Phytophagous Insect Faunas of Two Introduced Cirsium Thistles, C. ochrocentrum and C. vulgare, in Southern California

Abstract

Phytophagous insects in seven orders, 18 families, 27 genera, and 30 species are reported as composing the insect fauna of bull thistle, Cirsium vulgare (Savi) Tenore, a weed introduced from Europe into southern California. Similarly, phytophagous insects representing four orders, six families, six genera, and seven species are reported from a single population of yellow-spine thistle, C. ochrocentrum A. Gray, also an introduced thistle, but native to states east of California. Most insects attacking bull thistle are polyphagous, ectophagous, sap- and foliage-feeding species. Seventeen (61%) of the 28 identified insect species reported from bull thistle also occur on native Cirsium thistles in southern California. Six (35%) of the 17 insect species feeding on bull thistle as well as native species of Cirsium are stenophagous (i.e., apparently restricted to host plants in the subtribe Carduinae). All six identified species reported from yellow-spine thistle also occur on native Cirsium thistles in southern California, including three endophages and two oligophages (i.e., apparently restricted to the genus Cirsium ). Faunal characteristics suggest that yellow-spine thistle is related more closely to Cirsium thistles native to southern California than to bull thistle.