Biology of Cassida rubiginosa1 a Thistle-Feeding Shield Beetle2

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Abstract
Cassida rubiginosa Müller is distributed in northeastern North America from southern Canada, southward to northern Virginia and westward to Ohio and southern Michigan. The insect is univoltine in Virginia. The overwintering adults 1st appeared on Carduus nutans L. (musk thistle) during late winter and began to oviposit in early spring. The new generation of adults emerged in late spring and was found on thistles as late as Nov. 1. A laboratory population of C. rubiginosa collected in late winter produced an avg of 815 eggs/female and both sexes lived an avg of 38 wk. Females generally ate more than males. Development from egg to adult required an avg of 20 days at 32.5°C, 26 days at 26.6°C, 41 days at 21.1°C, and 60 days at 17.8°C. The threshold temperature for development from egg to adult was calculated to be 10.4°C. Adults are difficult to sex.

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