Two forms of periodic releases with nat-
ural enemies are generally distinguished: the
inundative and the seasonal inoculative
method. The inundative-release method is
where beneficial organisms are collected,
mass-reared and periodically released in
large numbers to obtain immediate control
of a pest (i.e. use as a biotic insecticide). Pest
control is mainly obtained from the released
natural enemies and not from their offspring.
Inundative releases are applied to crops
where viable breeding populations of the
natural enemy are not possible, in crops
where the damage threshold is very low and
rapid control is required at very early stages
of infestation or in crops where only one
generation of the pest insects occurs. An
example is the use of Trichogramma spp.
against the cornborer in maize in Europe
(Bigler, 1994). The seasonal inoculative-
release method is where natural enemies are
collected, mass-reared and periodically
released into short-term crops (6–12 months)
and where many pest generations occur. A
relatively large number of natural enemies is
released to obtain both immediate control
and a build-up of the natural-enemy popula-
tion for control throughout the same grow-
ing season. This method can be applied
when the growing method of a crop prevents
control extending over many years – for
example, in greenhouses where the crop
together with the pests and natural enemies
are removed at the end of the growing sea-
son. The method is distinctly different from
the inundative method and more closely
resembles the inoculative or classical biocon-
trol method because control is obtained for a
number of generations of the pest and con-
trol would be permanent if the crop were
grown for a much longer period. The sea-
sonal inoculative-release method has been
developed in Europe during the last three
decades and is applied with great commer-
cial success in greenhouses. Two well-known
natural enemies used in this approach are
the spider-mite predator Phytoseiulus persim-
ilisand the whitefly parasitoid Encarsia for-
mosa(van Lenteren, 1995).
Augmentative biological control is
applied worldwide. Data about the current
use of augmentation are sometimes very
hard to obtain (e.g. for Russia) and estimates
are therefore incomplete. A worldwide
review from 1977 (Ridgway and Vinson,
1977) provides data about the use of natural
enemies in the USSR (on 10 million ha),
China (1 million ha), West Europe (< 30,
ha) and North America (< 15,000 ha). Since
that review, many new natural enemies have
become available (Anon., 2000) and activities
have strongly increased in Latin America
(van Lenteren and Bueno, 2002). The best-
known examples of augmentative biological
control are those: (i) where the egg parasitoid
Trichogramma is used for control of
Lepidoptera in various crops (Smith, 1996);
and (ii) where a whole set of different nat-
ural enemies (parasitoids, pathogens and
predators) is used to manage pests in green-
houses (Albajes et al., 1999). The total world
area under augmentative biological control
was recently estimated to be about 16 million
ha (van Lenteren, 2000a).
For a long time, natural enemies were
produced without proper quality control
procedures. Poorly performing natural ene-
mies resulted in failures of biological control
and a low profile of this pest-control method
(e.g. P. DeBach, Riverside, California, 1976,
and P. Koppert, Berkel and Rodenrijs, The
Netherlands, 1980, personal communica-
tions). Quality control was touched upon by
several biological control workers in the 20th
century, but the first papers seriously
addressing the problem appeared only in the
1980s (van Lenteren, 1986a).Emergence of Quality Control
Trends in commercial mass production of
natural enemiesThe appearance and disappearance of nat-
ural-enemy producers have characterized
commercialization of natural enemies over
the past 30 years. Only a few producers
active in the 1970s are still in business today.
In addition to many small insectaries pro-
ducing at the ‘cottage-industry’ level, three
large facilities (i.e. having more than 50 per-
sons employed) exist that provide material
of good quality. At these three production2 J.C. van Lenteren