Effects of the Interaction of the Biocontrol Agent Agapeta zoegana L. (Lepidoptera: Cochylidae) and Grass Competition on Spotted Knapweed

摘要: Abstract Agapeta zoegana is a Eurasian root-mining moth introduced for biological control of spotted knapweed, Centaurea maculosa, in North America. A study was conducted during 1992 through 1994 to assess the establishment and make preliminary assessment combined effects grass competition on knapweed plant structure density at two nearby sites western Montana. The well established release site where it had been previously released, became comparably check site, 140 m away, by 1994. Knapweed plants A. less above-ground biomass (43%), fewer stems per (29%), capitula (43%) were shorter (18%) than which may represent impact plant. However, comparison infested versus uninfested throughout both showed that more (15%), (40%), (112%), taller (7%), thicker roots (92%), older (22%) plants, suggesting preferentially attacked older, larger plants. Numbers larvae root positively correlated with diameter. Incidence attack significantly greater bolted rosettes, but no preference over rosettes when diameters similar. effect rosette density, appeared reduce number plots low (10% cover) 39% increase seedlings spring 65%. Plots high (50% contained (35%), (38%), (50%) density. not additive.