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.