Ecology of honey bee (Apis mellifera L.) pollination of kiwifruit (Actinida deliciosa (A. Chev.))

Abstract

The ecology of honey bee (Apis mellifera L.) pollination of kiwifruit (Actinidia deliciosa (A.Chev.)) was investigated by relating the floral biology of kiwifruit flowers to the foraging behaviour of the honey bees visiting them. Comparisons were also made of the behaviour of honey bees in orchards with high and low forager densities. By studing kiwifruit flowers it was found that most staminate and pistillate flowers open before anther dehiscence which occurs at about 0900 h. Both sexes of flower start to close again in the afternoon of the day they open. All the anthers dehisce on the first morning the flowers are open. The anthers on staminate flowers take three days to liberate all their pollen while anthers on the pistillate flowers take five days. Most of the daily pollen liberation occurs in the morning and early afternoon. Foragers visiting flowers on a tray discriminate between staminate and pistillate kiwifruit flowers and are generally constant to the sex of the flowers they are visiting. They show an overall preference for pistillate flowers which results in the collection of few staminate or mixed (staminate and pistillate) pollen loads when they are foraging in an orchard where there is little competition for pollen. The foragers show between trip flower sex constancy and some have foraging areas to which they return on consecutive trips. Foragers preferentially move along T-bar rows as opposed to between rows and only move staminate pollen small distances from staminate vines. Foragers visit few pistillate kiwifruit flowers over five days old and few staminate flowers over three days old. Full pollination of a kiwifruit flower by honey bees is the result of a large number of forager visits occurring over the five days the pistillate flowers are attractive to honey bees. In an orchard with a high forager density, the daily timing of kiwifruit pollen collection depended on the timing of kiwifruit anther dehiscence and the depletion of the pollen supply by the foragers in the afternoon. Foragers which stopped collecting kiwifruit pollen in the afternoon remained in the hive until the following day. The timing of the end of pollen collection in an orchard with a low forager density depended on either the pollen becoming too dry, or more likely on the colonies having met their daily pollen requirements. Feeding colonies sugar syrup inside their hive increased the time taken for foragers to find house bees to accept their nectar loads. Colonies in a kiwifruit orchard doubled the amount of kiwifruit pollen collected when they were fed sugar syrup. This resulted from an increase in the number of foragers visiting kiwifruit flowers rather than an increase in the length of time the flowers were visited during the day. A systems diagram of the factors that are related to kiwifruit pollination and affect fruit size has been presented. The direction of future research and the current recommendations for kiwifruit pollination have been discussed and extended.