REARING OF TRICHOSIROCALUS HORRIDUS (COLEOPTERA: CURCULIONIDAE) LARVAE IN ARTIFICIAL DIETS

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Abstract
Diet components of an initially acceptable diet for larvae of Trichosirocalus horridus (Panzer), an introduced weevil for thistle control, Carduus thoermeri Weinmann and C. acanthoides L., were systematically varied to determine if the yield of adult weevils could be improved. A total of 56 new diets were prepared and tested. Survival to the late third instar was slightly improved up to 39%, while larval development improved with additions of Vandersant Vitamin Supplement (8 g per 425 ml batch of diet), lyophilized thistle roots, ergosterol, or by transferring larvae to identical fresh diets after 4 weeks. However, larval survival decreased when excessive casein hydrolysate or 7-dehydrocholesterol was used. Sucrose did not improve larval growth. Of the six new diets that supported complete larval development, one diet yielded two adults, while the other five yielded one adult each. Only one of the diet-reared females oviposited eggs, and longevity of diet-reared adults was shorter than adults reared from its natural host, musk thistle.