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

Rate of dispersal of spotted knapweed biocontrol beetles (Larinus spp. Curculionidae) in Wisconsin

“…3) and our average annual dispersal rate consistently increased with time. Similarly, Carson and Landis (2014) also found a pattern of increasing Larinus spp. dispersal rate as time since release increased; although our observed dispersal rates are higher than those reported in that study and others.…”

“…dispersal rate as time since release increased; although our observed dispersal rates are higher than those reported in that study and others. Carson and Landis (2014) observed at a site 6 years post release that Larinus minutus moved on average 1.0 km/yr (n=1) and L. obtusus moved 3.5 km/yr (n=1). Our results showed an average annual dispersal of 9.5 km/yr (n=3) for Larinus spp.…”

“…First, differences could result from differences in survey methods. Carson and Landis (2014) sampled in all 4 cardinal directions in set intervals of 100 m, 500 m, and 1000 m, and if no Larinus spp. were found at those intervals sampling was discontinued, but if they were detected then sampling occurred at 3000 m, then 8 km, and then 16 km.…”

“…were found at those intervals sampling was discontinued, but if they were detected then sampling occurred at 3000 m, then 8 km, and then 16 km. Carson and Landis (2014) acknowledge that their estimated dispersal rates were conservative. Our method was to gradually leave the dense population of Larinus spp.…”

“…A field study done by Groppe et al (1990) found evidence that L. minutus undertakes dispersal flights. A recent publication in Michigan showed an average dispersal rate of 1 km/year for L. minutus, and 3.4 km/year for L. obtusus on sites 6 years after initial release, and 8.5 km/year for L. minutus 17 years after release (Carson and Landis, 2014). In the Nelson Forest Region in British Columbia, Canada in 2001, L. obtusus dispersal was estimated at 1.5 km/year 8 years after initial release (Ministry of Forests, 2002).…”