Assessing the biodiversity and the impact of pollinators on carob production

landscape types, with the NW Coast classified as settled cultivated coastal lowland, the South Coast as settled cultivated coastal alluvial plain and the South Plateau as settled agrosilvopas- toral plateau [32]. Carob groves were located at a minimum distance of 1 km from each other. One male and four female trees were sampled for each of the four carob groves in each region. None of the trees used in the presence-absence study were hermaphroditic. Most carob groves on the island contain a single male tree. Application of pesticides is very uncommon in carob groves, and no pesticide applications were made to the groves selected for the current work. Each carob grove was sampled weekly for five consecutive weeks during carob blooming on Julian days 294 to 323 in 2016 (October 21 to November 19, 2016) and 293 to 322 in 2017 (October 18 to November 20, 2017). Samplings were conducted between 08:30–12:30 in good weather conditions (sunny days, light breeze, without or slightly cloudy). For each tree, obser- vations were carried out for two min on each of the four cardinal sides of the tree (north, west, south, and east), resulting in a total of eight min per tree and 40 minutes per carob grove (five trees x eight minutes each). For each tree side, data regarding the presence-absence of A. melli- fera, wild bees and other potential pollinators (e.g. wasps, Diptera) were collected. Wild bee specimens representing different morphospecies were collected with a net and transferred to the laboratory for identification at the genus/species level. Carob pollination study

The carob pollination study was conducted in three carob groves, one each in the NW Coast (NW C 4), the S. Plateau (SP 1) and the South-East Lowlands (SE 1, Fig 1) in 2017. The groves in NW Coast and S. Plateau were selected among the ones used for the bee presence-absence study. The SE Lowlands region is classified as settled lowlands farmland [32]. Based on discus- sions with growers, the trees in NW C 4 and SP 1 belonged to the landrace Tillyria, while the Fig 1. Study sites for the bee presence-absence and carob pollination studies. Bee presence-absence study: North- West Coast–NW C1-4 green dots, South Plateau–SP1-4 red dots, South Coast–SC1-4 yellow dots. South-East Lowlands–SE1 brown dot. ArcGIS v.10.7 [33]. https://doi.org/10.1371/journal.pone.0291431.g001 PLOS ONE Biodiversity and the impact of pollinators on carobs PLOS ONE | https://doi.org/10.1371/journal.pone.0291431 October 20, 2023 3 / 16