The tests should be representative of the
climatic, habitat (e.g. host-plant species, age
and parts) and host-insect (e.g. age, density
and distribution) situations that the para-
sitoid will encounter under field situations
and be adequate for evaluating their ability
to perform the full sequence of host-selection
behaviours in those situations (Chapters 16
and 17). A good balance is needed between
enough genetic diversity to cope with the
fluctuations they will encounter and unifor-
mity in the amount of diversity for consis-
tency (Chapters 6 and 7). However, the
amount of diversity desired may vary among
the different traits. Similar testing techniques
to monitor the colony systematically are
needed for preservation of the diversity and
uniformity of these traits (Chapters 1, 2, 15
and 16). Prévost and Lewis (1990) provide an
example of how a flight chamber can be used
to assess various genetic variations in host-
finding response traits and how they can be
measured and compared over generations for
different colony lines.
Phenotypic qualities – learningThe response potential of a parasitoid is
often a result of experiences in the preadult
and adult stages: without care, insectary
environments can create either weak or dis-
torted response profiles (Chapters 1, 2 and
19). However, by understanding the sources
and mechanisms of learning, we can provide
the appropriate level of experience. As dis-
cussed earlier, the lack of important semio-
chemicals in the host-insect diet and use of
factitious host insects have been shown to
cause poorly responsive parasitoids. These
semiochemicals can be incorporated artifi-
cially into the diet and on the hosts as syn-
thetics or as materials such as plant extracts.
This approach may be particularly important
in some cases where important learning
experiences occur in the immature or early
adult stages (Wardle and Borden, 1985;
Hérard et al., 1988b; van Emden et al., 1996).
Another approach that has been the sub-
ject of some experimentation is the prerelease
exposure of the adult to important stimuli.
Gross et al. (1975) showed that, with
Microplitis croceipes (Cresson) and
Trichogramma pretiosum Riley, exposure to host
frass or host-moth scales increased the pro-
portion of parasitism in the release area and
attributed the benefit primarily to a reduction
in the escape response upon emergence from
the release container. Subsequent studies dis-
cussed earlier in this and the previous chapter
have shown that prerelease exposure of the
parasitoid to the kind of host and associated
stimuli situations that they will encounter in
the field can result in associative learning that
enhances the parasitoids’ subsequent ability
to perform at the time of release.
There are genetic variations among indi-
viduals of a species as to what can be learned
and to what degree. These variations are an
important consideration for both the geno-
typic and phenotypic qualities of parasitoids.Physical and physiological qualities
In addition to the constraints placed on
learning experiences, the unnatural insectary
environment can be stressful to the physical
and physiological well-being of parasitoids
(Chapter 1). For example, insect movements
are restricted and the unnatural lighting,
temperature and humidity may affect the
females in a way that subsequently alters
foraging behaviour. P.O. Zanen and W.J.
Lewis (unpublished data) found that chilling
the cocoons of M. croceipes severely reduced
the ability of females to make flight
responses to volatile host odours. Sublethal
diseases (Chapter 10) that are not readily
apparent may spread in the colony and affect
behaviour. Hamm et al.(1988) reported a
viral infection in an M. croceipes colony that
accounted for reduced host-finding
responses in flight chambers. Further, mating
and nutritional conditions can strongly affect
foraging responses (Chapter 5).
As is apparent from these points, the physi-
cal and physiological needs are very impor-
tant to effective foraging behaviour. Because
neither weaknesses in the learning conditions
nor those of the physical or physiological state
may be readily apparent from general obser-
vation, various response-evaluation tech-
niques, such as those discussed for the
genotypic traits, should be used to monitor the
quality of the phenotypic traits of the colony.52 W.J. Lewiset al.