Phytophagous Insect Faunas of Dicoria canescens and Iva axillaris, Native Relatives of Ragweeds, Ambrosia spp., in Southern California, with Analyses of Insect Associates of Ambrosiinae

Abstract

This study completes a series of faunistic surveys of all genera and most species that compose the Subtribe Ambrosiinae of the Tribe Heliantheae (Asteraceae) in southern California. Phytophagous insects representing 7 orders, 30 families, 68 genera, and 77 species compose the insect fauna of Dicoria canescens Torrey & Gray in southern California. Similarly, phytophagous insects representing 7 orders, 25 families, 39 genera, and 47 species compose the insect fauna of Iva axillaris Pursh. Most insects on these native herbs are ectophagous, sap- and foliage-feeding insects. More than half, 38 (51%) of 74 of the identified species on D. canescens occur on other Ambrosiinae ( Ambrosia, Hymenoclea , and Xanthium spp.), as do 17 (46%) of 36 identified species on I. axillaris . Sixteen (21%) of the 74 species on D. canescens only feed on Heliantheae, including eight oligophagous species restricted to the Ambrosiinae and four monophages. On I. axillaris , 9 (25%) of the 36 species were restricted to the Heliantheae, including one oligophagous and three monophagous species. In total, 412 species of insects are now known to be associated with Ambrosiinae in southern California, 293 (71%) of which have been identified to species. Trophic, taxonomic, niche, and distributional characteristics of these phytophagous insects on Ambrosiinae are analyzed and compared with faunas of other species groupings and subtribes of native Asteraceae in North America and Europe. These findings also are reviewed and discussed relative to the biological control of ragweeds in North America and abroad.