D3288: Investigations of the Yucca moth (Tegeticula antithetica) interactions with the eastern Joshua tree (Yucca jaegeriana)

Joshua trees are long-lived monocot trees endemic and iconic to the Mojave Desert of the U.S. Southwest. The tree occurs in two taxonomic forms and for each reproduction depends on a mutualistic interaction with specialist moth pollinators of the genus Tegeticula. Changing environmental conditions pose threats to one or both partners in this interaction; yet the environmental conditions necessary for successful Joshua tree-moth interaction are unknown. This leads to the overarching question of maintenance of the phenological synchrony between the Joshua tree and its specialized pollinator with climate change. In the spring of 2022, we initiated a study of the eastern Joshua tree (variously Yucca brevifolia var. jaegeriana or Y. jaegeriana) and its specialized pollinator, T. antithetica, to characterize the environmental parameters supporting the mutualism. Joshua trees were identified at sites along an elevational gradient in the Arizona Joshua Tree Forest of NW Arizona. We designed a method of trapping which allowed us to document the occurrence of T. antithetica. For each tree, we measured climatic variables, recorded aspects of tree density and reproductive ecology, trapped insects as they approached open Joshua tree flowers, and evaluated seed production. In this presentation, our first-year findings of the relationship of moth activity, environmental parameters, and seed production are presented. We also discuss future steps to elucidate the timing of flowering of the Joshua tree and its relationship to emergence from the soil of the diapausing moth pupae.