cruise foraging a nematode infective stage lies. Most nematode species
crawl by sinusoidal movement on the substrate, using the surface-tension
forces associated with the water film to propel them forwards or back-
wards (Croll, 1970). Nematodes perceive their environment primarily
by chemosensation, thermosensation and mechanosensation. How envi-
ronmental cues such as chemical and temperature gradients influence
crawling nematodes has been the most extensively studied area of
nematode behaviour (Croll, 1970; Dusenberry, 1980; Zuckerman and
Jansson, 1984; Huettel, 1986; Bargmann and Mori, 1997). Crawling
nematodes may scan for environmental cues while crawling on the
substrate or during short pauses. Crawling locomotion and the use of
various kineses and taxes to locate hosts is consistent with a cruise type
of foraging strategy.
The infective stages of some entomopathogenic nematode species
exhibit two additional behaviours that facilitate ambush foraging:
standing and jumping. Most nematodes can raise the anterior portion of
their body off the substrate and wave it back and forth. However, some
species can elevate more than 95% of their body off the substrate and
balance on a bend in their tail (Reed and Wallace, 1965; Ishibashi and
Kondo, 1990; Campbell and Gaugler, 1993). This behaviour has been
termed ‘Winken’ (Völk, 1950), ‘nictation’ (Ishibashi and Kondo, 1990;
Campbell and Gaugler, 1993) and most recently ‘standing’ (Campbell and
Kaya, 1999a,b, 2000). Standing behaviour is restricted to the free-living
infective or dauer stages of certain species (Campbell and Gaugler, 1993;
1997; Campbell and Kaya, 2002). Among species that exhibit standing
behaviour, variation occurs in the duration of standing bouts and
nematode activity while standing. Some species have a stable standing
behaviour, in which the nematode becomes straight and immobile and
can maintain this posture, with interspersed periods of waving, for
extended periods of time (can exceed 2 h). Standing behaviour facilitates
attachment to mobile hosts by reducing the surface tension holding the
nematode to the substrate (Campbell and Gaugler, 1993). Standing bouts
are ended by the nematode falling, by touching the anterior portion of its
body to a surface during waving or by jumping. Standing behaviour may
function as both an immobile scanning bout and a mechanism to attack
passing hosts.
Jumps occur when an infective juvenile is standing; the nematode
forms a loop with its body, which, when released, propels the nematode
many times its body length through the air (Reed and Wallace, 1965;
Campbell and Kaya, 1999a,b, 2000). The forces generated bySteinernema
carpocapsae’s jumping mechanism propel individuals an average
distance of 4.8±0.8 mm (nine times the nematode’s body length) and an
average height of 3.9±0.1 mm (seven times body length) (Campbell and
Kaya, 1999a,b). The frequency of jumping, like standing behaviour, varies
among species ofSteinernema, but jumping has not been observed in
Heterorhabditis(Campbell and Kaya, 2002). Jumping can function as a
means of dispersal and also as an ambush attack mechanism.Entomopathogenic Nematode Host-search Strategies 19