Dioxyna picciola (Bigot) is bivoltine or trivoltine and oligophagous primarily on Coreopsis and Bidens spp. in southern California. It is a late-stage, aggregated attacker in flower heads at or past anthesis. Mating and oviposition by overwintered F-2 and F-3 adults occurs in spring on wild and cultivated Coreopsis spp. Eggs are inserted into soft achenes in which the first two instars and most early-third instars feed solitarily; the late-third instars also feed on sap, and at higher larval densities, score the receptacles and feed on sap accumulated in shallow depressions. Pupariation occurs in heads, with puparia resting in the feeding depressions, or in flower heads containing only a single larva, within hollowed out achenes and situated well above the receptacle. Adults are synovigenic, sexually immature at eclosion, but exceptionally long-lived as the overwintering stage. This tephritid is known in North America as D. picciola, but it recently was synonymized with the cosmopolitan D. sororcula, but unlike the latter species, Nearctic flies have not been reported from Calendula officinalis L. The egg is described and illustrated and differs from the eggs of two other species in the closely related genus Campiglossa (=Paroxyna) by the elongate, apically expanded pedicel, which bears aeropyles apically. First through third instars and the puparium also are described and illustrated. Third instars of D. picciola are similar in morphology to those of Campiglossa genalis (Thomson), but are more elongate and cylindrical, have a gnathocephalon that is broader apically, with serrated rugose pads dorsomediad of the anterior sensory lobes. The anterior sensory lobes are larger and more prominent and the serrated rugose pads laterad of the mouth lumen are larger and more numerous than in two Campiglossa spp. that have been described in similar detail. Behaviors of adults of D. picciola and C. genalis in southern California were similar, but differed in several respects from D. picciola on C. officinalis in India. Wing lofting by D. picciola and such unique aspects of its mating behavior in southern California as its copulatory induction behavior and mate guarding are described.
