0851996884.pdf

food and mating requirements and its gen-
eral health can vary because of diseases and
climatic conditions. The resulting physiologi-
cal state of the parasitoid interacts with the
genotypic and phenotypic foraging traits
discussed earlier in determining how a para-
sitoid will respond to a foraging environ-
ment (Chapter 5; Shahjahan, 1974; Hagen
and Bishop, 1979; Hamm et al., 1988;
Wäckers, 1994).

Model of the Factors Determining

Eventual Foraging Behaviour

The sources of variation discussed above are
not mutually exclusive; rather, they overlap
extensively, even within a single individual.
Therefore, it is important that we have a
means of clearly delineating the sources,
roles and interacting effects of the variations.
Our conceptual model for collectively
describing the various foregoing factors and
the sum of their effect on the foraging behav-
iour of parasitoids is presented in Fig. 4.1.
The three major sources of intrinsic variabil-
ity in the behaviour of foraging female para-
sitoids are represented: (i) genetic diversity
among individuals; (ii) phenotypic plasticity
within individuals because of experience;
and (iii) the parasitoid’s physiological state
relative to other needs. The behaviour mani-
fested is also dependent on the foraging
environment, so the final foraging effective-
ness of a parasitoid is determined by how
well the parasitoid’s net intrinsic condition
as a result of these three components is
matched with the foraging environment in
which it operates.

Genetic diversity

In Fig. 4.1, we present a hypothetical para-
sitoid species and three foraging environ-
ments: EA, EB and EC. Under the ‘genotypic
diversity’ heading, we show the response
potential for two representative individual
genotypes, G 1 and G 2. This response poten-
tial consists of the genetically fixed maxi-
mum range of usable foraging stimuli and
the ultimate level with which the parasitoid

could respond to the stimuli (the total dark-

ened area plus the shaded area). This maxi-

mum level of response to the array of stimuli

is shown as a curve, which indicates that the

maximum response level varies with differ-

ent stimuli in its range (Vet, 1983; Drost et al.,

1988; Vet et al., 1995). As reflected by the dif-

ferent range and curve configurations for G 1

and G 2 , the response potential may vary sub-

stantially among individuals within a popu-

lation (Hoy, 1988; Prévost and Lewis, 1990).

The activated response potential of G 1

and G 2 (darkened area) that could be real-

ized at any given time is somewhat less than

their overall potential and depends on the

experience of the individual, as documented

earlier and as will be further discussed

below for the model. Thus, only the

response potential activated at the time an

individual encounters stimuli can be mani-

fested. The balance of the response potential

that is not currently activated due to the

experience of the individual is the latent

response potential (shaded area). In the case

of naïve individuals, the active response

potential is that portion that is inherently

activated and thus does not require experi-

ence before it can be manifested.

Obviously, the response potential of the

individuals determines the response poten-

tial of a population that they make up, and

the populations in turn determine the

response potential of the species. However,

only the response-range parameter is shown

for the populations and species in Fig. 4.1,

because the response level would depend on

the density as well as the genotypes of indi-

viduals making up the population and

species at any given time. Horizontal align-

ment of the response-range lines in Fig. 4.1

with the representative environments

reflects the capacity to respond to the stim-

uli from that environment. As shown in Fig.

4.1, the stimuli of the three representative

foraging environments, EA, EB and EC, are

all within the range of population P 1 ; fur-

thermore, the response ranges of individuals

with the representative genotype, G 1 , are

best aligned with these environments.

However, the inherent preference of the

genotype G 1 , as indicated, is for environ-

ment EB. Information on how well response

46 W.J. Lewiset al.