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1 results

  • Distribution of Urophora affinis and U. quadrifasciata, Two Flies Introduced for Biological Control of Spotted Knapweed (Centaurea maculosa) in Montana

  • Jim M. Story, Robert M. Nowierski, Keith W. Boggs
  • Journal:
    Weed Science / Volume 35 / Issue 2 / March 1987
    Published online by Cambridge University Press:
    12 June 2017, pp. 145-148

  • A survey was conducted at 88 sites in Montana in 1984 and 1985 to determine the distribution of Urophora affinis Frauenfeld and U. quadrifasciata (Meigen), two seed head flies released on spotted knapweed (Centaurea maculosa Lam. # CENMA) in North America. U. affinis, released in Montana during 1973 to 1977, was found at 40 of the 88 sites. The fly was concentrated within a short radius (about 5 to 8 km) of release sites, even at sites having well-established populations. U. quadrifasciata, released in British Columbia in 1972, but not in the United States, was found at 84 sites. The data suggest that the fly entered the state in the northwest corner and dispersed in a southeasterly direction. There was a strong positive relationship between mean number of galls per seed head and percent infestation for both fly species.