0851996884.pdf

quality of the population. The overall quality
of an organism can be defined as the ability
to function as intended after release into the
field. The aim of quality control programmes
is to check whether the overall quality of a
species is maintained, but that is too general
a statement to be manageable. Charac-
teristics that affect overall quality have to be
identified. These characteristics must be
quantifiable and relevant for the field perfor-
mance of the parasitoid or predator. This is a
straightforward statement, but very difficult
to actually put into practice (Bigler, 1989).
Rather than discussing the development
of quality control in strictly scientific terms,
this discussion will outline a more prag-
matic approach. The aim of releases of mass-
produced natural enemies is to control a
pest. In this context, the aim of quality con-
trol should be to determine whether a nat-
ural enemy is still in a condition to properly
control the pest. Formulated in this way, we
do not need to consider terms like maximal
or optimal quality, but rather acceptable
quality. Some researchers believe the aim of
quality control should be to keep the quality
of the mass-reared population identical to
that of the original field population. Not
only is this an illusion (see Chapters 6 and
7), but it is also an unnecessary and expen-
sive goal to pursue. Another important con-
sideration is that quality control
programmes are not applied for the sake of
the scientist, but as a necessity. Leppla and
Fisher (1989) formulated this dilemma as:
‘Information is expensive, so it is important
to separate “need to know” from “nice to
know”.’ Only if characteristics to be mea-
sured are very limited in number, but
directly linked to field performance, will
companies producing natural enemies ever
be able to apply quality control programmes
on a regular basis.

Basic Considerations for Quality Control

Genetic changes in laboratory colonies

The problem of quality control of beneficial
insects can be approached from two sides:

1.Measure how well the biological control

agent functions in its intended role. If it does

not function well enough, trace the cause

and improve the rearing method.

2.List what changes we can expect when a

mass rearing is started; measure these and, if

the changes are undesirable, improve the

rearing method.

The disadvantage of the first method is that

changes may have occurred that cannot be

corrected because the material has already

changed so much that the original causes of

the observed effects cannot be identified. The

disadvantage of the second method is that

too many measurements may be needed.

The second approach has the advantage that

potential problems are foreseeable and cor-

rections can be made in time. Bartlett

(1984a), for example, approaches the prob-

lem from the second viewpoint. He states

that many authors have suggested remedial

measures for assumed genetic deterioration,

but that causes for deterioration are not eas-

ily identified. Identification demands

detailed genetic studies, and it is often diffi-

cult to define and measure detrimental

genetic traits. Bartlett (1984a) concludes:

I believe an unappreciated element of this

problem is that the genetic changes taking

place when an insect colony is started are

natural ones that occur whenever any

biological organism goes from one

environment to another. These processes have

been very well studied as evolutionary events

and involve such concepts as colonisation,

selection, genetic drift, effective population

numbers, migration, genetic revolutions, and

domestication theory.

In two other articles, Bartlett (1984b, 1985)

discusses what happens to genetic variability

in the process of domestication, what factors

might change variability and which ones

might be expected to have little or no effect.

In laboratory domestication, those insects are

selected that have suitable genotypes to sur-

vive in this new environment, a process

called winnowing by Spurway (1955) or, less

appropriately but widely used, ‘forcing

insects through a bottleneck’ (e.g. Boller,

1979). The changes that a field population

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