Phenology and dispersal of Larinus minutus Gyllenhal and Larinus obtusus Gyllenhal (Coleoptera: Curculionidae), two biological control agents of Centaurea stoebe ssp. micranthos (spotted knapweed) in Michigan

• Published in: Biological control 2014-12, Vol.79, p.84-91
• Main Authors: Carson, B.D., Landis, D.A.
• Format: Article
• Language: English
• Subjects: Animal, plant and microbial ecology; Applied ecology; Biological and medical sciences; Biological control; Centaurea; Centaurea stoebe; Coleoptera; Curculionidae; Dispersal; Fundamental and applied biological sciences. Psychology; Larinus minutus; Larinus obtusus; Parasitic plants. Weeds; Phenology; Phytopathology. Animal pests. Plant and forest protection; Weeds
• ISSN: 1049-9644; 1090-2112
• DOI: 10.1016/j.biocontrol.2014.09.001

[Display omitted] •We monitored the phenology and dispersal of Larinus spp. populations in Michigan.•Adults were present in easily detectable densities from mid-June through August.•Populations of Larinus spp. weevils showed little dispersal for 2years post-release.•After initial establishment, dispersal rates increased exponentially with time since release. Centaurea stoebe L. ssp. micranthos (Gugler) (spotted knapweed) is an invasive plant that has been the target of classical biological control in North America for more than four decades. The seedhead-feeding weevils Larinus minutus Gyllenhal and Larinus obtusus Gyllenhal (Coleoptera: Curculionidae) are two of the most-widely released C. stoebe control agents, and have more recently been introduced into the eastern US. While there have been many studies focusing on their ability to impact C. stoebe in the western US and Canada, there have been few studies from eastern North America, and basic knowledge of important aspects of their biology is lacking. Here we report on the phenology and dispersal of L. minutus and L. obtusus in Michigan. We regularly sampled two established Larinus spp. populations in southern Michigan in 2012 and 2013, and found that while adult abundance fluctuates during the growing season, they remained at easily detectable levels from mid-June through the end of August. We also used previously established populations of L. minutus and L. obtusus released in 1996 (n=1), 2007 (n=2), and 2010 (n=5) to determine how dispersal of Larinus spp. into the surrounding landscape changes with time since release. Populations of Larinus spp. weevils showed little dispersal for 2years post-release. However, after initial establishment dispersal rates increased rapidly, resulting in average dispersal rates that increased exponentially with time since release. These findings can inform future biological control release and sampling programs for Larinus spp. in eastern North America.