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122 P. Harris
Table 26 C. flU/ailS L. stands at Aylesbury and Findlater following establishment of R. coniclls
Froel. (± S.E.M.).
Year No. C. tIIltallS/m 2 No. heads/plant Head diameter No. plants sampled
Aylesbury
1969 15.9 ± 1.7 5.7 ± 0.8 2.87 ± 0.02 56
1970 11.8 ± 1.1 7.5 ± 0.9 1.68 ± 0.03 125
1971 6.8 ± 0.7 6.2 ± 0.8 2.02 ± 0.03 100
1972 604 ± 0.8 8.0 ± 0.9 1.65 ± 0.02 106
1973 704 ± 1.1 1.79 ± 0.02 129
1974 4.1 6.6 ± 1.3 1.73 ± 0.02 47
1975 4.9 404 ± 0.7 1.94 ± 0.02 65
1976 6.6 ± 104 304 1.73 ± 0.01 54
1977 1.3 ± 0.3 6.0 ± 0.3 1.55 ± 0.02 60
1978 1.2 ± 0.5 4.3 ± 0.8 1.52 ± 0.03 58
1979 104 ± 004 3.9 ± 0.7 1.38 ± 0.02 89
1980 1.9 ± 0.7 2.3 ± 0.1 1.16 ± 0.05 124
1981 0.9 ± 0.4 1.5 ± 0.1 1041 ± 0.02 60
1982 0.5 ± 0.1 2.8 ± 0.5 1.56 ± 0.04 38
Findlater
1969 l3.5 ± 2.6 11.9 ± 1.8 1.80 ± 0.04 10
1970 19.1 ± 2.5 10.0 ± 1.3 1.98 ± 0.02 51
1971 19.8 ± 2.8 4.9 = 0.5 1.69 ± 0.04 40
1972 8.0 ± 1.2 6.9 = 0.7 1.70 ± 0.02 35
1973 5.3 = 1.0 1.87 ± 0.04 32
1974 19.9 5.9 ± 1.2 1.95 ± 0.01 35
1975 52.1 2.9 ± 0.7 1.86 ± 0.06 18
1976 7.2 4.2 ± 0.6 1.81 ± 0.03 24
1977 0.4 ± 0.2 5.2 ± 0.2 2.03 ± 0.03 19
1978 33.9 ± 5.7 2.3 ± 0.3 lAO ± 0.05 38
1979 6.7 ± 0.1 5.2 ± 0.8 1.19 ± 0.03 33
1980 3.0 ± 0.7 3.6 ± 0.3 1.19 ± 0.03 104
1981 0.6 ± 0.3 4.0 ± 1.6 1.39 ± 0.06 24
1982 0.03- 11.6 ± 1.8 1.83 ± 0.02 32
- 1 thistle in 37 m 2
persisted at another site in Regina on a 10 m 2 stand of C. nlltallS with around SO flowering
thistles. If the weevil requires dense stands, even if they are confined to a few m 2 , the
roadside and gravel pit stands may be necessary for maintaining a population.
Size of C. nU/alls
The size of flowering C. 'IlltallS plants as indicated by the number of heads/plant
declined (Table 26). The slope of the decline was not significantly different at Aylesbury
and Findlater, so the data were combined for the regression in Table 27 (Equation 1).
The only major departure from the regression was the 1982 value from Findlater. This
value was not used for the regression as it was not from the permanent transect. The
equation shows that on the average a plant produced 0.34 fewer heads each year. Thus