A Y-tube olfactometer was used to test the olfactory responses of adult female predatory mites (P. persimilis) to plant volatiles [22]. The mites were individually introduced at the start point on a steel wire in a laboratory room at 25uC. The behavior of the mite on the wire was observed until the mite reached the far end (finish line) of one of the arms. The connections of the odor-source containers to the olfactometer arms were exchanged every five bioassays. Assays using 20 or 10 predators were carried out as a single replicate in a day. Three or four replications (i.e. 70–80 predators in all) were carried out on different days. The results from 3 or 4 replications of each experiment were subjected to a binomial test to evaluate whether the result in each experiment differed from the null hypothesis in which predators showed a 50:50 distribution between the two odor sources. Predators that did not pass the finish line of either arm within 5 min (‘‘no choice’’ subjects) were excluded from the statistical analysis.