The role of herbivore-induced volatile substances in prey-finding by phytoseiid mites has been
repeatedly documented using an olfactometer. The objective of the present paper is to test the
hypothesis that movement by Phytoseiulus persimilis is affected by these volatiles even on plants. Two
series of laboratory experiments were carried out. In the first series we studied searching behavior of P.
persimilis females on young bean plants in which a single leaf was infested with spider mites. The effect
of spider mite colony location on the walking pattern of predatory mites while on a leaf was studied in
the second series of experiments. We found that P. persimilis individuals were unable to discriminate
between infested and uninfested leaves when they walked up the stem of a bean plant. On the other
hand, results of the second series of experiments indicate that walk was not random once a predator
was on the leaf surface since it was attracted to the spider mite patch, at least over a distance of 1 cm.
These results thus demonstrate that herbivore-induced volatiles can be utilized by P. persimilis during
search for prey also under conditions that mimic natural situations better than an olfactometer does.