Contribution of honeybees to white clover pollination in hill and high country grasslands under development in Otago

Abstract

Development of the hill and high country tussock grasslands of Otago (N.Z.) by aerial oversowing with legumes has been carried out on a large scale without concurrent research into the role of reseeding in the longevity of legume based pastures, or of the agents responsible for pollination. The present study focuses on (1) the level of pollination and seeding that occurs in hill country areas remote from apiaries, {2) how pollination levels can best be increased by the introduction of managed apiaries, {3) whether a honeycrop is available to the beekeeper to offset additional costs of operating in a more difficult environment, and (4) to identify some of the difficulties of high country beekeeping. In areas remote from commercial apiaries where no honeybees were found, pollination levels of approximately 20% were recorded. Low numbers of honeybees from non-experimental apiaries were found at most sampling sites, producing pollination levels generally between 20-30% and 2-3kg/ha of good seed. By manipulating insect access to white clover plots the maximum pollination level attainable by high densities of honeybees and bumblebees was found to be 97% and 95% respectively. Self pollination was thought to have caused between 1% and 7% pollination in cages where insects were excluded, and a high percentage of this seed was aborted. Very large increases in pollination and seed production were recorded following the introduction of an apiary to a hill country area remote from commercial apiaries. The pollinating range of honeybees from hill country apiaries was between 1km and 2km, and pollination levels declined with increasing distance from the apiaries. To maximise pollination, seed, and honey production it is recommended that 16-hive apiaries be spaced 2.5km-3km apart, depending on flower densities. Differences in pollination and seed production between sites with varying aspect were mainly caused by physical and climatic attributes of aspect influencing the timing and density of white clover flowering. A programme of pollen trapping revealed that pollen sources in high country areas may lack diversity and that pollen gathering can be restricted by unfavourable weather conditions in early spring. Pollen deficiency was identified as a probable cause of crop failure in hives overwintered in the high country for two consecutive winters. A programme of hive weighing showed that the honeyflow in high country areas can be very short, and can be curtailed by climatic conditions before the end of flowering. Honeycrop increases of up to 50% were recorded in high country apiaries at the expense of a 100% cost increase. Honeybees are necessary to produce high pollination levels in high country areas, however beekeeping in these areas is not economically viable at the present time.