First report of the comparative effectiveness of insect visitors for cranberry pollination and yield in Chile

Biotic pollination sustains not only key ecological processes but also improves fruit set and fruit quality in pollinator-dependent crops like cranberries (Vaccinium macrocarpon). Distinguishing the subset of pollinators among floral visitors and combining this information with their frequency in flowers is essential for optimizing pollination services in cranberry crops, which improves fruit set through biotic pollination and overcoming the limitations of self-pollination. However, the relative contribution of different pollinator taxa to cranberry agricultural outcomes is entirely unknown in the Southern Hemisphere. Therefore, we compared the pollination performance and contribution to fruit yield of different floral visitors in commercial Chilean cranberry fields. Additionally, we sought to determine whether the sexual phase of the flower, mediated by dichogamy and herkogamy, co-influences pollination effectiveness. We assessed the performance of pollinators based on single-visit tests and their subsequent outcomes, such as fruit set, weight and viable seed set. Visit frequency was also recorded through 10-minute observations taken at five intervals throughout the day, in three cranberry orchards in southern Chile. Pollination performance and visitation frequency varied significantly between groups of flower visitors. The honey bee, the most frequent floral visitor, significantly increased fruit set compared to unvisited control flowers. Notably, the positive effect of honey bee visits on the fruit set is also reflected in fruit quality parameters, such as fruit weight or viable seed number. Despite their high frequency of visitation to cranberry flowers, flies demonstrated low pollination efficiency. Although no significant effect on fruit set was detected in relation to the temporal separation of staminate and pistillate phases, a pronounced effect on fruit quality was observed. Flowers visited by insects during the pistillate phase produced significantly heavier fruits and more viable seeds than unvisited flowers. While various insects visited the cranberry crops in southern Chile, only the honey bees significantly increased fruit set and weight and viable seed set. Synchronizing pollinator activity with the female receptive phase is important for effective pollen transfer and maximizing fruit quality. Promoting pollinator stability and diversity may optimize pollination services and ensure resilient crop production in changing agricultural landscapes.