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176 P. Hnrris nnd M. MlIw
Recommendations
beetle, C. hyperici, was needed to control the weed in moist sites. C. quadrigemina has now
become numerous at the moist sites of Fruitvale and Agassiz, British Columbia, although
C. hyperici has persisted and spread to other sites in the province (K. Williams 1981
personal communication). However, in spite of the release of pioneer moist-adapted
individuals of C. qlladrigemina with C. hyperici in the maritimes, the latter species has
become dominant and C. quadrigemina was not present in the samples examined. C. hyperici
is only slightly smaller than C. quadrigemina and the two species feed in a similar manner on
H. perforattun, so it is surprising that they coexist in the same habitats. It is not known what
occurred to allow C. quadrigemina to colonize moist habitats and invade the thriving colony
of C. hyperici at Fruitvale. The adaption has not extended to the maritimes and again the
reasons are unknown. From a purely pragmatic purpose of controlling H. perforatum the
important thing is that one species or another will reduce the weed to a low density in most
places in Canada. For example, at the release site in Ontario, the weed declined to only 0.2%
of its former density.
A strong colony of C. quadrigemina with some C. hyperici was established near
Guelph, Ontario, with stock from the Picton, Ontario, colony. A total of 7000 beetles
collected from the Guelph colony before its destruction in 1981 was distributed to 34
other sites in and around the city. By 1983 there should be massive populations of the
beetle in the Guelph area. These could be collected at little cost and released at other H.
perforatum sites throughout Ontario. Some of the releases would fail (two out of five
release sites of 1979 at Guelph were destroyed) but the beetle would distribute itself
from the survivors. The pilot studies at Picton, Ontario as well as those in British
Columbia indicate that the prevalence of H. perforatum would be greatly decreased by
such a programme with a corresponding increase in forage for livestock or wildlife.
The apparently few sites where Chrysolina spp. have been ineffective are on nutrientpoor
soils and in insecticide-drift areas. No insects are likely to be effective for biological
control if they receive an insecticide spray while they are exposed on their host
plant. It might be possible to find a root-boring insect that was inside the plant during the
spruce budworm spraying season; however, in view of the public outcry, the spray
programme is likely to become increasingly circumspect, so the problem for C. hyperici
should diminish.
More investigations are needed to determine whether the effectiveness of the Chryso­
Iina spp. can be increased on nutrient-poor soils; however, as the moth A. plagiata is
increasing on some of the areas not favored by the beetle, we already may have part of
the solution. Aphis chloris was chosen as a biological control agent as the presence of
symbionts in aphids often enables them to survive on plants that lack one or more
essential amino acids or B vitamins. However, its effectiveness as a biological control
agent for H. perforattun remains to be seen.
(1) C. quadrigemina and/or C. hyperici have shown that they are able to reduce H.
perforatum to well below the economic threshold in most regions of Canada. Any
province with H. perforaltun on their noxious weed list should distribute the beetles or,
if the importance of the weed does not justify this small effort, remove the weed from the
list.
(2) Provinces where the weed is being satisfactorily controlled should remove H.
perforalum from their noxious weed list as mowing or spraying operations against the
weed are a waste and not likely to assist its biological control.
(3) Further study is required to determine the role of Anaitis plagiata and/or Aphis
chloris.
(4) If further attempts are made to establish Agrilus hyperici, these should be done
by transferring the young larvae to plants in the field.