Nickel hyperaccumulator plants contain at least 1,000 µg Ni/g dry mass. Their high-Ni tissues present a chemically unique resource for herbivorous insects. A prior survey of insects associated with the Ni hyperaccumulator Streptanthus polygaloides in California yielded a new species, Melanotrichus boydi Schwartz and Wall (Hemiptera: Miridae). Here we document the host preference of M. boydi. Surveys of 10 S. polygaloides populations across its geographical and elevational ranges documented the presence of M. boydi upon S. polygaloides at all sites. A host-choice experiment contrasting M. boydi with the polyphagous mirid Lygus hesperus (both collected from S. polygaloides) showed M. boydi preferred S. polygaloides but L. hesperus did not. Other host-choice studies showed M. boydi preferred S. polygaloides to 2 other ultramafic soil plant species in the Brassicaceae, including another species of Streptanthus. No preference was observed when M. boydi was offered samples from several populations of S. polygaloides or given a choice between high-Ni and low-Ni S. polygaloides plants. These results show that M. boydi feeds primarily on S. polygaloides but lacks population-level specificity. This is the first report of a North American insect species monophagous on a Ni hyperaccumulator species.