FIELD STUDIES ON THE REPRODUCTIVE CAPACITY AND DEVELOPMENT OF CASSIDA-RUBIGINOSA (COLEOPTERA, CHRYSOMELIDAE) ON MUSK AND CANADA THISTLES

The reproductive capacity and development of Cassida rubiginosa Muller , a defoliator of Canada thistle, were examined on Canada thistle and musk thistle under field conditions. Field-collected, overwintered fem ales produced 61.1 +/- 29.9 oothecae per individual during a 15-wk per iod. They showed no preference for oviposition between musk and Canada thistle. Development from egg to adult in field cages required 27.4 /- 1.7 d when reared on Canada thistle and 28.5 +/- 2.1 d on musk this tle. Mortality of the immature stages caused by incomplete development totaled 52.5% when reared on Canada thistle and 79.0% on musk thistle . Survival from egg to adult beetles was 18.3% in the 1st yr and 26.7% in the 2nd yr.