Re-evaluation of the roles of honeybees and wind on pollination in avocado

Avocado (Persea americana Mill.) flowers, with their synchronously dichogamous behaviour, are considered to be pollinated by honeybees, despite the lack of any direct evidence. Results in southern Florida showed that avocado pollen was transferable by wind, and was dispersed over a brief period of time (15 - 60 min) each day. Ten 'Hass' avocado orchards in the Santa Clara River Valley, CA, USA, planted far from any known 'Zutano' polliniser trees, were selected to investigate the impact of honeybees on pollen transfer. 'Zutano' pollen (5 g per insert) was placed at the entry to beehives (approx. eight beehives per orchard) and refreshed four-to-five times during the flowering season. Successful pollinations were determined by parental analysis of harvested 'Hass' fruit from trees located at various distances from the beehives, and at three different stages of fruit development, using microsatellite DNA markers. The results showed no significant difference in the proportions of 'Zutano'-pollinated fruit with respect to distance and/or development stage between orchards provided with beehives containing 'Zutano' pollen and those without supplemented pollen. This strongly suggests that honeybees are not the major pollinators of avocado, and that most avocado flowers are self-pollinated by wind.