Biology of Two Weevils, Ceutorhynchus trimaculatus and Trichosirocalus horridus1 , on Carduus spp. 2 in Europe

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Abstract
Field studies were conducted at Rome, Italy, on Ceutorhynchus trimaculatus (F.) and Trichosirocalus horridus (Panzer), two candidate insects for the biological control of Carduus thistles in the United States. The biologies of these weevils were similar; teneral adults appeared in the spring and fed for 2 to 3 weeks on leaves of the primary host, Carduus macrocephalus Desfontaines, before estivation in the soil. Both weevils resumed feeding in the fall. Mating and oviposition occurred from November to March. Eggs of C. trimaculatus were laid on the surface and under the epidermis of the leaves, whereas eggs of T. horridus were laid in feeding grooves in the midrib. Larvae of both species fed together in the crowns and buds from December to April, but no cannibalism was observed. More larvae of T. horridus fed in buds than did larvae of C. trimaculatus . Pupation occurred in the soil. Both weevils were univoltine.

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