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216 M. A. Hulme and G. W. Green
Selection of Biological Control Agents
pusilla (Lep.), both of which feed on birch; the gypsy moth, Lymamria dispar (L.); the
balsam fir sawfly, Neodiprion abietis (Harr.), which, in the first review, was only examined
using surplus parasitoid stock; Bruce spanworm, Operophtera bruceata (Hulst); two
tussock moths, Orgyia leucostigma (J .E. Smith) and Orgyia pseudotsugata (McDunnough);
and the mountain-ash sawfly, Pristiphora geniculata (Htg.). Effort was almost equally
divided between treatments with entomopathogens and releases of predators or parasitoids.
The current review thus contains evaluations of control attempts against 21 insect
pests, although in some cases this simply entails updating assessments of control
attempts made during the previous review period.
Despite the increased number of pests covered in the current review, total effort
devoted to biological control of forest pests declined as the Canadian Forestry Service
went through a period of austerity. Work with predators and parasitoids suffered
particularly severe reductions of resources; and certain aspects of all programmes, such
as the population dynamics of the pest and of the control agent, were almost totally
neglected. These cutbacks are reflected in the lack of depth with which many of our
investigations were undertaken and inevitably reduced our chances of finding successful
controls. Despite these difficulties significant progress has been made, as detailed
later.
The definition of biological control of forest insect pests used in this review follows
that of the previous review - it is confined to the regulation of pest populations by the
introduction of parasitoids, predators, or entomopathogens. Population regulation is
considered acceptable if damage is controlled at tolerable levels in economic andlor
·0 social terms. The methods of introduction of the control agent cover all strategies from
inoculative releases of an organism, which then spreads through the pest population, to
augmenting agents already present in the pest popUlation, or to inundation of the pest's
environment with a control agent that mayor may not already be present (Knipling
1979).
The chapters that follow this overview are organized in alphabetical generic sequence,
and each chapter is written by the scientists responsible for conducting or assessing the
control attempts. An outline is given of the present status of the pest, background is
given where needed on reasons for the choice of control agents, and the authors'
evaluation is given of each attempt. Each chapter concludes with specific suggestions
for future work.
In describing the pest status, and in many of the assessments of control effectiveness
reference is made to the Forest Insect and Disease Survey (FIDS), an organization
within the Canadian Forestry Service that carries out major surveys of pest populations
and pest damage across the country. In earlier times surveys included routine rearings to
measure parasitoid levels in pest populations, but due to staff cutbacks such measurements
are rarely performed now and surveys by FIDS are generally confined to measurements
of pest numbers and pest damage. This in turn has seriously impeded the
effectiveness of the biological control research applied to forest pests.
For taxonomic and other reasons, many changes in the names of insects or the spelling
of insect names have taken place during the current review period. In order to standardize
sQme of these changes, forestry contributions follow the nomenclat.ure of insect pests
given in the "Common names of insects and related organisms" published by the
Entomological Society of America in 1980.
Inoculative releases of parasitoids and predators
When planning this strategy of biological control it has become customary to first
establish whether the target pest is a native or an introduced species. Of the 21 pests