Assessing the biodiversity and the impact of pollinators on carob production

brevigena was collected from March to December, C. cyprius from February to October while H. imparilis from April to October, with the latter two periods falling outside carob blooming [31]. Five species of wild bees are associated with carob pollination for the first time: A. bicolor, A. rufitibialis, A. vulpecula, H. taeniolatus and Lasioglossum sp.. C. brevigena seems to rely heavily on carob flowers as well as neighboring habitats, as it was very common in all regions in the current study and was recorded from carob trees in several regions both during and out- side the carob blooming period in the past [31]. Wasps were the third most frequent visitor to carob flowers but very few studies refer to them as carob tree pollinators. Dafni et al. [26] recorded very few individuals from two species of wasps, Vespula germanica and Vespa orientalis, while Arista et al. [44] recorded a high rate of visits (79%) of Vespula sp. Al-Ghzawi et al. [45] recorded V. orientalis and Polistes dominu- lus in small numbers but their contribution to carob tree pollination was small and unreliable. An earlier study found that male carob trees were more attractive to A. mellifera and wasp species than female trees, due to pollen production [30], in agreement with the findings of the current work. Visits to flowers of male trees were much more frequent than to flowers of female trees. Male trees are more attractive to insects probably because they provide both pol- len and nectar, while female trees provide nectar only, even though female flowers produce a

higher volume of nectar with higher sugar content than male flowers [30]. Volatiles emitted by male and female flowers also differ [26]. We note that the visitation rates to male and female trees in the current study are not directly comparable, as in carob groves female trees are found at a much higher density than male trees (ca. 10 female: 1 male). However, there is a strong trend of preference for male versus female flowers by the insect species studied in the Fig 6. Presence (1) or absence (0) of pollen in pollen traps placed on one male (distance = 0 m) and five female trees. Four pollen traps were placed in each tree for a 24-hour period. Random vertical jitter was added to allow visualization of all data points. See Materials and Methods for more details on the methodology. https://doi.org/10.1371/journal.pone.0291431.g006 PLOS ONE Biodiversity and the impact of pollinators on carobs PLOS ONE | https://doi.org/10.1371/journal.pone.0291431 October 20, 2023 11 / 16