Abstract/Summary

Wild bees (Hymenoptera: Anthophila) are important pollinators and essential for maintaining ecosystem health. The majority of bee species are ground-nesting, and all bees spend most of their lifetime inside the nest. Still, most studies and monitoring schemes assess wild bees during flower visitation, allowing no conclusion about their nest sites. Methods for locating and assessing the ground nests of bees are currently limited, hindering scientific progress and conservation efforts. To evaluate and improve methods for locating and assessing ground nests, we combined information from a literature review and our own empirical studies. Methods ranging from established field methods (visual nest observations and emergence traps) to new technological approaches (marking and tracking individuals) are compared in terms of success in catching nesting bees and identifying nest locations, time effort required to implement the methods, and limitations. We provide guidelines and recommendations on the use of the different methods depending on the data requirements and study locations. We also present a novel emergence trap design and two newly developed marking methods, using a radioactive tracer substance and a retroreflective pigment, and show that these methods can be used to successfully locate and assess ground-nesting habitats of bees. With this work, we address gaps in current research methods and aim to enhance the efficiency of field research that explicitly targets ground-nesting bees and their nest sites in various environments. By providing a comprehensive overview for researchers and practitioners, we demonstrate how to improve knowledge about the ecology and life history of ground-nesting bees and thus support efforts for their conservation.