A new pollination probability index (PPI) for pollen load analysis as a measure for pollination effectiveness of bees

Conventional pollen load analyses have calculated the proportion of pure to mixed pollen loads, or the average percentage of conspecific pollen on bees captured at their nests or hive. These indices can not distinguish ‘flower’ constancy from ‘pollen’ constancy, and are poor estimates for the probability of pollination. This study proposes a new index for pollen load analysis which reflects floral constancy at the pollinator population level and therefore may be an estimation for pollination probability (PPI). This index is the product of the mean proportion of conspecific pollen on bees captured on a certain forage flower species multiplied by the proportion of bees carrying that conspecific pollen. The PPI can be used to estimate the probability of pollination in natural plant populations as well as in crop plants. This study calculated the PPI for bumble bees foraging on five keynote species of a mediterranean phrygana: two polleniferous (Hypericum triquen-trifolium and Myrtus communis) and three nectariferous (Cephalaria joppensis, Echinops adeno-caulos and Salvia fruticosa) plant species which are the main food sources of Bombus terrestris under the local conditions.