Phytophagous Insect Faunas of Native Cirsium Thistles, C. mohavense, C. neomexicanum, and C. nidulum, in the Mojave Desert of Southern California

Abstract

Phytophagous insects representing seven orders, 19 families, 25 genera, and 30 species compose the insect fauna on Cirsium mohavense (Green) Petrak (Asteraceae) in southern California. Similarly, phytophagous insects representing six orders, 17 families, 18 genera, and 23 species from Cirsium neomexicanum Gray, and insects representing six orders, 11 families, 12 genera, and 12 species from Cirsium nidulum (Jones) Petrak, are reported. Most insects feeding on these thistles are polyphagous, ectophagous, sap- and foliage-feeding species. Few or no insect species or individuals were reared from within the flower heads, stems, crowns, and roots of these desert thistles. Like other native Cirsium thistles surveyed in southern California and discussed here, the food niches represented by this natural assemblage of host plants are not saturated with phytophagous insect species. Significance of these underused resources and apparently “empty” food niches for biological control of weedy thistles in North America is discussed. Some members of the insect faunas on Cirsium thistles have markedly broader feeding niches than their counterparts in Europe, compensating for this host-plant underuse. Taxonomic compositions and niche characteristics of phytophagous insect faunas on native thistles in Europe and southern California are compared and discussed in evolutionary terms.