Production of key nutritional resources for domesticated honeybees

Thesis

Domesticated honeybees provide critical crop pollination services through their foraging activity. However, climate change and agricultural intensification increasingly lead beekeepers to rely on pollen substitute feeds, to support brood production and colony health. Commercial pollen substitutes provide protein and sugars but lack crucial sterols. Because insects cannot biosynthesise sterols, they require an exogenous, dietary source of sterols for reproduction and growth. Honeybees obtain vital sterols from floral pollen. By analysing the sterol profile of diverse tissues from honeybee colonies, I identified six key sterols that occur in consistent ratios and are likely to be essential. However, these complex molecules are present at low abundance in biological material and are challenging to synthesise chemically. This limits their commercial availability and represents a significant challenge for developing nutritionally complete bee feeds.

The main aim of this thesis was to genetically engineer yeast strains to sustainably produce rare pollen sterols that are needed by bees. Firstly, I engineered the oleaginous yeast Yarrowia lipolytica to produce a mixture of the key honeybee sterols. I incorporated the sterol-producing yeast into diets that were otherwise nutritionally complete and evaluated the effects of sterol supplementation on honeybee brood-rearing capabilities in a semi-field feeding trial. Colonies supplemented with yeast diets containing all six key sterols could rear brood for significantly longer than those fed diets without suitable sterols.

Next, I engineered a series of yeast strains to produce isotopically labelled sterols that I used to examine the sterol biology of commercial bumblebees. The results demonstrate that bumblebees use the same set of sterols as honeybees but can use these sterols more flexibly. Bumblebees, like honeybees, use dietary sterols directly and do not convert them to cholesterol, which is unusual among insect herbivores.

Finally, I consider the broader potential for using engineered microbes to create nutritionally complete feeds for other farmed insects. This thesis establishes a biotechnological method for producing rare sterols that is appropriate for supplementing commercial insect feeds.

Authors: Moore, E

• DOI: 10.5287/ora-pp6yybzm5
• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford
• Language: English
• Keywords: metabolic engineering; yeast; sterol; honeybee; bee; yarrowia
• Subjects: Insects; Biotechnology; Nutrition