Improving bee performance

Published on August 30, 2023

Research & Extension

Gordon Brown reviews a method of ‘training’ bees to selectively harvest nectar and pollen from apple and pear orchards.

Reliable high yields of apple and pear orchards are essential to ensure the economic viability of orchards into the future. High yields start with pollination, which is dominantly performed by honey bees with some assistance from wild bees. In order to ensure good pollination it is necessary to install honey bee hives in the orchard. Unfortunately, sufficient honey bee hives are not always available so methods of ensuring high efficiency of available bee hives is essential.   

Method

Walter Farina has been studying honey bees for over 20 years and in recent research has been developing methods of training bees to preferentially collect nectar from target crops. The method involves studying the literature for known volatile compounds emitted by the crop flowers and then selecting some of these that bees respond to. This is done by placing a small drop of an aroma compound produced by the flowers onto the antenna of a bee and observing the proboscis reflex to determine the most responsive aroma compounds. For pears he has patented a mixture of 24 per cent limonene, 35 per cent linalool and 41 per cent α-pinene (US20200205404A1 patent documentation) and for apples it consists of 44 per cent citral, 40 per cent benzaldehyde and 16 per cent limonene (WO2013005200A1 patent documentation).  

For these trials, 50µl of the above mixtures were added to a litre of 50 per cent sucrose solution. For apples, 1.5 litres of the sugar aroma mixture was placed into each hive for 2 days, about 3 days before the beginning of blooming and about 9 days before full bloom. For pears, 500ml of the solution was spread over the top of the central frames when trees were at about 10 to 40 per cent bloom and 5 to 7 days before full bloom. In the orchards, plot size tended to be around 4ha each, with about 16 hives. Each ‘sugar plus aroma’ fed plot had a ‘sugar only’ fed plot in the same orchard. A total of eight trials were carried out on two different orchards covering Gala, Red Delicious, Hi Early, Granny Smith and Chañar 28 apple cultivars, as well as Williams, Packham and D’Anjou pears. 

Measurements 

Hive incoming bee activity was measured in the morning from 3 to 9 days after feeding, and pear pollen loads were collected for the period from 3 to 8 days after feeding. Fruit set as the number of fruit per tree was measured and commercial apple yield was recorded by the grower. 

Results

Bee activity 

For apples, the sucrose plus apple flower aroma treatment increased the activity of bees pollinating trees in the mornings during full bloom compared to bees fed sucrose alone (Figure 1). This indicates that the feeding of sucrose plus apple flower aroma caused the bees to learn to associate apple flower aroma with nectar such that, when they sensed the apple flowers in the orchard, bee activity increased and they targeted apple trees for their nectar.  

The situation with pears is more complicated, possibly because pears do not produce much nectar and, as a result, bee activity in pear orchards is dominantly for the collection of pollen. In the trial that studied bee activity in the morning, the hives primed with sucrose plus pear flower aroma did not seem to be quite as active. It may be that priming bees with sucrose did not stimulate bees that specialise in pollen collection. Alternatively, other research (see further reading) has shown that pear flowers shed pollen predominantly in the afternoon such that the priming of the hives may not lead to increased activity till the afternoon. The trial concerning pear pollen collection at the entrance to the hive occurred at a different location and, while still in the morning, may have occurred later in the day. These results in Figure 2 show an increase in pear pollen collection in the primed hives, indicating improved pear pollination. 

Fruit set and yield 

For both apples and pears an increase in the number of fruit per tree was observed. For apples there was a 40 per cent increase in the number of fruit and for pears there was an 18 per cent increase (Figure 3). The authors are bee researchers and this was their focus; no reason was given for the overall low numbers of fruit per tree in the trials. They do tell us they counted the number of fruit on 30 trees around each treatment, adjusting for trees that had no fruit. This suggests that the orchards were subject to biennial bearing and were in an ‘off’ year. 

No data is provided for the yield of pear fruit from the trials, although the commercial yield of apples harvested by the grower at one of the sites (where trees without flowers were noted) is provided (Figure 4). This identified that in this poor fruiting season the yield of fruit was doubled from 14t/ha to 28t/ha, demonstrating the massive impact of feeding bees with sucrose plus apple flower aroma compounds 3 days before flowering on commercial yield. 

No data was provided on seed numbers per fruit, fruit size or any other fruit quality measurement. 

Take home messages 

• These trials were conducted in a low yielding orchard, possibly in an ‘off’ fruiting year. 
• Feeding bees with a 50 per cent sucrose solution with apple or pear flower aromas added at the start of flowering dramatically improved fruit set in both apples and pears, and doubled the yield of apples in this trial. 

Further reading 

Farina W, Arenas A, Diaz P, Susic Martin C and Corriale M (2022) ‘In-hive learning of specific mimic odours as a tool to enhance honey bee foraging and pollination activities in pear and apple crops’, Scientific Reports, 12:20510. www.nature.com/articles/s41598-022-22985-5 

Farkas A, Orosz-Kovács J,  Szabó LG, Bubán T (2000) ‘Floral attractivity of pear cultivar Cinderi’, International Journal of Horticultural Science, 6(1):102–109 https://ojs.lib.unideb.hu/IJHS/article/view/78  

This article was first published in the Winter 2023 edition of AFG.

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