Assessing the biodiversity and the impact of pollinators on carob production

species, such as A. mellifera, are considered the leading pollination providers [10]. However, the threats faced by honey bees over recent years increased the importance of wild bees as alternative or complementary providers of pollination services [11, 12]. Wild bees contribute to the pollination of many crops, such as coffee, melon, tomato, sunflower, canola, blueberries, apple, and almonds, among many others [9, 13]. According to Maclnnis et al. [14] strawberries pollinated by wild bees were heavier than those pollinated by honeybees. The pollination effec- tiveness depended on wild bee abundance as floral pollen loads were not affected by species richness. In another study, wild bees were identified as the most important pollinators with strawberry fruit produced having fewer malformations, greater weight and longer shelf-life, resulting in higher commercial value [15]. Similar results have also been reported for other fresh fruits, such as sweet cherry [4]. In addition, a higher diversity and abundance of wild bees resulted in enhanced fruit set in apple orchards [12]. The use of managed solitary bees like Osmia can increase fruit set in almond orchards, where a small population ensured effec- tive pollination even though domesticated bees were 10 times more abundant [16, 17]. The carob tree (Ceratonia siliqua L) is an underutilized crop with descending trends regard- ing production volumes, yet it represents an excellent model of a heat- and drought- resistant crop, grown in dry areas with practically no inputs [18, 19]. It is an evergreen dioecious species

with some hermaphroditic forms and high longevity [20]. Carob tree domestication in the Mediterranean region dates back to the Roman times and was associated with the introduction of scion grafting in the Mediterranean basin [20, 21]. Work by Baumel et al. [21] points out to multiple origins of domestication of locally selected genotypes, as well as scattered long-dis- tance westward dispersals, along migration routes by Romans, Greeks and Arabs. In the last decades, cultivation spread in areas with a similar climate to the Mediterranean, including Cal- ifornia, Arizona, Mexico, Argentina, Australia, India, and South Africa [20]. Carob pods have traditionally been used as feed for livestock [22], and for human nutrition, consisting of dietary fiber, sugars, and a range of bioactive compounds, such as polyphenols and pinitol [20, 23, 24]. Carob cultivation is linked to the culture and traditions of Cyprus; in the past the crop has had substantial importance to the rural economy [18]. Currently, the remaining carob trees (ca. 2000 ha) are a defining feature of the high nature value farmland landscape of Cyprus [25], and form together with olive trees the basic constituents of the habitat type 9320 (Oleo-cerato- nion—olive tree and carob tree forests) of Annex I of the Habitats Directive (92/43/EEC). The carob tree is an entomophilous species, mainly pollinated by flies, bees, and wasps but is also wind-pollinated, depending on the habitat [26, 27]. Diurnal and nocturnal entomophi- lous pollinators visit carob flowers [26]. However, scarce information exists on the contribu-

tion of wild bee species to carob pollination, as well as on the importance of carob flowers to wild bee species. Dafni et al. [26] reported two unidentified wild bee species visiting carob flowers, and a few other studies refer to Apis mellifera as a key carob tree pollinator [28–30]. Cyprus hosts 369 bee species [31], but no data exist on their importance to carob pollination. Furthermore, there is no information on the contribution of pollinators to carob production. The current work aimed at assessing the contribution of insects to carob pollination towards yield efficiency and at documenting the diversity of wild bees in carob groves. Materials and methods Bee presence-absence study The bee presence-absence study was conducted in the following distinct carob growing regions: (1) North-West Coast (Polis Chrysochous area), (2) the South Plateau (Anogyra area) and (3) the South Coast (Zygi area) in 2016 (Fig 1). NW Coast and the S. Plateau were addi- tionally used for sampling in the 2017 growing season. The three regions represent different PLOS ONE Biodiversity and the impact of pollinators on carobs PLOS ONE | https://doi.org/10.1371/journal.pone.0291431 October 20, 2023 2 / 16