from the findings that artificial faecal pellets
containing the reinforcing host-recognition
kairomone and desired volatile odours can
be applied to a crop at a sufficient density to
reinforce search that is focused towards
those volatiles. By using volatiles more
prevalent in certain parts of the plant, the
elicited search behaviour can be concen-
trated on certain portions of the plants or in
other ways directed as desired. It is
expected that similar phenomena and thus
manipulation prospects exist for other para-
sitoid species.
Conclusions
There are three major sources of intrinsic
variations in the foraging behaviour of indi-
viduals of a parasitoid species. One source is
genotypically fixed differences among indi-
viduals that are adapted for different forag-
ing environments. Another source is the
phenotypic plasticity of individuals that
allows them to modify their behaviour
through learning to suit them for different
host-habitat situations. A third source is the
parasitoids’ physiological state relative to
other needs, such as food and mating.
The parasitoids’ effectiveness at locating
and attacking hosts is determined by the net
combination of these factors, together with
the conditions of their foraging environ-
ment. Therefore, our ability to obtain consis-
tent and effective biological control with
parasitoids can be strongly affected by our
understanding of the mechanisms govern-
ing these sources of variation and the devel-
opment of quality control techniques to
manage them.
With an appropriate knowledge of these
aspects of foraging behaviour, we can estab-
lish and ultimately engineer parasitoid
colonies with the best genotypic qualities for
their intended application. Further, we can
rear, handle and release the colonies in ways
that mould their phenotypic traits for opti-
mum results, and we can manage the target
environment to maximize parasitism by the
released and naturally occurring para-
sitoids. Without such information, we are
operating in a black box, in which the
proper design of biological control pro-
grammes and the interpretations of their
outcomes are a matter of speculation.
Many of the ideas expressed in this chap-
ter can also be applied to the management of
populations of predatory insects and mites,
but, as yet, insight in foraging behaviour of
predators is more limited than that of para-
sitoids (Steidle and van Loon, 2002).Acknowledgements
This chapter is the result of a cooperative pro-
gramme among the Insect Biology and
Population Management Research Laboratory
(US Department of Agriculture (USDA),
Tifton, USA), the Insect Attractants, Basic
Biology and Behaviour Research Laboratory
(USDA, Gainesville, USA) and the Laboratory
of Entomology, Wageningen University
(Wageningen, The Netherlands). The journal
Environmental Entomology (Entomological
Society of America) granted permission to
reprint an edited version of the original
Lewis et al. (1990) paper with the same title
and authors. Editing was made particularly
easy with the recent extensive critical
review of the 1990 paper by Steidle and
Van Loon (2002).54 W.J. Lewiset al.
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