Washburn, J.O. 1984 . The Biology and Ecology of Iceplant Scales, Pulvinariella mesembryanthemi and Pulvinaria delottoi, in California. University of California, Berkeley, Ph.D. Thesis 148 pp.

Notes: [Ph.D. Thesis.] Pulvinariella mesembryanthemi and Pulvinaria delottoi (Homoptera: Coccidae), were discovered in several California counties in the vicinity of San Francisco Bay between 1971 and 1973. In California these scales from southern Africa feed predominately on cultivated and naturalized ornamentals in the Aizoaceae, principally those in the genus Carpobrotus. Pulvinariella mesembryanthemi has spread rapidly throughout the coastal regions of the state, and its current geographical range extends from San Diego County in the south to Napa County in the north. The scale is also reported from Yolo and Sacramento counties in the Central Valley. Pulvinaria delottoi is presently restricted to counties surrounding San Francisco and Monterey Bays. The rapid spread of these scales has resulted primarily from active wind dispersal of the first instars or crawlers. Crawlers exhibit an age specific behavior response to air streams. This behavior involves standing on the meso- and metathoracic legs while exposing the maximum body surface area to the wind stream. This posture increases the frictional drag experienced by the insect and enhances the likelihood of becoming airborne. Pulvinariella mesembryanthemi and P. delottoi are similar morphologically, but they differ in developmental time, leaf selection of settling crawlers, and sex ratios. The developmental time of P. mesembryanthemi is approximately half that of P. delottoi: under field conditions north of Monterey County P. mesembryanthemi is bivoltine while P. delottoi is univoltine. At field sites in Los Angeles and Orange Counties, P. mesembryanthemi has three generations per year, but when reared in warm greenhouse conditions this species can complete a generation in 11 weeks. First instars of P. mesembryanthemi preferentially settle on young iceplant leaves while P. delottoi tends to settle on more mature leaves. This differential settling results in partial spatial segregation on hosts. Both species reproduce parthenogenetically, though males of P. mesembryanthemi are commonly produced. In both laboratory and field populations, sex ratios were always female biased, and matings were never observed. Males of P. delottoi are virtually unknown, and they were never encountered in field populations.