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onwards. It should not be delayed until
problems occur. Introducing field-collected
insects into mass rearing also poses risks of
introduction of parasitoids, predators or
pathogens into the colony (Bartlett, 1984b).
Another effect of laboratory colonization
can be inbreeding – mating of relatives and
production of progeny that are more geneti-
cally homozygous than when random mat-
ing occurs in large populations. Genetically
homozygous individuals often expose harm-
ful traits. The degree of inbreeding is directly
related to the size of the founder population.
Because artificial selection in the laboratory
often results in an initial decrease in popula-
tion size, the rate of inbreeding increases.
The result is often a definite and rapid effect
on the genetic composition of the laboratory
population (Bartlett, 1984b). Inbreeding can
be prevented by various methods that main-
tain genetic variability (Joslyn, 1984), includ-
ing the following:

1.Precolonization methods: selection and
pooling of founder insects from throughout
the range of the species to provide a wide
representation of the gene pool, resulting in
a greater fitness of the laboratory material.
2.Postcolonization methods:
a. Variable laboratory environments
(variation over time and space). Although
the concept of varying laboratory condi-
tions is simple, putting it into practice is
difficult. Consider for example the invest-
ments for rearing facilities with varying
temperatures, humidities and light

regimes, or the creation of possibilities to

choose from various diets or hosts, or the

provision of space for dispersal, etc.

b. Gene infusion: the regular rejuvenation

of the gene pool with wild insects.

A fundamental question concerning inbreed-

ing is: how large must the population size be

to keep genetic variation sufficiently large?

Joslyn (1984) says that, to maintain sufficient

heterogeneity, a colony should not decline

below the number of founder insects. The

larger the colony, the better. Very few data

are available about effective population size;

Joslyn (1984) mentions a minimum number

of 500 individuals.

The above discussion suggests several cri-

teria to be considered before a mass-rearing

colony is started (Table 1.3, after Bartlett,

1984b).

A broader approach to quality control

Chambers and Ashley (1984), Leppla and

Fisher (1989) and Leppla (Chapter 2) put

quality control in a much wider perspective.

These papers are food for thought for all

engaged in mass production of beneficial

arthropods. They present some refreshing

and, for most entomologists, new ideas.

These authors approach quality control from

the industrial side and consider three ele-

ments as essential: product control, process

control and production control. Product con-

trol rejects faulty products and production

10 J.C. van Lenteren

Table 1.3. Criteria to be considered before starting a mass-rearing programme.

1.The effective number of parents at the start of a mass rearing is much lower than the

number of founder individuals, so start with a large population

2.Compensate for density-dependent phenomena

3.Create a proper balance of competition, but avoid overcrowding

4.Set environmental conditions for the best, not the worst or average, genotype; use

fluctuating abiotic conditions

5.Maintain separate laboratory strains and cross them systematically to increase F 1

variability

6.Measure frequencies of biochemical and morphological markers in founder populations

and monitor changes

7.Develop morphological and biochemical genetic markers for population studies

8.Determine the standards that apply to the intended use of the insects, and then adapt

rearing procedures to maximize those values in the domesticated strain