Weevil impact monitoring 



At all permanent monitoring sites, the presence/absence of weevil 

 infestation was noted on all flowering stems sampled for 

 hybridization monitoring (min. sample size: 20) for determining 

 the rate of infestation. Next, ten whole flowering plants were 

 collected a minimum of 10 m. beyond (generally downwind) of the 

 plot periphery in a destructive sampling procedure. All heads on 

 the plants were guartered and categorized as to degree of 

 infestation (0%, 1-25%, 26-50%, 51-75%, 75-100%). Infestation 

 data was recorded in sequence from top to bottom of the plant. 

 The number of infested heads per plant, and the very approximate 

 degree of infestation per infested head, were calculated. This 

 method is based on the USFS weevil impact method that was begun 

 in 1991 (Phillips and Field (1989-92), but incorporates a 

 doubling of the sample size (N=10) . 



In addition, a preliminary assessment of the density dependence 

 of infestation was made at the Russian Creek site, which had 

 plants in two different areas that differed in their densities by 

 orders of magnitude. It has been reported that Rhinocvllus 

 conicus are effective in drastically reducing the density of musk 

 thistle Carduus nutans ) , a noxious weed and intended host plant 

 for this introduced biocontrol agent (Kok and Surles 1975, 

 reported in Rees 1977) . 



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