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NEW ZEALAND BEEKEEPER, MAY 2017
WHAT WE HAVE LEARNED ABOUT GIANT WILLOW APHID HONEYDEW HONEY RESEARCH Steve Howse, Analytica Laboratories The giant willow aphid arrived in New Zealand in the last five to 10 years, and produces a honeydew collected by bees which they turn into honey. This honey often contains crystals of the complex sugar melezitose, which makes it hard to extract using conventional techniques, and is less useful for bees to use as a source of food for the hive. Using an alternative extraction technique, there is potential for it to be a unique honey that rivals European forest honeys.
The giant willow aphid (GWA) is an unwelcome import to New Zealand that appears to be here to stay. Articles in The New Zealand BeeKeeper since 2015, often by or involving Dr John McLean from Gisborne, have described the impact that the GWA is having on hives (McLean, 2015; Foster, 2016, 2017). Judging by the buzz of activity in the willows growing on our property in the central Waikato, this season will be no different! At Analytica we have been involved in testing honey that has been made by bees collecting GWA honeydew. While we have not carried out any large-scale studies on this matter, we thought it would be useful to share some observations about what we have seen, and heard. By sharing, we hope we can contribute to the industry’s learning to best manage the impact of this insect pest. As with other articles on this subject, I again acknowledge the valuable input provided when writing this by Dr John McLean. We are fortunate to have the benefit of John’s enthusiasm and enquiring mind at work for the benefit of our industry in New Zealand. John did a presentation on the topic at the 2016 Apiculture Conference on Tuesday, 21 June 2016, which can be accessed via https:// apinz.org.nz/news/conference-videos/ Figure 1. Colony of giant willow aphids with several winged adults collected March 23, 2015. Photo: Dr John McLean.
Figure 2. A honey bee and bumble bee feeding on honey dew from the giant willow aphid at Te Rahu nursery. Photo: Steve Pawson, SCION Research.
Giant willow aphids produce honeydew by feeding on willow trees The giant willow aphid (Tuberolachnus salignus) is an insect that lives by sucking the sap from willow (and poplar) trees. In the same way that a mosquito sucks blood from a person, or a passion vine hopper sucks sap from a tutu plant, the aphids effectively insert a feeding tube into the stem of the willow tree and start gulping up the sugary sap flowing in there. Plants naturally have sugars in their sap (along with amino acids and other things useful for plant growth). In the case of willows, some old research (Mittler, 1958) states that the sap contains sugar in the form of sucrose. In the process of digesting the sap, the aphids use some of the sugar for their own growth, and convert some into a more complex sugar
called melezitose as a way of managing osmotic pressure in their digestive tract. The aphids excrete the digested sap as a sugary honeydew, which is very attractive for hungry bees and wasps (especially in late summer and autumn when other sources of feed are getting scarce). The melezitose is a key thing in this process— while simple sugars (glucose, fructose, and sucrose) are a good source of nutrition for bees, melezitose is, unfortunately, indigestible for them. Features of honey made from giant willow aphid honeydew Without going into a lot of detail, following are some observations that honey producers have made to us about honey made from GWA honeydew, or that we have observed ourselves at Analytica. Some of them need
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