Suitability of three armored scale insects (Homoptera: Diaspididae), their stages, the host plants and their parts, for the parasitic miteHemisarcoptes coccophagus Meyer was investigated. The studied scales were chaff scales,Parlatoria pergandii Comstock andP. cinerea Hadden, infesting grapefruit and orange orchards, latania scale,Hemiberlesia lataniae (Signoret), and oleander scale,Aspidiotus nerii Bouche occurring on acacia (Acacia cyanophylla) branches and leaves. Host suitability was evaluated by mite survival, mean intensity (active mites/attacked scales) and fecundity. It was highest on latania scale, lowest on oleander scale and intermediate on chaff scales. Results of laboratory experiments were consistent with these field findings: while developing on oleander scale, mites suffered 3× higher mortality, and their generation time was twice as long as on latania scale; the full egg clutch on the latter was high whereas on oleander scale it was negligible. Our data suggest that ovipositing females of latania and oleander scales, but not of chaff scales, are more suitable hosts than young scale females and the latter more suitable than immature stages. No direct effects of acacia plant parts on host suitability were detected. Citrus species affected chaff scale suitability for the mite through their effect on host diaspidid size. The ability ofH. coccophagus to control pestiferous diaspidids may depend on the specific host scale, its age structure and the specific host plant. The implications of these findings for the biological control of armored scale insects are discussed.