Insufficient native pollinators during artificially induced early flowering decrease yield and long-term economic viability of a tropical fruit crop

Abstract

The management of crops outside the regular cropping calendar can improve profits when supply is low and prices are high, but we do not know how induced, early flowering impacts the pollination services that crops require. This study examines the effects of flowering time and pollinator management, including managed honeybee colonies and ground flower cover, on the pollination of the tropical fruit tree, longan (Dimocarpus longan Lour.), comparing between in-season flowering (naturally) and off-season flowering (chemically induced) in Northern Thailand. Visitation rates of flower visitor groups significantly differed among treatments: for in-season flowering, wild bees were the most frequent pollinator group, whereas in the off-season flowering, there were no wild bees, and instead dipterans were the most frequent pollinator group. Some off-season plantations have honeybee hives present and in this situation honeybees were the most frequent pollinator group. We show that temporal variation in the pollinator community significantly alters the pollination efficiency of longan crops. Consequently, longan production from off-season longan farms generates lower net profit in the absence of managed bees and wild bees, and wild bees produced higher seed-sets than either honeybees or dipterans. Synthesis and applications. Wild bees were the main pollinator group of longan in the in-season flowering resulting in high fruit production; whereas in the off-season flowering honeybees and dipterans were the main pollinator group. Longan production from off-season longan farms without managed bee produced less net profit. The farmers practicing off-season with honeybee hives management gain the largest net profit. Developing mechanisms to promote and maintain pollinator abundance and diversity is likely to increase the resilience of the system in addition to profit in the long term; thus, efforts should be made to provide more nesting habitat and reduce pesticide use.