First Record of a Gall-Inducing Mordellid in North America: Pseudomordellina hattorii (Coleoptera: Mordellidae) Induces Galls on Common Mugwort, Artemisia vulgaris in the Northeastern United States

Previously undescribed stem galls have been observed on the introduced Eurasian plant Artemisia vulgaris L. in several states in the Eastern United States. Community naturalists have reported that unidentified mordellid beetles are associated with these stem galls, but it has been unclear if the beetles are gall inducers, gall inquilines, or stem borers. Herein we identify the mordellid from A. vulgaris galls in Pennsylvania as Pseudomordellina hattorii (Tokeji), a species previously known only from Japan where it is associated with stem galls on A. indica var. maximowiczii. We also provide definitive evidence that the mordellid beetles we have reared from overwintering mugwort galls from Southeastern Pennsylvania, as well as field-caught mordellids associated with mugwort plants, have the capacity to induce stem gall formation on A. vulgaris. Pseudomordellina hattorii is the first known gall-inducing mordellid in North America, and the gall that P. hattorii forms on A. vulgaris, is the first known type of insect gall on this frequently invasive plant in North America.