Pollination dynamics and bee foraging cycles in a tropical squash field

Temporal changes in the composition and abundance of floral visitors during floral anthesis influence the rate of deposition and germination of pollen in stigmas, as well as the rate of removal of pollen from anthers. In the tropics, the squash (Cucurbita pepo) is visited by a great diversity of bees, but little is known regarding the dynamics of its pollinators and pollination during its floral anthesis in tropical environments. We studied the foraging cycle of different species of bees in squash crops in Costa Rica and the relationship of this cycle with nectar production, pollen loads in anthers and bees, and number of pollen grains and pollen tubes in stigmas and styles. It was determined that despite the short duration of the floral anthesis of this crop, there are changes in the composition of visitors during anthesis from bees with twilight flight capacity that visit male flowers in the opening to primarily social bees at later hours. Loss of pollen from anthers and deposition of pollen on stigmas occurs rapidly in early hours. Pollen transport by bees may be facilitated by pollen accumulation at the bottom of the corolla of male flowers. After 6 a.m., little change occurs in crop pollination levels. The dominance of stingless bees in the flowers after 6:30 a.m. appears to displace other bees from these flowers, despite the permanence of nectar flow. The Cucurbita species may be an important crop for maintaining bee diversity and enhancing the pollination of other crops in agricultural ecosystems.