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cinnabarinus (Boisduval) can also be controlled
with this predator. This predatory mite is often
mixed with vermiculite and put in shaker bot-
tles. They need to be sprinkled on the leaves.
Extra predatory mites should be placed in spi-
der-mite hot spots (Koppert, 1994). For opti-
mal development of the predator population,
the relative humidity should not be under 75%
and the temperature needs to be regularly
above 20°C. P. persimilisis supplied in units of
1000 or 2000 mites, although a few producers
offer a smaller quantity of 100 or 250 mites.

Entomopathogenic Nematodes

Members of the families of Steinernematidae
and Heterorhabditidae are important ento-
mopathogenic nematodes of scarabaeid larvae
or lepidopteran caterpillars in soil. Desirable
assets, such as ease of mass production, effi-
cacy and safety for non-target organisms, have
evoked commercial interest in these nema-
todes (Parwinder and Georgis, 1994). The
nematodes kill their host by releasing symbi-
otic bacteria (Xenorhabdusspp.), which are car-
ried in their alimentary tract. These bacteria
multiply rapidly inside the insect’s
haemolymph and kill their host within 48 h.
The symbiotic bacteria convert host tissue into
products that can easily be taken up by the
nematodes. Inside the beetle cadaver, the
nematodes reproduce. As soon as the nema-
todes reach the infectious third-juvenile stage,
they leave the old host and start searching for
new weevil larvae. Usually billions of nema-
todes should be released per hectare.

Steinernema carpocapsaeWeiser

This is the most widely available ento-
mopathogenic nematode and is easy to rear,
store and handle. It is sold to control a wide
range of insects.

Steinernema feltiae(Filipjev)

This species is an entomopathogen of
Sciaridae, but other target pests are also
under investigation. This entomopathogenic

nematode infects larval/nymphal, prepupal

and pupal stages of insects that spend (part)

of their life cycle in the soil (Tomalak, 1994),

so they may be used for controlling thrips

and leafminers.

Heterorhabditis megidesPoinar

This nematode is used for control of the vine

weevil Otiorhynchus sulcatus(F.). One pro-

ducer supplies the nematodes, together with

inert carrying material, in a 250 ml package,

containing 50 million nematodes. This

should be sufficient for 100 m^2 (for a blanket

treatment) or for 10 m^3 soil (Koppert, 1994).

Entomopathogenic Fungi, Bacteria

and Viruses

Currently, a number of entomopathogenic

fungi, bacteria and viruses are on the market

and can be used for control of pests. Because

of their special character, way of production

and application compared with the ‘macrobi-

ological’ control agents, such as predators

and parasitoids, they are not treated in detail

here. To date, there are five nucleopolyhe-

droviruses (NPViruses), five Bacillus

species/strains and ten species of fungi

available for insect control in greenhouses

(Lipa and Smits, 1999). For a review of these

microbial natural enemies, refer to Lipa and

Smits (1999).

Discussion and Conclusions

One way to express the importance of the dif-

ferent categories of natural enemies is by speci-

fying the surface area on which they are

applied. Although this is not an easy task (see

Chapter 1 and van Lenteren, 2000), the roughly

estimated areas under augmentative forms of

biological control are given in Fig. 11.1.

The relative importance of the different

natural enemies can be also expressed by

their monetary value. Reliable data are avail-

able for biological control agents used in

greenhouses (Bolckmans, 1999), but are lack-

ing for field applications, although it is esti-

176 J.C. van Lenteren