Host utilization patterns of species of Hemisarcoptes (Acari: Astigmata: Hemisarcoptidae), which parasitize armored scale insects (Homoptera: Diaspididae), are reviewed. The mites optimally parasitize ovipositing scale females, on which they exhibit an aggregated distribution and produce the most progeny. However, Hemisarcoptes spp. cannot attack this stage of the California red scale [Aonidiella aurantii (Maskell)] because the host body is appressed to its shield; the parasite therefore subsists on younger scale stages. Due to the slower development of univoltine scales in colder climates, ovipositing females are available to the mites only briefly, and so suboptimal host immature stages are mostly attacked. Host plants of the scales affect mite life history by having rough or smooth surfaces, which engender, respectively, easy or difficult access beneath diaspidid shield covers. During their deutonymphal (hypopodial) stage, species of Hemisarcoptes are disseminated by coccinellid beetles of the genus Chilocorus. These deutonymphs appear to obtain some molt-inducing chemicals from the beetles, which may therefore be regarded as true hosts. Deutonymphs prefer to settle on glabrous areas on the underside of beetle elytra; these areas differ in size among species of Chilocorus and thus influence their mite-carrying capacity. The diet of beetle larvae affected the sex ratio of mites which had sojourned on them. These different patterns of host (scale and/or plant and/or beetle) utilization may affect the efficacy of Hemisarcoptes spp. as biological control agents.