Inside or out: insect foraging behavior drives trade-offs between berry number and berry size in highbush blueberry.

Highbush blueberry (Vaccinium corymbosum L.) depends on insect pollinators, but frequently experiences pollination deficits, which limit crop yield and quality. Understanding the relationship between pollinator traits and pollination efficiency and their relative importance for pollen transfer, can provide valuable insights into how different foraging strategies influence pollination success. This study aimed to determine the influence of bee foraging behavior, specifically whether bees forage inside or outside the corolla, on pollination efficiency and fruit production in highbush blueberry. Fieldwork was carried out in 5 commercial blueberry orchards in southern Chile over 2 yr, where we recorded 893 flower visits from 16 species of bees. We classified pollinators into 2 behavioral groups: inside flower foragers (smaller-bodied native bees that enter the corolla) and outside flower foragers (larger-bodied bees that forage from the flower exterior). Using a single-visit pollination test and generalized linear mixed models, we quantified fruit set, fruit weight, and seed set by the 2 different foraging behaviors. Our results indicate that inside flower foragers significantly increased fruit set compared to unvisited flowers and outside flower foragers. However, outside flower foragers contributed more to fruit weight and seed set, highlighting a trade-off between pollination quantity and quality. This suggests that foraging behavior, rather than species identity alone, can serve as a predictive functional trait for pollination efficiency in blueberries. The behavior of foraging inside/outside the flower can serve as a functional trait to evaluate pollination efficiency, providing a new perspective beyond traditional species-level taxonomic identification.