Scotch broom (Sarothamnus scoparius (L.) Wimmer) and its insect fauna introduced into the Pacific northwest of America.
Abstract
The following is based largely on the author's sumrnary. Scotch broom (Sara-thamnus scoparius) was introduced from Europe to the Pacific toast of North America, where it spread and has become a weed [c.f. RAE A 52 526]. The main siles where it grows in Calirornia and British Columbia were visited between mid-June and the end of July 1963, and the insect fauna of the plant was examined. Some of the introduced species found are new records for California or for Brítish Columbia. Most of the introduced insects were species that aestivate or hibernate in their immature stages under the bark of young items. They were probably trans ported with young plants that were introduced either deliberately or accidentally in ballast. The flies Micropeza lateralis Mg and Minettia fasciata (Fall) were most probably carried over as puaria in broom litter in bailase. The most abundam insects on broom in California were the Mirid Orthotylus concolor (Kirschb.), the Lyonetiid Leucoptera spanifolletla (Hb.) [cf. loc. cit.] and the Psyllid Arytaina sparti (Guér.) (spatiophla (Forst.)). The fauna on broom in British Columbia is much richer, and the most abundant insect was O. virescens (Dgl. & Scott). The populations of O. concolor in California and O, virescens in British Columbia were enormous. Their expansion is probably associated with favourable climatic conditions and with the absence of many natural enemies, notably the early hatching broom Mirids, which are predacious as well as phytophagous. Samples from populations of broom Mirids from North America were compared with those from southern England [cf. 56 2680]. Eight characters were measured and subjected to the canonical variate analysis. The ranges of variation in samples of populations of O. virescens from southern England were as great as those between different geographical regions. O. concolor is a more plastic species, but although its populations may have been isolated for more than 100 generations in the Sierran foothills in California, no major departures were found in the characters studied.