peach aphid, Myzus persicae (Sulzer)
Green peach aphids come in an array of colors. Most of the time, you will find them to be green, yellow or yellowish green. However, some individuals may be pink, orange or dark green under certain conditions. Green peach aphids do not have a whitish waxy coating. The mature aphids’ bodies are 1.8 – 2.3 mm long. This aphid prefers to feed on the leaves, flowers and fruit of peach, cherry and plum trees.
Turnip aphid, Lipaphis pseudobrassicae
These are yellowish green to dark green aphids. Like the cabbage aphid, they have a whitish waxy coating, but it is not as thick in this species and may be less apparent in some cases. The body length of the turnip aphids ranges from 1.4 – 2.4 mm. This aphid is a significant pest of cole crops the world over and prefers to feed on tender new growth or young plants.
|
Comparison of four of the aphid species that might be found on garlic mustard. |
|||
|---|---|---|---|
|
Aphid species |
Body length (mm) |
Color |
Waxy coating |
|
Garlic mustard aphid |
1.6 – 2.1 |
Dark blue/green |
No |
|
Cabbage aphid |
2.0 – 2.5 |
Whitish green |
Yes |
|
Green peach aphid |
1.8 – 2.3 |
Yellow, green, pink |
No |
|
Turnip aphid |
1.4 – 2.4 |
Yellow-green, dark green |
Yes |
Garlic mustard aphid resources
- Original research article: New records of invasive aphids (Hemiptera: Aphididae) on garlic mustard in the USA
- Brochure with instructions for how to report sightings from the Midwest Invasive Plant Network: Be on the Lookout: Help Us Find Garlic Mustard Aphids
- Website for reporting sightings: EDD Maps
