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120 P. Harris
Table 25
may have been caused by cattle consuming the terminal flower heads, which contained
the highest numbers of R. conicus. The cattle did this to an increasing extent as the
density of the stand declined. The site was not grazed in 1982 and the density of weevils
increased.
Establishment pattern of R. conicus Froel. on C. acantlloides L. and C. nutans L.
C. acantlloides (Site A) at Read, Ontario. Released 320 R. conicus 25 July 1968,282 on
23 May 1969, 350 on 10 June 1970.
Calc. R. coniclls
Year Eggsffhistle per head No. thistles sampled
1968 0 0
1969 0.29 0.017 1453
1971 0.38 0.023 285
C. acantlloides at Roslin, Ontario. Released 4320 R. conicus on 11 July 1969.
Calc. R. conicus
Year Eggs/thistle per head No. thistles sampled
1969 0 0
1970 0.52 0.03 1531
1970· 1.56 0.09 50
1971 0.18 0.01 1272
• On scattered C. nutans in C. acantlloides stand.
C. nutans at Aylesbury, Saskatchewan. Released 400 R. conicus 26 July 1968, 1898 On
16 July 1969.
Year R. conicuslhead No. heads sampled
1969 0.08 317
1970 0.04 1055
1971 0.06 688
1972 0.26 847
1973 0.79 956
1974 2.72 311
1975 3.68 288
1976 1.43 182
1977 0.43 353
1978 2.70 251
1979 0.86 349
1980 0.40 293
1981 0.06 54
1982 3.18 105