cutting cycle (body immobilization and rhythmic stylet thrusting to cut
a slit in the cell against which the lips are appressed) and then cell
penetration (Doncaster and Seymour, 1973). Once inside the root and a
cell to be fed on was encountered, a different sequence occurred. Feeding
byAphelenchus avenae (Fisher, 1975) in liquid culture showed that
membrane penetration is not necessary for feeding, but several activities
are: cessation of body movement, followed by bending of the head,
stylet thrusting and protracted stylet exsertion during pumping of the
oesophageal metacorpus.
A given species typically exhibits the same migration and feeding
pattern in a wide range of plant hosts, and a small set of stimuli and
responses probably guide these activities. It has been suggested that CO 2
mediates the acropetal migration ofMeloidogyne spp. intercellularly
through the root cortex following root entry in cotton (McClure and
Robertson, 1973). After reaching the meristematic tissue just behind the
growing tip, these nematodes turn basipetally to rest and feed on one or
several cells, which are induced to develop into enlarged hypermetabolic
nurse cells, usually called giant cells. The same migration pattern is seen
in many hosts (Wysset al., 1992; VonMende, 1997). As one of many
possible contrasting examples, root entry by the infective, vermiform
females of the reniform nematode (R. reniformis) is largely intracellular,
rather than intercellular through the cortex, and perpendicular, rather
than parallel to the root axis. In a wide range of hosts, the infective female
usually comes to rest and feeds permanently on an endodermal cell,
eliciting the formation of a nurse syncytium comprised of several contig-
uous pericycle cells, without the nematode ever perforating the pericycle.
This same feeding-site establishment behaviour, like that of root-
knot nematodes, is exhibited in dozens of distantly related plant hosts
(Robinsonet al., 1997).Crop-protection opportunities
Only a few studies have explored interference with plant-parasitic
nematode behaviour as a crop-protection tool. These studies have exam-
ined co-formulation of the sex attractant, vanillic acid, with biological
control agents in pots and in the field (Meyer and Huettel, 1996; Meyer
et al., 1997) to manage the soybean cyst nematodeHeterodera glycines,
release of CO 2 as a bait (Bernklau and Bjostad 1998a,b) to increase the
efficacy of pelletized mycophagous fungi (Robinson and Jaffee, 1996),
manipulation of CO 2 and temperature gradients to increase Baermann
funnel extraction efficiency (Robinson and Heald, 1989, 1991), applica-
tion of lectins to block chemosensory function (Marbán-Mendozaet al.,
1987), shielding of plant roots with ammonium nitrate and other repellent
fertilizer salts (Castro et al., 1991) and application of tannic acid
attractants to the soil as confusants (Hewlettet al., 1997).Host Finding by Plant-parasitic Nematodes 101