Biological studies of iceplant scales, Pulvinariella Mesembryanthemi and Pulvinaria delottoi (Homoptera: Coccidae), in California
AuthorsJan O. Washburn
Gordon W. Frankie
Authors AffiliationsJan O. Washburn was a Postdoctoral Research Associate, Department of Entomology, University of California, Berkeley; Gordon W. Frankie was Professor of Entomology, Department of Entomology, University of California, Berkeley.
Hilgardia 53(2):1-27. DOI:10.3733/hilg.v53n02p027. June 1985.
Two scale species native to southern Africa, Pulvinariella mesembryanthemi and Pulvinaria delottoi (Homoptera: Coccidae), were discovered in California in the vicinity of San Francisco Bay between 1971 and 1973. Laboratory host-range tests indicate that both species are polyphagous on species of Aizoaceae, but in California these scales feed primarily on cultivated and naturalized ornamentals in the genus Carpobrotus. Some succulents in the Crassulaceae are also suitable hosts.
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, but it is likely to spread into all areas where P. mesembryanthemi occurs. The rapid spread of these scales has probably resulted from wind dispersal of the first instars.
Pulvinariella mesembryanthemi and P. delottoi are similar morphologically, but they differ in developmental time, selection of feeding sites by crawlers, and sex ratios. The developmental time of P. mesembryanthemi is approximately half that of P. delottoi, and under field conditions north of Monterey County P. mesembryanthemi is bivoltine while P. delottoi is univoltine. In Los Angeles and Orange counties, P. mesembryanthemi has three generations per year, but when reared in warm greenhouse conditions this scale can complete a generation in 11 weeks. First instars of P. mesembryanthemi preferentially settle on young iceplant leaves; P. delottoi tends to settle on more mature leaves. This differential settling results in partial spatial segregation on host plants. Both species reproduce parthenogenetically, though males of P. mesembryanthemi are commonly produced in low numbers. In both laboratory and field populations, sex ratios were always female biased, and matings were never observed. Although males of P. delottoi were produced very infrequently under laboratory conditions, they were never encountered in field populations.
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