Trupanea bisetosa (Coquillett) is reported from capitula of wild and cultivated sunflowers, Helianthus annuus L., and blueweed, H. ciliaris Decandolle. The immature stages of this multivoltine tephritid are described and illustrated. One to several eggs are laid among the developing disk florets of young capitula. The eggs hatched in ca. 4 days. Each larva damaged five to eight disk florets (including the immature achenes) during its three stadia. Pupariation occurred inside the feeding cavity. Adults lived 2 to 3 months in insectary cagings. Eleven females each laid a total of 90 plus or minus 12.7 (x@u- plus or minus SE) eggs. Territorial behavior was shown by ovipositing females. Courtship involved wing displays alternating with walking forward in spurts by males. Mating occurred in the early morning and lasted ca 6 min. Postmating behavior included grooming by both sexes. Reproduction; Reproductive behaviour; Courtship; Reproductive productivity; Life cycle and development; Development; Behaviour; Comfort behaviour; Parasites diseases and disorders; Parasites; Insect parasites; Hosts; Insect hosts; Land and freshwater zones; Nearctic region; North America; USA Trupanea bisetosa (Tephritidae); Courtship display; Mating; Oviposition; Site on Helianthus annuus (sunflower); Fecundity; Life cycle and development; On Helianthus annuus (sunflower); Longevity; Territoriality; Ovipositing females; Grooming; Postmating behaviour; Hymenopteran parasites; Pteromalus & Bracon nuperus; Plant hosts; Helianthus annuus (sunflower); Southern California; California; South; Life cycle on Helianthus annuus (sunflower) Bracon nuperus (Braconidae ); Pteromelus (Habrocytus) (Pteromalidae ); Dipteran hosts; Trupanea bisetosa; Southern California; California; South; Dipteran host