Observations were conducted in southern Florida on Aulacaspis yasumatsui Takagi (Hemiptera: Sternorrhyncha: Diaspididae), a recently introduced armored scale insect native to Southeast Asia. The insect's host plants, exclusively cycads, were identified in the following genera: Cycas (Cycadaceae); Dioon, Encephalartos, Microcycas, (Zamiaceae), and Stangeria (Stangeriaceae). Cycas spp. seemed to be preferred over other cycad genera by this insect. Aulacaspis yasumatsui infested pinnae, rachides, strobili, stems, and roots of various species of cycads. It generally infested all above-ground plant parts of Cycas spp. and sometimes the primary and secondary roots to a soil depth of 60 cm. No morphological differences in the frond- and root-infesting forms were noted. At an ambient temperature of about 24.5C, eggs hatched in 8-12 days. In the field, some individuals developed to second instars in 16 days and third instars in 28 days. Third instars (mature females) laid >100 eggs. Most of the females of a generation did not live longer than 75 days. No natural enemies were observed. The scale insect populations became extremely dense and killed 100% of 15 Cycas revoluta Thunburg within a year of infestation. Between 1996 and June 1998 the insect spread from a limited area in southern Miami to various sites as far as 120 km north, probably by movement of plants.