Pg. 25-26 Pollination and Fruit-Set in Litchi: Final Report

Honeybee foraging activity in a litchi orchard was monitored by investigating returning foragers for nectar, water, pollen and bee-glue. At commencement of flowering 22 beehives were introduced into a 10 ha orchard. Both nectar and pollen were collected throughout the day from litchi florets, as well as during the entire flowering period. Water was collected mainly in the afternoon, on some days only. No bee-glue was collected during the period investigated.

In a second experiment in which fruit-set was studied, 400 panicles were marked on 20 trees and left open. A second set of 400 panicles was bagged with 1 mm² gauze to exclude insects. A mean number of nine fruits (range 0 – 44) per open-pollinated panicle was recorded, compared to less than one fruit per bagged panicle. The mean weight per fruit was 10 g per fruit for open panicles.

Summary:

• The study monitored honeybee foraging in a litchi orchard, focusing on their collection of nectar, pollen, water, and absence of bee-glue during the flowering period.
• 22 beehives were introduced into a 10 ha litchi orchard at the start of flowering to improve pollination and honey production.
• Honeybees collected nectar and pollen throughout the day and flowering period, with water collection mainly in the afternoons; no bee-glue was collected.
• Fruit set was studied using 400 open panicles and 400 panicles bagged with 1 mm² mesh to exclude insects.
• Open-pollinated panicles averaged nine fruits per panicle (range 0-44), while bagged panicles averaged less than one fruit.
• Mean fruit weight was about 10 g per fruit for open panicles.
• Litchi flowers have different flower types on the same tree, including male florets with no ovary, imperfect hermaphrodite florets with non-dehiscing anthers, and imperfect hermaphrodite florets with closed stigmatic lobes.
• Pollen viability varies with the stage of male florets.
• Low and irregular litchi yields have been linked to either failure to initiate flowers or failure in fruit set/retention.
• Although litchi cultivars are self-compatible, active pollen transfer (pollination) is required, mainly by insects.
• Various insects visit litchi flowers for nectar; honeybees are the most common visitors.
• Pollination by insects, mainly honeybees, significantly increases fruit set compared to self-pollination.
• Honeybee foraging activity peaked in the morning for nectar and around noon for pollen, declining in the late afternoon; water foraging increased later in the day.
• No propolis collectors were observed.
• Fruit set confirmation showed 95% of bagged panicles set no fruit, demonstrating limited self-pollination capability.
• Litchi relies primarily on insect pollinators, with honeybees being crucial; other potential pollinators include mopani bees, small carpenter bees, and certain flies.
• Insect diversity and abundance can be affected by environmental factors like cold winters, which impact pollinator activity.
• The importance of considering pollinator cold tolerance is emphasized in pollination management programs for litchi.