Seasonal Asynchrony of Italian Thistle, Carduus pycnocephalus , and the Weevil, Rhinocyllus conicus (Coleoptera: Curculionidae), Introduced for Biological Control in Southern California

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Abstract
Thirty Italian thistle ( Carduus pycnocephalus L.) plants produced a total of 7,735 (mean, 258) flower heads, which potentially contained ca. 25,000 seeds, from mid-April to late August 1980, at See Canyon, San Luis Obispo County, Calif. Rhinocyllus conicus Froelich larvae directly and indirectly caused an estimated 55% seed loss in these heads, but still allowed production of 11,410 seeds, mainly after oviposition by the univoltine weevils ended in late June. Larval mortality of 45%, mostly in early instars, was due to intraspecific competition in flower heads. This competition was of the scramble type. Negligible interspecific competition in heads resulted from lepidopterous larvae.