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222 M. A. Hulme and G. W. Green
laricella, G. hercyniae. L. salicis. O. brumata, and P. erichsonii continue to be controlled
by introduced parasitoids (Table 53), as does R. buoliana, provided temperatures favour
parasitoids by synchronising their development with nectar and pollen supplies. These
supplies are provided by encouraging the growth of flowering plants such as buckwheat
(Fagopyrum esculentum Moench), wild carrot (Daucus carota L.). and milkweed (Asclepias
syr;aca L.). This effective and novel approach emphasizes the importance of examining
several alternative tactics for inoculating and establishing the control agent in the pest
population. The geographic range of control of some of the above insect pests does not yet
cover the entire country and attempts are now being made to control, for example. C.
laricella in western Canada by introducing a braconid, an ichneumonid and two eulophids
similar to those that are successful in eastern Canada.
Several new subjects were chosen for control attempts. Small introductions of braconids
and ichneumon ids were made to control C. serratella, so far without success.
However, prospects still seem good because these parasitoids are important regulators
of populations in Europe. Limited introductions were made against F. pusilla and at
least one of the parasitoids has become established, although it is too early to evaluate
control potential. P. geniculata was chosen as a promising candidate for control because
it is so heavily parasitized in its native Europe that once sufficient numbers of the
ichneumonid were received from Europe good local control was obtained. underlining
the importance of making adequate releases. Attempts against C. fumiferana are not
evaluated here because they essentially did not progress beyond cage studies. Attempts
against N. swaine; are also not evaluated because they involved release of a general
predator of many forest pests.
Entomopathogens
Entomopathogens have been used for most of our current biological control attempts
against native pests, mainly by attempting to inundate the environment of the pest
insect. In general. entomopathogens must be applied early in the insect's development if
foliage is to be saved in the year of application. Early application is particularly important
when viruses are used.
Remarkable progress has been made with B.t. during the review period. Improved
strains of B.t. (Dulmage 1970) followed by improvements in formulation and application
technology have now reached the point where many forest managers find B.I. can be as
effective as chemical insecticides against C. fumiferana (e.g. Dorais el al. 1980); costs
are three to five times higher. It is. of course, essential that the material be applied at the
correct time, in adequate dosage, and with good application techniques that include
suitable formulation of the spray ingredients. Many of these developments with B.I.
sprays have not yet been adequately tested on other Lepidoptera but there are no a
priori reasons why success should not be similar.
Recent success with viruses has been outstanding. Effective viruses were found
against all the tested neodiprionid sawflies, with the possible exception of N. ab;etis,
where sufficient data are not yet available to make an assessment. The NPV of N.
leconlei has been particularly successful in spreading from the point of application
(apparently via predacious and scavenging insects) and has allowed spot introductions
to be used. Observations suggest that many applied viruses continue to exert control in
the years following application, although it is not yet clear in many cases how this carryover
is achieved. The virus may infect offspring transovarially, for example. or the virus
may simply contaminate the environment by residing in cadavers. twig crotches, and
other protected locations. Further research is required to elucidate the specific mechanisms.
Effective viruses were also found that could control certain Lepidoptera, notably the
NPVs for O. leucostigma and O. pseudotsugata. Success against C. fum;ferana and L.
dispar has been only marginal because of the lower virulence of the viruses tested.