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NEW ZEALAND BEEKEEPER, MARCH 2017
TREES FOR BEES CORNER
MANUKA MYSTERIES: THE BIOLOGY OF A FLOWER
Linda Newstrom-Lloyd (Trees for Bees Botanist)
The fascinating flowers of the mānuka tree (Leptospermum scoparium) have proven to be somewhat mysterious, with many conflicting accounts of how the flower works and what it provides.
2. Does pollen reliably get into the honey? We have regularly observed mānuka pollen on the surface of nectar discs. Pollen falls into the nectar in four different ways: by gravity, by mechanical shaking of the flower, by falling off native bees’ pollen loads on their legs, and by brushing off anthers due to the movements of the honey bees taking nectar. We would, therefore, expect mānuka pollen to be carried in the honey, especially if bees are working in the flower. The next question is how much pollen is typical, both for the relative percentage pollen count and the absolute pollen count (APC) per gram (Petersen & Bryant, 2011). Further research is needed on this aspect. 3. Do bisexual flowers produce more nectar than male flowers? We observed mānuka nectar production over the life of 30 flowers for seven days at Rangitukia. At this site, we were surprised to see male flowers producing as much nectar as bisexual flowers, but we will need more data to test this statistically. Some researchers say that male flowers produce less nectar and this may be true in some varieties, as this is one of the floral strategies that plants use to improve their pollination outcomes. Further studies are needed. 4. Would it be easy to collect pollen to add to honey? We have extracted pollen by direct manual methods from many types of flowers. Small flowers with small anthers (such as mānuka) are very difficult, whereas large anthers (such as in New Zealand flax or tulip trees), or large flowers with hundreds of large anthers (such as in kiwifruit, camellia, and peonies) are very easy. So we think that it would not be easy to collect pure pollen directly from mānuka flowers. Certainly the process would be unlikely to be cost effective. 5. What methods are best for collecting nectar? Nectar collection for analysis of activity and sugars can be performed in several ways. Dr Megan Grainger has published an excellent account of different sampling techniques in The New Zealand BeeKeeper (Grainger, 2016) and many research projects are focused on nectar; for example, by Dr Michael Clearwater and Stevie Noe at the University of Waikato. From our results on the flower’s life cycle, we would suggest that leaving the fine-mesh bag on the branch for longer than the customary 24 hours (say, three to five days) would allow more nectar to accumulate in the flower and make it easier to collect the samples. This practice would, of course, have to be modified for rainy days (that would dilute the nectar) and very hot, sunny days (that would evaporate the nectar, making it too viscous to collect). It will depend on the weather patterns and the variety of mānuka that you are working with.
For example, we have heard and read about ideas such as:
• honey bees do not collect mānuka pollen
• mānuka honey does not have mānuka pollen in it (or at least it is not a reliable predictor of mānuka honey)
• bisexual flowers produce more nectar than male flowers
• adulteration of honey with mānuka pollen would be easy.
In addition, many people ask about how to get enough nectar to test for activity.
Trees for Bees investigates The main goal of Trees for Bees is to provide planting lists of superior bee plants that will produce plentiful pollen and abundant nectar to nourish honey bees. To that end, we continually investigate the flowering times, the morphology and biology of the flowers, and the access for bees to the pollen and nectar rewards. Drawing on our past research from throughout New Zealand over the past 10 years, as well as new detailed observations, we have compiled the photo essay on the next few pages to illustrate the life of the mānuka flower and clear up some of the misconceptions about mānuka pollen and nectar. Key points from our investigations 1. Do honey bees collect mānuka pollen? Based on our field observations of insects in the flowers at several sites, we have not seen honey bees actively packing mānuka pollen into their baskets. However, the pollen does get brushed onto their bodies, and we have seen photos of bees with small partial pollen loads in mānuka flowers, but the identity of the pollen has not been confirmed. A number of reasons might explain this. The small anthers face inward and have extremely small pollen grains, so it may not be cost effective for honey bees if better pollen is easier to access on other plant species. The pollen may have a deterrent (e.g., scent), but this has not been investigated. Native bees have a different system of collecting pollen, so they harvest and pack mānuka pollen rapidly and efficiently as we have observed in our studies. Some beekeepers say that honey bees sometimes collect the pollen but some other beekeepers say they have not seen it; therefore further data are needed to draw a conclusion.
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