Euaresta stigmatica Coquillett is bivoltine and nearly monophagous on four native ragweeds, Ambrosia spp. (Asteraceae), in the southwestern United States. In southern California, larvae of the spring (F1) generation develop singly in and feed on one or both ovules of young fruiting involucres of Ambrosia ilicifolia (Gray) Payne, with a small proportion infesting the staminate involucres. Adults emerge after ≈1 mo, with their reproductive organs immature. The F2 generation develops in the involucres of fall-blooming Ambrosia acanthicarpa Hooker. The egg is described and illustrated for the first time for any species of Euaresta. First, second, and third instars and the puparium are described and illustrated for the first time for E. stigmatica. The posterior spiracular plates of all three instars bear only three interspiracular processes, whereas the larvae and puparia of all other nonfrugivorous tephritids described to date bear four such processes. Adult behaviors described from field and laboratory studies include courtship, copulation, and territoriality. Male courtship displays include three behaviors previously undescribed for Tephritidae: a side-to-side dance, rapid side stepping,and a middle leg abduction. Hymenopterous parasitoids of E. stigmatica include two solitary, primary larval-pupal, endoparasitoids, Eurytoma sp. (Eurytomidae) and Pteromalus sp. (Pteromalidae). Potential use of E. stigmatica as a biological control agent for ragweeds in Eurasiais discussed.


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