Solitary ground-nesting bees and their nesting preferences
Written by: Konstantinos Tsiolis
There are more than 20,000 known bee species worldwide which vary significantly in their size, habits and appearance having adapted according to the plants they like to visit. More than 85% of existing bee species are not social, like honeybees, but solitary. Solitary bee females mate independently, create their own nests containing about ten brood cells (depending on species), provide enough food for each offspring (pollen and nectar), lay an egg in each cell and finally die before the next generation emerges (see Fig. 1). Approximately 70% of solitary bee species nest in underground burrows (commonly called mining bees).
Figure 1: Generalised life stages of ground-nesting bees. 1 – Initiation, 2 – Construction, 3 – Development, 4 – Overwintering, 5 – Emergence (Harmon-Threatt 2020).
Solitary bees need both flowers for food and suitable habitat to nest in. Ways of providing food resources are well known, but the nesting preferences of such species are under researched and poorly understood. My research project aims to identify the key nesting parameters for ground-nesting bees as a basis to develop practical ways to enhance nesting resources in commercial orchards. Research at the University of Reading shows that the value solitary bees to UK apple pollination can be costed at around £51 million, and the main apple pollinators are the ground-nesting bees Andrena dorsata, Andrena nitida and Andrena haemorrhoa (Garratt et al. 2016). However, very little is known about where they nest in apple orchard landscapes and what their specific habitat nesting preferences are. One of my studies aims to provide novel insights into nesting preferences of such species and identify simple management interventions which can be used to enhance populations of these important pollinators. The findings of this project will underpin more general implications for the sustainable management of largely overlooked pollinating taxa which have a central role in food security.
One of the most challenging parts of this research is finding enough nests of species of interest. It is reasonably easy to spot ground-nesting bee nests at the beginning of nesting as there is a fresh “tumulus” around the entrance of each nest which is created during the excavation stage (Fig. 2). However, the “tumulus” could get washed away in the unfortunate case of having heavy rain and increase the difficulty of spotting them as they might look like holes excavated by ants or worms. Furthermore, I noticed that such species sometimes nest under vegetation which can increase the difficulty of spotting them even further (Fig. 3).
I am still in the process of collecting data, and I am looking forward sharing my findings with you all in the near future.
Figure 2: Andrena haemorrhoa exiting its nest early in the morning
Figure 3: Searching for bee nests at the edge of an apple orchard.
I would like to thank Waitrose CTP and Worldwide Fruit Ltd for funding for my research, and my supervisors Prof. Simon Potts (University of Reading), Dr. Michael Garratt (University of Reading) and Dr. Michelle Fountain (NIAB East Malling Research) for the continuous support and advice.
Harmon-threatt A (2020) Influence of Nesting Characteristics on Health of Wild Bee Communities. Annual Review of Entomology 65:39–56.
Garratt MPD, Breeze TD, Boreux V, Fountain MT, McKerchar M, Webber SM, Coston DJ, Jenner N, Dean R, Westbury DB, Biesmeijer JC, Potts SG (2016) Apple pollination: Demand depends on variety and supply depends on pollinator identity. PLoS ONE 11:1–15.