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both herbivores and their natural enemies,
and these natural enemies are a substantial
component of biodiversity. The search
behaviour of natural enemies generally
leads to the decision to leave host patches
before parasitizing or eating all hosts or
prey. Further, hosts have mechanisms of
escaping their natural enemies in space and
time, which reduce the chances of the host
becoming extinct. Ecologists have long rec-
ognized the role that predators, parasitoids
and pathogens play in reducing popula-
tions of plant-feeding organisms (herbi-
vores – in agroecosystems, often pest
insects), thereby ‘keeping the world green’
(e.g. Crawley, 1992).
In this section on direct effects, first test-
ing for host specificity – the focal point of
any environmental risk assessment – was
described, followed by other direct effects,
such as intraguild predation, competition
and displacement, hybridization, effects on
plants and risk of vectoring diseases below.

Intraguild predation

The occurrence of intraguild predation,
which is the killing and eating of species that
otherwise use similar resources (Rosenheim
et al., 1995; Brodeur and Rosenheim, 2001),
can be checked in the literature. If intraguild
predation effects are indicated for the spe-
cific or for related natural-enemy species or
can be concluded from the biology of the
natural enemy, then intraguild predation
should be investigated case by case.
Qualitative and quantitative effects should
be listed and resulting effects estimated (pos-
itive, neutral or negative). Finally, a conclu-
sion concerning risk should be drawn.

Competition and displacement

Check the literature if competition and dis-
placement effects are indicated for the spe-
cific or related natural-enemy species or
conclude from the biology of the natural
enemy if effects are expected. Then investi-
gate case by case. List qualitative and quanti-
tative effects and estimate effects (positive,
neutral or negative). Finally, draw a conclu-
sion concerning risk.

Hybridization

Estimate or determine the likelihood of

hybridization between the natural enemy

and indigenous strains or biotypes of the

same or very closely related natural-enemy

species, discuss potential effects and draw a

conclusion concerning risk.

Effects on plants

Effects of the natural enemy on plants

should be provided if the agent is potentially

a facultative herbivore. Check the literature

if effects on target crop and non-target plants

are indicated for the specific or related nat-

ural-enemy species or conclude from the

biology of the natural enemy if effects are

expected. Then investigate case by case. List

qualitative and quantitative effects and draw

a conclusion concerning risk.

Risk of vectoring diseases

Check the literature if vectoring of viruses or

microorganisms that can negatively affect

non-target organisms is indicated for the spe-

cific or related natural-enemy species (Chapter

10). Draw a conclusion concerning risk.

Indirect effects of released organism

An indirect effect of releases may be a

reduction in the numbers of endemic nat-

ural enemies as a result of: (i) a strong

reduction of their prey or host that is the

target pest, which is attacked by the intro-

duced natural enemy; and/or (ii) competi-

tion with endemic natural enemies for other

hosts or prey of the introduced natural

enemy. Further, the habitat may be modified

as a result of indirect interactions. It has

been suggested that, in some cases, releases

of polyphagous predators has not only led

to a decimation of pest caterpillars but also

to a reduction of non-target caterpillars,

resulting in a decline in native predacious

wasps and native bird populations

(Simberloff, 1992). Myriad indirect effects

are possible. Species can interact through

shared prey or hosts or shared predators,

Regulation and Risk Assessment of Biocontrol Agents 199