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al., 1997). The most commonly sold species
in Europe and North America are discussed
in this chapter (Table 11.2). These species are
divided into four groups: parasitoids, preda-
tory insects, predatory mites and ento-
mopathogenic nematodes. Most natural
enemies are used for biological control in
greenhouses, with the exception of Harmonia
sp. and Trichogrammaspp., which are also
used in the open field.

Parasitoids

Aphelinus abdominalisDalman

This parasitic wasp is used to control the
potato aphid Macrosiphum euphorbiae
(Thomas) and the greenhouse potato aphid
Aulacorthum solani Kaltenbach. It is sold in
units of 100 or 250 adults or pupae. Since A.
abdominalis does not easily spread over the
crop, it should be introduced where aphid
foci occur (Koppert, 1994). The recommended
rates for release range from two to four
wasps m^2 in the focal point of the infesta-
tion. Usually, A. abdominalisis used in combi-
nation with Aphidoletes aphidimyza Rondani.

Aphidius colemaniViereck

This species is a parasitoid of the cotton
aphid Aphis gossypiiGlover and the green
peach aphid Myzus persicaeSulzer. The rec-
ommended rate for release ranges from 0.15
m^2 for preventive introductions to 1.5 m^2
in heavily infected areas.

Aphidius ervi Halliday

This parasitoid is used to control the potato
aphid M. euphorbiae. The recommended
release rate ranges from 0.15 m^2 to 1 m^2.

Aphytis melinus DeBach

This species is sold for control of armoured
scales (e.g. California red scale, yellow scale,
and oleander scale). The suggested release

rates are in the order of five to 100 adults per

infested plant.

Dacnusa sibirica Telenga

This species is used to control leafminers

such as the tomato leafminer Liriomyza bry-

oniae(Kaltenbach), the American serpentine

leafminer Liriomyza trifolii(Burgess) and the

pea leafminer Liriomyza huidobrensis

(Blanchard). D. sibiricais supplied in units of

250 adults. This parasitoid is advised for use

mainly during the winter in northern Europe.

Diglyphus isea (Walker)

This parasitoid is also used for controlling

leafminers and it is sometimes sold with D.

sibiricain mixed culture. It is sold in units of

250 adults. The recommended introduction

rate (mostly mixed with D. sibirica) ranges

from 0.25 m^2 for preventative introductions

to 2 m^2 in heavily infested areas.

Encarsia formosaGahan

This is a parasitoid of the greenhouse white-

fly Trialeurodes vaporariorum(Westwood) and

the whiteflies Bemisia tabaci(Gennadius) and

Bemisia argentifoliiBellows and Perring, and

is one of the most remarkable examples of

the potential of a biological control agent

(van Lenteren et al., 1996). The small para-

sitoid was accidentally imported into Europe

• as was greenhouse whitefly – and was dis-
  covered as a parasitoid of whiteflies by
  Speyer (1927). Shortly after its discovery, it
  became very popular in the 1930s, both in
  Europe and elsewhere. After the second
  world war, its use declined because of the
  availability of broad-spectrum insecticides.
  Nowadays, E. formosa is one of the most used
  biological control agents in protected crops,
  and also the most important natural enemy
  when expressed in monetary value for pro-
  ducers (van Lenteren, 1995; Bolckmans,
  1999). E. formosa is produced in enormous
  numbers. The annual production by large
  companies is about half a billion parasitoids.

172 J.C. van Lenteren