Phytophagous insects representing 5 orders, 32 families, and 89+ species are reported as comprising the insect fauna ofAmbrosia dumosa(Gray) Payne (Compositae) in southern California. Most insects found attacking this native ragweed were euryphagous, ectophagous, sap- and foliage-feeding species. About ½ reproduced on this plant. Twenty-one (46%) of the 46 associates identified to species were stenophagous, their hosts apparently confined to the tribe Heliantheae. Only 5 (11%) of these were minor or major pests of cultivars.