Incidence of Dicymolomia julianalis (Lepidoptera: Pyralidae) on Musk Thistle in Tennessee

The incidence of the pyralid Dicymolomia julianalis (Walker) on musk thistle, Carduus thoermeri (Weinmann), was monitored at 15 sites in eastern and middle Tennessee during 1989 and 1990. Seed heads infested by larvae and/or pupae of D. julianalis were recovered from all sites. During 1990, infestation levels of mature seed heads at each site on each sampling date ranged from 0 to 30.9%. Of 2,570 seed heads collected from all sites during 1990, 14.2% (365) was infested by D. julianalis. Larvae of D. julianalis were observed to feed on seeds of musk thistle, and a mature seed head that had been infested by as few as one larva did not release seeds. However, the interactive association of D. julianalis and musk thistle is unclear because of its reported diversity of food types and habitats. Our results suggest that seed production and proliferation of musk thistle were apparently reduced by D. julianalis.