Pollination Research

 

Almonds

Almonds, Prunus amygdalus, are mainly planted in the Western Cape, but new cultivars are planted in other areas of the country. Currently there are more than 550 hectares plated in South Africa.

The individual trees flower for about 21 days. Most cultivars are self-incompatible and a compatible polinizer cultivar is planted within the main production cultivar orchard. The flowers are most receptive for pollination on the second open day. Honeybees play an essential role in the cross-pollination of cultivars for a better quality crop. Research Results

A study on almond pollination was conducted during August and September 1989 near Loskopdam in Mpumalanga. The high density 3 ha. almond orchard established in 1985, consisted of the cultivars 'Ne Plus Ultra' and 'Pearless' in the ratio 2:1. The test orchard was adjoin by a further 4 ha. of almonds and 30 ha. of peaches. The rest of the farm was used for cattle and pasture and uncultivated fields were within the forage rage of the test colonies. The two most promising competitive wild plants were Aloe grayhedii var. davyana, and Aloe marlothii.

Honeybee activity remained constant during the day with an average of 6 bees per tree. Activity however decreased from an average 8 bees per tree at 50-60% bloom, to 5 bees per tree at full bloom.

The final fruit set was determined 40 days after flowering and the following results were obtained:

1. Flowers where pollen was not available from the pollinizer had an average fruit set of 1%.

2. Flowers where pollen was available from pollinizer had an average fruit set of 10%.

3. Insignificant differences were found in fruit set on the eight wind directions indicating good pollen movement by the pollinators.

A pollen trap was fitted to one hive. Pollen trapped with this method was identified with the aid of a light microscope to determine the major foraging plants in the study area. The results are given in a table:  

The results show that although alternative nectar and pollen sources can attract foragers away from almonds, successful cross-pollination can be achieved.

In another test, a bee attractant was applied and an increase of 50% in fruit set was achieved.

Pollination Requirements

It is recommended that 5 -8 hives per ha is placed in or near the orchard when both target and polliniser cultivar are at 50% flower. Competitive plants should be removed. 

Apples

The apple, Malus domestica, is mainly planted in the Western Cape, but new cultivars are becoming increasingly popular in other areas of the country. In South Africa more than 22 500 ha are already under cultivation.

The individual trees flower for 10 to 25 days. Most cultivars are self-incompatible and a compatible polliniser cultivar is planted within the main production cultivar orchard. Honeybees play an essential role in the cross-pollination of cultivars for a better quality crop.

The plant produces a nutritious pollen and fair quantity of nectar but colonies strength usually decline because of pollination overstocking.

Research Results

Returning foragers collected at the hive entrances from colonies placed in an apple orchard showed that within three days of being placed in the orchard some foragers collected less than 5% apple pollen. It is therefore imperative that the beekeeper introduces his pollinating bees only at optimal blossom time, and to eliminate all alternative forage plants.

Recommendations

For good pollination 2-5 hives/ha is recommended. Good tree coverage by bees is achieved if 3 or more bees per tree at any time of the day are counted. 

Avocado

Pollination and fertilization of avocado, Persea americana, are prerequisites for fruit set and fruit development receptively. In South Africa avocados are planted on more than 14 800 ha, with a projected growth of 5% annually. A total of 81 000 tones of fruits were marketed in 2001 with 55% of the crop been exported.

Some avocado cultivars are self-incompatible i.e. fertilization can not take place with pollen of the same cultivar. Well-known cultivars such as 'Hass', 'Feurte', and 'Ettinger' are, however, self-compatible (they can be polinated by pollen from the same cultivar). As avocado is not wind-pollinated it requires active transfer of pollen by insects. Bees are by far the best pollinators because they actively collect nectar and pollen, and their hairy bodies are effective pollen carriers.

In different surveys it was found that the number and diversity of insects that visit avocado flowers varies from one orchard to another, and from one season to another.

Competitive bee-plants can lure bees away. Examples of these include blackjacks, late flowering saligna gums in some years, or early flowering citrus.

 
Research results

Honeybee foraging activity was investigated in a 50 ha orchard (cv. Hass and Ryan) at Politsi near Tzaneen in the Northern Province. Foragers returning to the hive were examined for nectar-, water-, pollen- and propolis loads. No single foraging activity dominated during any time of day or during the flowering period, indicating that neither pollen nor large volumes of nectar were available in large quantities. Returning foragers sampled at the hive entrance throughout the day that carried avocado pollen did not collect mixed pollen (of other plants) and were therefore specific in their preference. Avocado flowers proved much more attractive to honeybees than mango and litchi.

To test the value of insect pollination, all insects were excluded by enclosing inflorescence (flower panicles) with fine mesh bags. Whereas 400 bagged inflorescence yielded only two fruits, an equal number of marked but open inflorescence yielded 33 fruits, proving the importance of insect pollination.

Botanical, entomological and horticultural aspects were combined to study the influence of the pollen donor 'Ettinger' and bees on 'Hass' yields and fruit size. The experiment was carried out in a four-year-old 'Hass' orchard bordered by a row of 'Ettinger'. To study the role of pollinators cages that excluded all insects were erected over groups of trees consisting of the pollinizer and crop cultivar. In one group honeybee colonies were placed inside the cages to determine the value of honeybees as pollinators. Fruit set in caged trees with bees was significantly higher than in those without bees. 'Hass' flowers pollinated with 'Ettinger' pollen produced larger and heavier fruit. Honeybees did not only increase the crop but due to cross-pollination better quality fruits were produced.

To determine the distribution of honeybees in a commercial avocado orchard in which every tenth row was a pollinator cultivar, a new method was applied using fluorescent powder to mark outgoing foragers. During the evening, a portable UV light was used to scan inflorescences for deposited powder. The number of visited inflorescences declined with increasing distance from the hives, up to 300 m along rows of trees. The survey across the rows of avocado trees and casuarina windbreaks yielded significantly fewer visited inflorescences, the furthest being only 200 meters from the hives. This shows that to optimise pollination, colonies should not be more than 150m apart.

Recommendations

The number of colonies required for effective pollination varies from 2 to 4 per hectare. To establish whether there are enough bees present to give adequate pollination, the number of bees foraging on the flowers should be counted between 10 AM and 12 noon on a fine day. This should be repeated between 2 PM and 4 PM. The timing is important because it is at these times that the flowers produce nectar and pollen optimally. Five bees per squire meter of flowering canopy tree area, or five bees per twenty inflorescence indicate that an adequate number of foragers are present in the orchard. 

Canola

Canola, Brassica napus var. oleifera, is a member of the cabbage family. It is mainly planted in the south-western Cape for its oil and, on small scale, for seed production in the Free State and northern Cape.

The crop flowers for 5-7 weeks. The flowers are self-compatible, but the quality and quantity of seeds are greatly increased by honeybee pollination.

The crude protein content of canola pollen is high, stimulating rapid brood production and swarm build-up that often leads to swarming. In the south-wetern Cape when the old queen departs Capensis laying workers may take over resulting in considerable colony losses. Less or weakened colonies also means honey crop losses.

Recommendations

It is recommended that 2-6 hives/ha is used. Honey must be extracted as soon as possible because conola honey crystallizes quickly in the comb.   

Commercial crop pollination

Pollination services rendered by beekeepers create direct jobs for thousands of people, but the secondary role it plays as job creator in farming, packing, manufacturing, marketing etc. touch the lives of hundreds of thousands of people in South Africa.

Pollination services rendered by beekeepers create direct jobs for thousands of people, but the secondary role it plays as job creator in farming, packing, manufacturing, marketing etc. touch the lives of hundreds of thousands of people in South Africa.

Estimated value of honeybees in commercial crop pollination in South Africa

Although each crop to be pollinated has different pollination requirements there are general rules and standards for pollination units that should be adhered to.

Litchi

Litchi, Litchi chinensis, is mainly planted in the subtropical regions of the country. It is estimated that there are more than 1000 ha planted. The trees bear three flower types on the same tree: male, female and bisexual, the ratio varying with cultivar and season. The honeybee is the most important pollinator. A tree flowers for up to 21 days.

Research results

Honeybee foraging activity was investigated in a 10 ha orchard (cv. Bengal) at Politsi near Tzaneen in the Northern Province. Foragers returning to the hive was examined for nectar-, water-, pollen- and propolis loads. Nectar foraging dominated throughout the day, and only small quantities of pollen were collected by the foragers.  

The flowers panicles (inflorescence) of some trees were bagged in fine mesh bags to exclude insect pollinators. It was found that 95% of bagged panicles did not set any fruit. Less than one fruit per bagged panicle matured. In contrast, 92% of open (mainly honeybee) pollinated inflorescence bore fruit, with a mean of 9 fruits (range 0-44) per panicle, indicating the importance of insect pollination.

Recommendations

It is recommended that 2-4 hives/ha are placed inside the orchard. Colony strength increases which can cause the colonies to become more defensive. Therefore, the colonies should not be placed where farm personnel often pass. 

Mango 

The mango, Mangifera indica, originates from India. The fibreless mango cultivars 'Haden', 'Alphonse', 'Paheri', 'Mulgoba', and 'Totafari Gren' were introduced in South Africa between 1920 and 1930. More extensive plantings took place after 1960 with the introduction of 'Kent', 'Keitt', 'Tommy Atkins' and 'Zill'. Mangos are ranked as the fifth most important subtropical crop in South Africa, after citrus, banana, avocado and pineapple. The total area under production is more than 8000 hectares. The largest growing areas are Hoedspruit, Malelane, Letsitele Valley, Deerpark, Lower Letaba, Trichardsdal, Ofcolaco, Hazyveiw, Levubu, Louis Trichardt, and Mooketsi.

The 1995/'96 crop was approximately 45 000 tons of which 13% were exported, 26% locally marketed, 44% sold for achar processing, and 9% sold for juice processing. The value was estimated at R77 500 000.

The crop flowers for approximately 28 days. Pollen grain development in both male and female flowers is affected by climatic conditions. Cold spells during pollen development result in low pollen viability and hamper successful pollen tube growth after pollination. Flowers usually open in the early morning, but temperatures above 20 °C are required for anther dehiscence and pollen shed. High humidity affects this process negatively. Certain cultivars have far less pollen than others do. The stigmas remain receptive for at least 6 hours, although if not pollinated, receptivity can last up to 3 days. Both male and female flowers can produce nectar.

Research Results

Returning foragers were examined for nectar, water, pollen and propolis loads in a 14 ha. orchard (planted with cultivars Kent and Keitt) in the Letsitele Valley in the Northern Province. Mango flowers secreted little nectar. However, bees collected nectar from extra-floral nectar-glands situated at the bases of the panicles throughout the day. This ensured that foragers returned to the target crop throughout the flowering period. Small amounts of pollen were available for the bees to collect from the single viable stamen of each flower. Foragers visited the flowers throughout the flowering period despite some competitive nectar and pollen sources in the vicinity, indicating forager specificity. Foragers made contact with both anthers and stigmas in search for forage and thus effectively pollinated the flowers.

In testing the influence of insects (but especially honeybees) as pollinators, 400 bagged inflorescence yielded no fruit while 400 open marked inflorescence produced 6 fruit. Natural fruit-drop was high and this explained the low number of fruits that matured.

Recommendations

Pollination recommendation is 3-15 hives/ha. Colony strength decline during the pollination period and therefore strong and healthy pollination units are required. Competitive plants should be eliminated. 

Onions

Pollination for seed production of onions, Allium cepa, is practiced mainly in the Northern and Western Cape provinces. Pollination occurs when pollen is transferred from the dehiscing anthers of one floret to a receptive stigma of another floret. Effective transfer of pollen between florets on an umbel or between plants must transpire through the action of an outside agent because self-pollination is almost impossible. In hybrid seed production, a pollinizer cultivar is planted amongst male-sterile plants, and insect pollination is essential.

The crop flowers between 25 and 30 days. The flowers have nectar and pollen, but attractiveness is generally low, which can be aggravated by lack of plentiful soil moisture, fertilization with phosphorus and nitrogen, potassium in nectar, and beeplant competitors.

Recommendations:

It is recommended that 5-12 hives are used per hectare. To ascertain whether there are enough bees in the field for adequate pollination, bee cover of 100 bees per 30m male fertile plant row, and 40 bees per 30m male sterile (female) row is satisfactory.

The banded bee pirate, Palarus latifrons, is a predatory wasp that may cause problems in sandy soil areas.  Bees prefer not to collect nectar from flowers where the potassium content in the nectar is higher than 8000 p.p.m.  

Plums 

The plum, Prunus domestica, is mainly planted in the Western Cape. It is estimated that 4 600 ha are in production in the country. Honeybees are important pollinators because new cultivars are mostly self-incompatible and therefore require compatible pollinisers. Individual trees flower between 8-14 days. The stigma of a flower is receptive for 1-2 days before the anthers of that flower dehisce. The flowers secrete nectar with a low sugar concentration. The amount of nectar secreted varies between cultivars.  

Research results:

In the Western Cape the pollen loads of returning foragers from the plum cultivar 'Songold' was collected and the ratio of plum pollen to other plants determined. Plum pollen was not collected in large quantities, indicating that it was not very attractive to the bees. Large numbers of commercial colonies are therefore needed to supply enough bees for satisfactory pollination of this crop. Flower bearing branches were covered in a fine mesh bag to excluded insects from pollinating the flowers. The covered branches yielded very view fruit, indicating the importance of honeybees as pollinators.  

Recommendations:

It is recommended that 2-6 hives/ ha be used to supply good tree coverage by bees. Pesticide spraying may cause honeybee mortality and should be avoided by either closing the hives or moving the colonies out of the orchard during spraying.  

General Guidelines and Pollination Standards

Colonies used for pollination must be queen-right, have at least 8 brood frames cocered with bees and 4 brood frames with brood of different stages. For most crops colonies can be moved into the orchard or field when flowering is at approximately 10% (i.e. 10% of all flowers have already opened). Colonies should be placed in groups, preferably forming a circle to limit drifting. One site should be no more than 400m from the next. If this can't be done, they should be placed along the edge of the orchard or field. When the colonies are placed in a line it is best to stagger them as much as possible and turn every second entrance 180°.

The colonies must be protected against ants. If there are competitive bee-plants in or near the orchard, increase the number of colonies, or if possible remove the plants.

Supplying fresh water is essential throughout the year, because in winter there may be a shortage of natural water and in summer the colonies are hot and need more water to maintain the required humidity and temperature for brood rearing.