Garlic mustard biocontrol: ecological host range of biocontrol agents

Background

Garlic mustard is a noxious biennial herb whose invasive range includes 37 US states and 6 Canadian provinces. Current management options are limited to time-intensive manual removal or costly chemical control.

Although garlic mustard was originally introduced from Europe for use in cooking, few insects or wildlife will readily eat the plant. One group of beetles, however, does feed almost exclusively on garlic mustard: European weevils of the genus Ceutorhynchus. These non-native weevils present an exciting opportunity for a long-term, sustainable biocontrol program in the United States. The long-term goal of this project is the safe, effective implementation of such a program.

Experiments will focus on Ceutorhynchus scrobicollis and Ceutorhynchus constrictus, which are known to feed on garlic mustard’s leafy crown and seeds, respectively. C. constrictus can reduce garlic mustard seed production by up to 60.5%, and field attack rates of C. scrobicollis can reach 100%.

Researchers will expand on prior work to determine the weevils’ host plant range, impact on native plant populations and likely distribution following release. Together, these data will establish whether Ceutorhynchus poses a threat to nontarget plants as it moves forward towards USDA approval for field release.

Research questions

• What is the host range of the seed feeder weevil C. constrictus?
  
  
• What impact does the crown eater weevil C. scrobicollis have on key native plants, including Brassica species that are biologically similar to garlic mustard?
  
  
• What is the expected distribution of C. scrobicollis and C. constrictus should they be released for biocontrol?
  
  
• What method will be used to meaningfully monitor garlic mustard control at weevil release sites?
  
  

Practical implications

Once approved by the USDA, this will be the first garlic mustard biocontrol program in North America. These efforts promise to reduce the negative impacts of garlic mustard on native woodland species, reduce the long-term labor and monetary costs of control and remove one of the obstacles for the regrowth of key species like oak in our Minnesota woodlands. Researchers anticipate up to 100% control with the use of simultaneous use of both Ceutorhychus species.

Details

Funding:

$600,000

Collaborators:

CABI, USDA, Minnesota Department of Natural Resources (DNR)

Research Team:

Roger Becker, principal investigator

Elizabeth Katovich, researcher