“Pollination by honey bees significantly increases the fruit set and yield of ‘self-fertile’ almond varieties”,  the conclusion of a study published in Nature Scientific Reports(1) earlier this year. 

The self-fertile (sometimes referred to as self-pollinating) almond variety ‘Independence’ was first introduced in 2008 and represented a major breakthrough for the almond industry in its bid to reduce dependence on honeybees for pollination. New orchard planting increased significantly following its launch and it now represents about 5% of the total California almond bearing acreage. 

However, to date, there has been a lack of data about the true pollinator dependence of this fast-growing almond variety. The research, carried out in Kings County California in 2018, showed that Independence trees did produce nuts when bee visitation was curtailed, but that honey bee visits increased the yield substantially. Fruit set was 60% higher, which translated into a 20% increase in kernel yield. Furthermore, the yield increase translated into a 10% increase in net profit (i.e. after colony rental costs). There was no evidence that bee visitation affected the nutritional quality of the Independence almonds, although other studies have shown that cross-pollinated almonds have higher nutritional quality, in terms of fat composition than self-pollinated almonds(2).

The orchard used in the experiment was planted with 50%/50% Nonpareil - Independence tree varieties and honey bee colonies were placed at 2 colonies/acre as part of the normal commercial pollination management arrangement used by the grower.

Figure 1: Aerial images of the experimental setup showing trees isolated from bees (Photo credit Sáez, A., Aizen, M.A., Medici, S. et al. Bees increase crop yield in an alleged pollinator-independent almond variety. Sci Rep 10, 3177 (2020). https://doi.org/10.1038/s41598-020-59995-0)

While the research proved conclusively that honey bee pollination profitably increases the yield of Independence variety almonds, it did not estimate the optimal number of bees required. In the study, the orchard was stocked with the industry standard 2 hives per acre. However single variety orchards of self-fertile trees should require fewer bees to achieve adequate pollination than traditional orchards where pollen needs to be transferred between multiple varieties. 

Experience of growers to date and the published guidance that is available has suggested 0.5 hive – 1 hive per acre could be sufficient(3)(4)(5). However, these recommendations are based on anecdotal evidence. Also, much depends on the size of the orchard and the surrounding planting - those surrounded with traditional almond varieties will have greater exposure to bees.   

This study has shown that honey bee pollination is a vital input for self-fertile almond varieties. While these varieties should enable growers to decrease hive stocking rates, further investigations are required to determine the precise number of bees required for growers to optimize yields and profits. 

1. Sáez, A., Aizen, M.A., Medici, S. et al.Bees increase crop yield in an alleged pollinator-independent almond variety. Sci Rep 10, 3177 (2020). https://doi.org/10.1038/s41598-020-59995-0

2. Brittain et al Pollination and Plant Resources Change the Nutritional Quality of Almonds for Human Health; PLoS ONE February 2014

3. Doll D. Independence Almonds - Some Observations. The Almond Doctor June 30, 2012

4. Parsons C. A closer look at the self-fertile Independence almond variety. FarmProgress June 14, 2017

5.  Almond Board of California Honey Bee Best Management Practices for Almonds, 2018 Edition