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Author: Brandi H. Misiaszek
Chinese privet (Ligustrum sinense) is an invasive shrub native to Asia. This genus of shrubs is commonly used as an ornamental plant due to its attractive appearance. Although it was intentionally introduced to the United States as an ornamental, Chinese privet is now considered one of the worst invasive weeds in the southeast. There is currently no effective control method implemented for the Chinese privet, however biological control may already be occurring due to another unintentionally introduced species, the seed-feeding ligustrum weevil (Ochyromera ligustri).
Chinese privet was introduced to the United States as an ornamental plant from Asia in 1852 (Dirr, 1983). The shrub ended up escaping cultivation, forming dense stands, thus outcompeting and displacing native vegetation in the forest understory region. Because the plant exists in such large amounts, reducing biodiversity and altering our native ecosystems, it is considered one of the worst weeds of the Southeastern US.
Chinese privet berries with Ligustrum weevils.
The Chinese privet is a shrub, typically 5-12 feet tall, in the Olive family (Oleaceae). The tree produces white flower clusters that develop intoberries. When immature the berries are green, and turn purple when mature. The leaves are opposite, with entire leaf margins (smooth edges), and semi-deciduous (Ursbatsch, 2006). Chinese privet can sometimes be confused with the less invasive Japanese privet (Ligustrum japonicum), which can be differentiated by Japanese privet’s glossy leaves.
Japanese privet on the left and Chinese privet on the right.
Chinese privet flowers.
Chinese privet berries.
Chinese privet reproduces both asexually and sexually. This means, new plants can sprout from root systems and by berries. Once established, the plant spreads easily because of the large seed banks and extensive root systems (Ursbatsch, 2006). Both privet berries and the ligustrum weevil can be dispersed long distances by berry-feeding birds. There are accounts of birds consuming the berries and excreting the seeds with live weevils still inside. This disperses the seed, and thus weevil inside, wherever the birds decide to defecate (Chen, 2021).
Chinese privet reports show a dominance in the southeastern US. However, isolated reports occur in California and Oregon, as well as New York and Rhode Island.
Key: Each gray dot is a Chinese privet (Ligustrum sinense) observation.
The ligustrum weevil (Ochyromera ligustri) is a non-native beetle, first discovered in the US in 1959. It is most likely that the weevil arrived through the privet trade. The ligustrum weevil is native to Asia where it serves as a natural enemy of privet in that region. Now located in multiple southeastern states, the ligustrum weevil also serves as a natural enemy of privet in the US, too. It is currently unknown what the exact distribution and impact of the ligustrum weevil is in the US.
Ligustrum weevil.
Ligustrum weevils belong to the Curculionidae family. They are brown, small to medium sized beetles. They have the characteristic weevil “snout”, and what makes them unique is their “thorns” on their profemora (front legs[1] ). The egg, pupal, and larval stages have not yet been formally described.
Ligustrum weevil. Image source: Cuda and Zeller, 2005
Currently, it is known that ligustrum weevils feed on Chinese and Japanese privet (both non-native) in the United States, but host-range testing is in the works. The adults primarily feed on the leaves of the plant, creating small “bullet holes” in the foliage. Females oviposit their eggs into the berries of the plant, commencing development of the larvae within the seeds. They pupate within the seed and emerge as an adult (Cuda and Zeller, 2005). This effectively destroys the seed within the berry, thus destroying its reproductive capacity.
Chinese privet berry with weevil entry hole.
Chinese privet leaves with adult feeding damage.
Because ligustrum weevils destroy Chinese privet seeds, they could be a great candidate for a biological control agent. By destroying the seeds, they limit the reproductive capacity of the plant. Adult feeding damage is not enough to control Chinese privet, however in large amounts it may contribute to stress of the plant. The full effects of the Ligustrum weevil in the United States is currently being studied at the Louisiana State University Biological Control Lab.
The distribution of the ligustrum weevil is currently not completely known. The LSU Biological Control Lab is in the process of updating this distribution. See section “Current Research and How You Can Help!” to see how you can be involved in this process!
Key: Each gray triangle is a ligustrum weevil observation.
While not much is currently known about the ligustrum weevil in the United States, there is currently a research project occurring at the LSU Biological Control Laboratory. The four objectives of this research are: characterize any other herbivores or pathogens associated with Chinese privet in Louisiana, understand the impact and population dynamics of the ligustrum weevil, determining the US distribution of the ligustrum weevil, and characterizing the host range of the ligustrum weevil.
We are implementing a citizen science program in which citizens identify Chinese privet in their area and sending berries to the LSU Biological Control Lab. This program will allow citizens to gain knowledge on invasive species in their area, as well as help us update our ligustrum weevil (and consequently, Chinese privet) distribution. We will be using genetic techniques to identify weevil genetic material within the berries we receive. Then, we can identify where the weevils are present!
Dr. Rodrigo Diaz searching for ligustrum weevil on a beat sheet.
Bags of collections of Chinese privet berries.
Masters student Brandi Misiaszek using beat sheet method to search for ligustrum weevils.
Bonus points if you can spot the ligustrum weevil itself! If you find one, please upload to iNaturalist with a description of where you found the weevil (ex. On a Chinese privet leaf, on a berry, on a different plant, etc.). If possible, you can send the weevil to us. To do this, you can first harmlessly put down the weevil by putting it in a freezer for at least 48 hours. Then, package the weevil in either a ziplock bag, vial, or other small container. Then, mail to the aforementioned address and notify us.
To have some fun and go the extra mile, you can look for the weevil by using the beat sheet method. This video from Ohio State University is a great example on how to do this: How to Beat for Insects (Emily Justus). Another way we recommend doing this method is to hold an inverted umbrella underneath the shrub, allowing for insects to fall into it.
We thank you for your help, and hope that you have fun!!
Chen, Z., Guo, Y., Yang, J., Ge, J., Li, L., & Chen, G. (2021). Frugivorous birds disperse seeds of Ligustrum lucidum, seed‐feeding weevils, and parasitic wasps of weevils via endozoochory. Integrative Zoology, 17(5), 953–958. https://doi.org/10.1111/1749-4877.12606
Cuda, J. P., & Zeller, M. C. (2005, May). Featured Creatures - Ligustrum weevil. Ochyromera ligustri Warner. Retrieved from https://entnemdept.ufl.edu/creatures/orn/shrubs/ligustrum_weevil.htm
Dirr, M. A. (1983). Manual of woody landscape plants (3rd ed.). Stipes Publishing Co., Champaign, IL. 536 pp.
Urbatsch, L. (2006, October). Plant Guide - USDA Plants Database. Chinese privet Ligustrum sinense Lour. Retrieved from https://plants.usda.gov/DocumentLibrary/plantguide...
