We explored competing mechanistic hypotheses by which northern spicebush (Lindera benzoin : Lauraceae) experiences a pattern of reduced herbivory when found in association with black walnut (Juglans nigra : Juglandaceae). Using Epimecis hortaria (Geometridae), a primary spicebush herbivore, we conducted experiments to determine whether this associational resistance was achieved by 1) throughfall of walnut allelochemicals onto spicebush leaves, 2) reduced viability of pupating Epimecis via altered soil environments, 3) incorporation of walnut allelochemicals into spicebush tissues, or some combination of these mechanisms. Expanding on preliminary results demonstrating reduced growth rates of late instar Epimecis larvae reared on spicebush leaves collected under walnut canopies, we examine this relationship throughout larval development. Following up on studies demonstrating reduced emergence success of surrogate lepidopteran herbivores (Spodoptera exigua and Agrotis ipsilon) in soil collected from under walnut canopies, we examined the response of Epimecis and experimentally manipulated biotic components of sample soils – including previously identified entomopathogenic fungi. Spicebush tissues were assayed for walnut allelochemicals using HPLC. The relative importance of these factors in affecting variable spicebush herbivory is discussed.
