3 A Variable-response Model for Parasitoid
Foraging Behaviour
L.E.M. Vet,1,2W.J. Lewis,^3 D.R. Papaj^4 and J.C. van Lenteren^1
(^1) Laboratory of Entomology, Wageningen University, PO Box 8031, 6700 EH
Wageningen, The Netherlands;^2 Netherlands Institute of Ecology, PO Box 40,
6666 ZG Heteren, The Netherlands;^3 Insect Biology and Population Management
Research Laboratory, USDA-ARS, PO Box 748, Tifton, GA 31793, USA;^4 Department
of Ecology and Evolutionary Biology, University of Arizona, Tucson, AZ 85721, USA
Introduction
Much information has become available on
cues utilized by parasitoids during foraging
for hosts or food over the past decade
(Chapters 4 and 5; Vet and Dicke, 1992;
Godfray, 1994; Wäckers, 1994; Vet et al., 1995;
Lewis et al., 1998; Powell, 1999). At the same
time, it became clear that foraging behaviour
could no longer be considered to be fixed
and predictable, but rather it varies in
response to the insect’s physiological condi-
tion and genetic composition as well as to
environmental factors. However, the quest
for factors inducing variability in parasitoid
foraging behaviour has largely centred on
the influence of learning. Experience in
either preadult or adult stages modifies adult© CAB International 2003. Quality Control and Production of Biological Control Agents:
Theory and Testing Procedures (ed. J.C. van Lenteren) 25
Abstract
An important factor inducing variability in foraging behaviour in parasitic wasps is experience gained by
the insect. Together with the insect’s genetic constitution and physiological state, experience ultimately
defines the behavioural repertoire under specified environmental circumstances. A conceptual variable-
response model based on several major observations of a foraging parasitoid’s responses to stimuli
involved in the host-finding process is presented in this chapter. These major observations are that: (i) dif-
ferent stimuli evoke different responses or levels of response; (ii) strong responses are less variable than
weak ones; (iii) learning can change response levels; (iv) learning increases originally low responses more
than originally high responses; and (v) host-derived stimuli serve as rewards in associative learning of
other stimuli. The model specifies how the intrinsic variability of a response will depend on the magni-
tude of the response and predicts when and how learning will modify the insect’s behaviour. Additional
hypotheses related to the model concern how experience with a stimulus modifies behavioural responses
to other stimuli, how animals respond in multi-stimulus situations, which stimuli act to reinforce behav-
ioural responses to other stimuli in the learning process and, finally, how generalist and specialist species
differ in their behavioural plasticity. It is postulated that insight into behavioural variability in the foraging
behaviour of natural enemies may be a help, if not a prerequisite, for the efficient application of natural
enemies in pest management and for developing quality control tests of biocontrol agents.