Biological studies of iceplant scales, Pulvinariella Mesembryanthemi and Pulvinaria delottoi (Homoptera: Coccidae), in California

Abstract

Iceplants (Carpobrotus spp.) are extensively cultivated in California as an ornamental ground cover along roadside banks and on sites with a high risk of soil erosion, but in some coastal areas where they have displaced the indigenous vegetation they are considered as invasive weeds for which biological control by insects is required. Pulvinariella mesembryanthemi [Pulvinaria mesembryanthemi] and P. delottoi, which were accidentally introduced from South Africa into California and spread rapidly along the coast, are therefore of economic importance both as pests and as potential biological control agents of these plants. The species are morphologically similar, but P. mesembryanthemi was found to develop at least twice as fast as P. delottoi; out of doors it had 2-3 generations a year (while P. delottoi was univoltine), and in a warm greenhouse it completed a generation within 11 days. Newly hatched nymphs of P. delottoi preferred older leaves of Carpobrotus than did those of P. mesembryanthemi, which resulted in partial spatial segregation of the 2 species on the plants. Both species reproduced parthenogenetically; small numbers of males of P. mesembryanthemi were produced in the field but mating was never observed, and males of P. delottoi were observed occasionally in laboratory cultures but never in the field.