compound that is apparently unique toSolanumspp. (Robinsonet al.,
1979). The latter case has been studied in some detail. The type host,
Solanum elaeagnifolium, accumulates attractant in all foliar tissues
throughout development, and the attractant can be collected by rinsing
foliage with water (Robinson, 1992). The infective fourth-stage juveniles
in soil can utilize gradients of the compound around the bases of stems
during rainy weather to locate stems, which they then ascend, invading
foliar buds up to 60 cm above the soil surface. Attractant activity is
retained during freeze-drying and is freely soluble in water (Robinson and
Saldaña, 1989), and so seems well suited for this purpose.Movement through plant tissues
The tissue migrations, feeding sites and reproduction of animal and plant
parasites have been studied in some cases for more than 100 years. The
last two decades have seen increased interest in the evolution of parasitic
behaviours, particularly in relation to host finding, site finding and
feeding-site establishment. A recent conceptual advance has been to
explain differential migrations in terms of a small number of fixed action
patterns elicited by different stimuli in different nematode species or at
different times during development (Sukhdeo, 1997). Examples include
the characteristic sequences of activities exhibited by plant-parasitic nem-
atodes during hatching and root invasion, the resumption of spontaneous
activity byS. carpocapsaeandAncylostoma caninumwhen vibrated or
byTrichonemasp. and Agamermis catedecaudatawhen illuminated,
nictating byS. carpocapsaeandA. caninumin response to CO 2 , con-
version from tortuous to straight locomotion by males ofPanagrellus
redivivuson agar when exposed to sex attractant (Samoiloffet al., 1973)
and accelerated movement by animal parasites in response to bile
(Sukhdeo, 1997).
VonMende (1997) reviewed movement of juvenile stages of sedentary
root parasites through roots, emphasizing work with the model plant,
Arabidopsis thaliana. Wyss (1997) examined literature for feeding-site
establishment in roots across a continuum of parasitic specialization
among 14 illustrated types of feeding patterns or nematode-induced feed-
ing sites. Schereset al. (1997) have discussed nematode-elicited cellular
and tissue modifications in plants in relation to contemporary genetic
analysis of cell determination in roots.
Based on interpretations of tissue migrations by animal parasites, it
seems plausible that a small group of fixed action patterns evoked in
plant-parasitic nematodes at key points during plant tissue development
and invasion may guide nematodes through tissue and regulate their
involvement in feeding-site establishment. In 11 species of Tylenchida,
contact with roots led to a predictable sequence of actions referred to as
local exploration (lip rubbing and stylet probing), followed by a cell-wall100 A.F. Robinson