Assessing the biodiversity and the impact of pollinators on carob production

Farmers are highly dependent on pollinators, reinforcing the fact that pollinator conserva- tion is an anthropogenic pursuit [56, 57]. Beehive renting is common to enhance the pollina- tion of apple trees and other crops [58]. The results of the present study suggest that management to enhance bee populations within or around carob fields could significantly increase pod yield. Wild bees represent an alternative solution, as they inhabit agricultural landscapes and can use pollen and nectar from cultivated crops for their nutrition, simulta- neously pollinating the flowers they visit [58]. At the same time, carob trees are important for wild bees. While the current work did not quantify the importance of carob flowers for wild bee nutrition, carob flowers are a very abundant resource during autumn, a period of generally low flower availability in the Mediterranean. Ameliorated understanding of how pollination services can be manipulated could lead to additional practical management guidelines for building sustainability into agricultural systems to protect both, pollinators and crops. Conclusions Ceratonia siliqua shows great tolerance to arid and semi-arid climates, an increasingly impor- tant trait for environmental, economic, and social reasons because of the changing climate. The current work highlighted the importance of insect pollination and especially of pollinators belonging to the order Hymenoptera, in maintaining high production of carobs, as well as improving pod quality. Taking into consideration the pollination biology of carob trees, fur-

ther research needs to focus on the identification as well as the assessment of the contribution of night visitors to carob pollination. An additional potential area of future research is the eval- uation of the effectiveness of different pollinator species in providing pollination services. Fur- ther work on pollen dispersal by wind will improve our understanding of the contribution of wind to carob pollination and can lead to practical recommendations for the density of female vs male trees to maximize production, especially in areas with low pollinator abundance. Acknowledgments We thank Achik Dorchin (IL) for his advice and suggestions at the beginning of this research and Ioannis Vogiatzakis (CY) for his help on the landscape characterization of our experimen- tal regions; Holger Dathe (DE) (Hylaeus), Michael Kuhlmann (DE) (Colletes), Thomas Wood (UK) (Andrena) for the identification of the specimens. We should also thank the Holy Trans- figuration Monastery and the nuns in Avdellero (Larnaca region) who allowed us to carry out the experiments in their carob tree fields and especially the nun dagger;Sigklitiki with whom we had frequent contact. In addition, the owners of all sampling plots in every experimental region and John Varnava and Kyriaki Varnava for their advice and help during the experiments. Author Contributions Conceptualization: Androulla I. Varnava, Menelaos C. Stavrinides. Formal analysis: Androulla I. Varnava, Menelaos C. Stavrinides. Investigation: Androulla I. Varnava. Methodology: Androulla I. Varnava, George A. Manganaris, Menelaos C. Stavrinides.

Supervision: Menelaos C. Stavrinides. Visualization: Menelaos C. Stavrinides. Writing – original draft: Androulla I. Varnava. PLOS ONE Biodiversity and the impact of pollinators on carobs PLOS ONE | https://doi.org/10.1371/journal.pone.0291431 October 20, 2023 13 / 16