The present paper concerns mainly with effect of the density of Unaspis yanonensis (Kuwana) on searching by Aspidiotiphagus citrinus (Craw). By liberating a single female parasite against either female or male larvae of host at the first instar settled on a citrus leaf at different densities, the author examined the time spent by the parasite on the leaf and the number of hosts found and parasitized. Each experiment was repeated five times at the temperature of 25℃. Most of female hosts settled on the central vein of the leaf whereas male hosts settled a colony in the interveinal area. Parasites used in this experiment were two days old. The time spent by the parasite on a leaf and the number of hosts found and parasitized were dependent upon host densities. These responses to host densities were slightly sigmoid in form. But there were differences in response curves between female and male host. An analysis indicated that the number of female hosts found per unit time increased with increase of the host density, while the number of male hosts found per unit time was almost same through host densities. The number of hosts found by the parasite was higher in male hosts than in female hosts. But the number of hosts parasitized by the parasite was lower in male hosts than in female hosts because oviposition by the parasite in male hosts was sometimes disturbed by their excretion of threads. Thus the percent parasitism of the female host increased as the host density increased, and it was higher than that of male hosts.