ranges match with stimuli of foraging envi-
ronments is of vital importance in choosing
a strain for use as biological control agent in
a given environment.
For a population of parasitoids to be pre-
dictable and consistent in biological control,
it must have a proper blend of genetic traits
appropriate to the target environment and
those traits must occur sufficiently uniformly
in the population (Hoy, 1988). The need for a
proper match of the parasitoid population
with the target biological control environ-
ment has generally been recognized, but has
been dealt with only on a gross level in
applied programmes. For example, para-
sitoids colonized for a particular release situ-
ation have often been chosen from habitat
and host circumstances similar to that
expected in the targeted area (Caltagirone,
1985; Pak, 1988; Wajnberg and Hassan, 1994).
We expect that in the near future the colo-
nized parasitoids can at least be monitored
with DNA-fingerprinting techniques to
determine if their genetic make-up still
incorporates necessary behavioural and
other traits and if the important traits are
occurring uniformly in the colony (e.g. Silva
et al., 2000).
Phenotypic plasticityThe activated response potential (Fig. 4.1,
darkened area) of a foraging female is quite
plastic and can be modified within the
bounds of its genetic potential (Chapter 3;
Vet et al., 1990, 1995). The activated response
potential of a parasitoid at any given time is
dependent on the experience history of the
individual at that moment. As discussed ear-
lier, these modifications in response behav-
iour can begin during development as a
result of the parasitoid’s interaction with its
environment. Thus, the activated response
potential of the naïve adult will necessarily
be altered as a routine consequence of rear-
ing. The direction and level of the alteration
as a result of rearing will depend on, among
other things, the host species and host diet;
these alterations have seldom, if ever, been
quantified, although it has often been specu-
lated that such changes occur (Chapters 1
and 12). Subsequently, the activated response
potential of the adult parasitoid continues to
change as a result of the experiences during
foraging activities (see the earlier discussion
on within-individual plasticity).
A hypothetical example of the changes
in the activated response potential as a
result of experience is shown for genotype
G 1 in Fig. 4.1. As stated earlier, the geno-
typic response range of G 1 embraces the
various stimuli from the foraging environ-
ments EA, EB and EC, as indicated by the
length and alignment of its range. This
hypothetical individual could develop a
peak activated response potential for any of
the three environments by successful expe-
rience with stimuli of that environmental
situation (Vet, 1983; Wardle and Borden,
1985; Lewis and Tumlinson, 1988; Vet et al.,
1995). The highest activated response
potential can be developed for stimuli of its
more preferred environment, EB. Also, data
suggest that the activated response levels
for EB stimuli can be increased more
quickly. Absence of reinforcement will
result in a waning of the level of the acti-
vated response potential and a reversion to
its naïve preference for the cues of EB (see
Chapter 3 for a detailed discussion of mod-
ifications of parasitoid response potential).Physiological stateA parasitoid’s physiological state relative to
other needs, such as food, mating and gen-
eral health, can strongly influence the quality
of its foraging behaviour. For example, if a
female parasitoid is hungry, the appetitive
drive for food cues may take precedence
and, as a result, responses to host-related
cues may be reduced (Chapter 5; Hagen and
Bishop, 1979; Wäckers, 1994; Lewis et al.,
1998). Also, a lack of mature eggs in the
ovaries can reduce the response to olfactory
cues (Shahjahan, 1974). Further, the presence
of other strong chemical, visual or auditory
cues would probably disrupt the response to
host-foraging cues by dilution. In other
words, the physiological state of the para-
sitoid can greatly affect its propensity and
ability to respond to the host-selection cues.48 W.J. Lewiset al.