particularly relevant for parasite infective stages, which often search for
hosts that are larger and more mobile, e.g. parasitic nematodes (Rogers
and Sommerville, 1963; Hernandez and Sukhdeo, 1995) and trematodes
of vertebrates (Combeset al., 1994), arthropod ectoparasites (Lees and
Milne, 1950) and insect-parasitic nematodes (Campbell and Gaugler,
1993).
The adoption of a particular foraging mode influences a range of
related characters, forming what has been termed an adaptive syndrome
(Root and Chaplin, 1976). Under this perspective, species that are
distantly related taxonomically may share similar adaptive syndromes
due to similarity in foraging mode (Eckhardt, 1979). For example, some
postulated correlates of foraging mode have been developed for lizards
(Huey and Pianka, 1981). These include that ambush foragers should eat
mobile prey, capture few prey per day and have a low daily metabolic
expenditure, a low probability of encountering prey, limited endurance,
limited learning ability and stocky morphology and use primarily visual
cues. Cruise foragers are predicted to eat sedentary and unpredictable
prey that are clumped or large, capture high numbers of prey per day and
have a high daily metabolic expenditure, a high probability of encounter-
ing prey, a high endurance capacity, enhanced learning and memory and
streamlined morphology and use visual and chemical cues. Clearly, many
of these characters may not apply to parasite infective-stage foragers,
but the idea that there may be adaptive syndromes associated with the
way that parasites search is a fruitful area for research. The presence of
adaptive syndromes means that assigning a forager to a particular category
provides insight into aspects of an organism’s biology other than just host
search.
Foragers typically respond behaviourally to stimuli from the environ-
ment in ways that improve the probability or rate of encounter with a
resource. The method of scanning, the relative importance of different
stimuli and the nature of the response will be influenced by foraging
strategy (O’Brienet al., 1989, 1990). Many foragers use multiple sensory
modalities and cues (e.g. mechanical, chemical or auditory) during search
and their relative importance may depend on foraging strategy. Research
into behavioural mechanisms has been heavily biased toward the more
active cruise foragers – for example, the use of chemotaxis and localized
search patterns in patches to facilitate finding resources (e.g. Bell, 1985;
Huettel, 1986; Ramaswamy, 1988; Vet and Dicke, 1992). However, stimuli
from the environment have also been demonstrated to be important for
ambush foragers. Cues are used for selecting ambush sites (Greco and
Kevan, 1994, 1995), assessing patch quality (O’Brienet al., 1990; Sonerud,
1992) and triggering resource-capture behaviours (Bye et al., 1992).
Foragers may be able to improve their foraging efficiency by adjusting
their allocation of time to pausing and moving in response to external
stimuli (i.e. shift along the continuum between ambush and cruise
foraging) (O’Brienet al., 1990). This ability has been demonstrated for a
number of species of insects, fish, birds and lizards (Akre and Johnson,Entomopathogenic Nematode Host-search Strategies 15