Dr Saul Cunningham, CSIRO Ecosystem Sciences & Danny Le Feuvre, Australian Beekeeping Services,
• Bee density is a very poor predictor of what really matters, which is the frequency of cross-pollination events. The importance of cross-pollination (rather than density per se) is underlined by the pattern of poor nut set in the hive row, and by the pattern of better fruit set near edges. • Both the poor nut set in the hive row and the better nut set near edges make sense, but they both contribute to “washing out” the simple distance-from- hive effect we otherwise expected. • Because it was difficult to create truly low bee density in the blocks, all of our data might have been at a relatively high bee density. If we were able to reduce bee density further, we may have had more relationship between bee density and nut set. • Hand pollination confirms even with high bee density (i.e. close to hives), nut set can still be pollen limited. Just achieving a high density of bees is not enough to solve the pollen limitation problem. Some blocks, however, may have other limits to nut set that are not corrected by increased cross pollination. 2012/13 Proposal Although the absence of a simple and strong gradient effect might at first seem to be a “negative” result, there are some strong data here. It suggests trying to improve yield by increasing the number of hives is a limited strategy. And it seems that too many bees can even cause negative effects on nut set for nearby trees. Ultimately, the best way to improve pollination would be to increase the rate of cross pollination – in which case we would get more crop from fewer bees. Unfortunately there are no easy solutions for this, but we will examine some methods that might alter bee foraging behaviour such as en-pollination via felts, traps and flower bouquets to bring cross-pollen closer to receptive flowers. Meanwhile, it is important we understand what the right number of bees is (not too many, not too few) and how the arrangement of hives can effect bee density across the orchard, and possibly even influence the rate of cross pollination. In the second season (2012/13) we will survey points across larger areas of orchards where, for logistical and access limitations, some trees are a relatively long distance from hives. We will focus particularly on nut counts and hand pollinations as tools to help understand which parts of an orchard appear to be getting less cross pollination and whether this correlates to hive drops and locations (in particular, larger drops further apart).
Introduction We know that pollination by bees is
essential for a good almond crop. In fact almond growers are the biggest customers for paid pollination services in Australia. But how many bees do you need? In a perfect world you would order just enough bees, so that the crop is maximised, and the cost of getting the bees is minimised. Getting this right will also become particularly critical if Australia experiences any bee shortages, such as expected if the Varroa mite (a bee parasite) establishes itself. CSIRO and Australian Beekeeping Services are working together to answer the question “how many bees do you need?” This three year project commenced in July 2011. This project will use in-orchard observations and experiments to examine the efficiency of almond pollination by bees, focusing on a few different components: 1. What is the relationship between hive density and bee density for trees at different distances from hives? 2. What density and arrangement of hives is most likely to produce the best bee density for pollination? 3. Is there evidence (from pollination experiments) that suggests hive manipulations (such as pollen stripping, sugar feeding or en-pollination devices) are likely to improve pollination efficiency? 2011/12 Results As intended in the original experimental design, we created distance-from-hive effects in bee density and we also saw evidence of a relationship between low bee density and nut set. However, these patterns were only found in some blocks and were often statistically weak effects (even though significant) -- I think the more important lessons from the experiment come from some of the other observations. For example: • Bees strongly favoured moving within the rows where hives were placed, until late in the day when pollen and nectar ran low. • High bee density was in many instances associated with poor fruit set. This at least tells us the link between bee density and fruit set is very weak, and indicates flooding orchards with many bees is not an effective strategy to increase nut set.