LIFE-HISTORY AND DESCRIPTION OF IMMATURE STAGES OF XENOCHAETA-DICHROMATA SNOW (DIPTERA, TEPHRITIDAE) ON HIERACIUM-ALBIFLORUM HOOKER IN CENTRAL AND SOUTHERN CALIFORNIA

Xenochaeta dichromata Snow is a nearly monophagous, uni-or bivoltine, synovigenic, seed-feeding fruit fly attacking the flower heads of cert ain native hawkweeds (Hieracium spp., Asteraceae) in western North Ame rica. Xenochaeta aurantiaca (Doane) is synonymized with X. dichromata. The egg, first-third instar larvae, and puparium are described and al l but the second instar are illustrated. The third instar is shagreene d, i.e., meso-, metathorax, and abdominal segments are covered by minu te, dome-shaped verrucae. Xenochaeta dichromata differs from other sha greened species in possessing a single row of verruciform sensilla cir cumscribing each thoracic and abdominal segment. The life cycle is of the aggregative type. Eggs are deposited singly in individual immature flower heads. Each larva consumes the entire contents of a single hea d, within which it overwinters as a prepuparium. Pupariation occurs in the spring and the newly emerged adults aggregate on the preblossom h ost plants to mate and oviposit. The possible use of this fly for biol ogical control of hawkweeds in North America and abroad, e.g., in New Zealand, is discussed.