recognize and respond effectively to this
diversity as a resource rather than an obsta-
cle to pest-management science.
Breeders of domesticated plants and ani-
mals have long recognized and exploited
genetic diversity for useful purposes.
However, most augmentative biological con-
trol programmes with parasitoids differ from
conventional animal-breeding and produc-
tion programmes in that the parasitoids are
cultured and maintained in laboratory insec-
taries apart from the natural environment
where they must eventually perform (see
Chapters 1, 11 and 12). Therefore, it will be
necessary for us to use techniques to ensure
that the genotypic and phenotypic traits
important to their performance in the natural
environment are maintained intact and even
enhanced during insectary production. The
development and incorporation of such tech-
nology into biological control will necessitate
understanding the sources and functional
mechanisms of variations in parasitoid for-
aging behaviour. The result will be to
enhance the quality of natural enemies and
to improve their performance in the field.
Waage and Hassell (1982), citing van
Lenteren (1980) and various case-history
reports, stated:
perhaps the outstanding question in biological
control today is whether the use of parasitoids
is to remain such an art, aided largely by the
knowledge of what worked last time or
whether it has the potential to become a fully
predictive science, aided by fundamental
research and theory.Sources of Intraspecific Variations in
Foraging Behaviour
Numerous extrinsic factors, such as climatic
conditions and host density, can affect forag-
ing behaviour (Chapter 1). However, in this
chapter we are concerned primarily with
intrinsic sources of variation. Adaptive varia-
tions in foraging traits are necessary for a
parasitoid species to deal with different for-
aging environments. As reported for other
organisms (Bradshaw, 1965; Papaj and
Rausher, 1987; Papaj and Prokopy, 1989),
there are two alternative types of adaptive
variation in the foraging behaviour of a para-
sitoid species. One type of intraspecific vari-
ation is caused by genetically fixed
differences among individuals. In this case, a
species may have various genotypes that
have a fixed or ‘hard-wired’ behaviour that
inherently adapts them for operating effec-
tively under the respective conditions for
which they have been selected. For example,
if the host occupies several habitats, the par-
asitoid species may consist of strains with
different capabilities for searching in each of
the habitats (Boulétreau, 1986; Pak, 1988;
Wajnberg and Hassan, 1994).
This genotypic diversity among individu-
als of a species has generally been recog-
nized by scientists and to some extent has
been incorporated into considerations for
biological control (Caltagirone, 1985; Luck
and Uygun, 1986; Wajnberg and Hassan,
1994).The fact that strains of parasitoids that
occupy different regions with different cli-
matic conditions are inherently more suited
for their respective ecological conditions has
been well documented and appreciated (e.g.
Pak, 1988). Also, populations of a parasitoid
species with long-standing associations with
different hosts and habitats are known to
differ in their affinity and behaviour relative
to those host-habitat situations (e.g.
Mollema, 1988; Pak, 1988). In addition to
these discrete genetic differences that occur
among populations, we have more recently
documented subtle, but distinct and mea-
surable, heritable differences in the behav-
iour patterns of individuals within a single
interbreeding population (Prévost and
Lewis, 1990). These within-population dif-
ferences are perhaps preserved as a result of
the continuing flux of circumstances that the
population encounters.
A second type of intraspecific variation is
within individual plasticity (phenotypic
plasticity, sensuRoughgarden (1979)). In this
type the individuals have a partly open or
unfixed behaviour (plastic within certain
limits). These individuals are capable of
adapting by experience for foraging more
effectively in any one of a variety of circum-
stances that may be encountered. For exam-
ple, a parasitoid of hosts that occurs inVariations in Foraging Behaviour 43