Pollination ecosystem services to onion hybrid seed cropsin South Africa

[摘要] ENGLISH ABSTRACT: Insect pollination contributes in various degrees toward the production of a variety ofagricultural crops that ensure diversity and nutritional value in the human diet. Althoughmanaged honeybees (Apis mellifera L.) are still the most economically valuable pollinators ofmonoculture crops cultivated globally, wild pollinator communities can contributesubstantially toward crop pollination through pollination ecosystem services sourced fromneighbouring natural habitats. Pollination ecosystem services are thus valuable and canmotivate for the protection of natural ecosystems hosting diverse insect pollinatorcommunities. F1 onion hybrid seed production is entirely dependent on high insect pollinatoractivity to ensure cross pollination, seed set and profitable seed yields. Data was collected on18 onion hybrid seed crops grown in the semi‐arid Klein Karoo and southern Karoo regions ofthe Western Cape, South Africa. These two main production regions are located within theSucculent Karoo biome, recognized as a global biodiversity hotspot of especially high plantdiversity. It is also habitat to the indigenous Cape honeybee (Apis mellifera capensis Esch.).Sites selected varied in the percentages of available natural habitat and managed honeybeehives stocking density. Diverse anthophile assemblages were sampled with pan traps withinall the onion fields, regardless of the percentage of available natural habitat near the crop.Crop management practices significantly affected the diversity of anthophile species caughtwithin onion fields, although less than 20% of this diversity was observed actually visitingonion flowers. The honeybee (managed and wild) was by far the most important pollinatorbecause of its high visitation frequency and regular substantial onion pollen loads carried ontheir bodies. Honeybee visitation significantly increased onion hybrid seed yield, whileanthophile diversity and non‐Apis visitation had no effect on seed yield. Neither managedhive density, nor percentage natural habitat were important in determining honeybeevisitation or seed yield. Total annual rainfall was the only significant factor determininghoneybee visitation. Secondary factors caused by rainfall variability, such as wild flowerabundance or soil moisture, may have significantly affected honeybee visitation. In addition,the positive correlation between honeybee visitation and the diversity of hand‐sampledinsects from onion flowers; indicate that either or both onion varietal attractiveness and/orpollinator population size may have had significant effects on overall insect visitation.Honeybees showed marked discrimination between hybrid onion parental lines and preferredto forage on one or the other during single foraging trips. Hybrid onion parents differedsignificantly in nectar characteristics and onion flower scent which would encourage selectiveforaging through floral constancy. Interspecies interactions were insignificant in causing increased honeybee pollination because of the scarcity of non‐Apis visitors. Most farmingpractices are subjected to favourable environmental conditions for successful production.However, and especially in the South African context, the dependence of onion hybrid seedcrops on insect pollination for successful yields, increase its reliance on natural ecosystemdynamics that may deliver abundant wild honeybee pollinators, or attract them away fromthe crops. Nevertheless, this dependence can be mitigated effectively by the use of managedhoneybee colonies to supplement wild honeybee workers on the flowers.

[发布机构] Stellenbosch University