4.10. Royal jelly

  • Check quality of royal jelly (preliminary experiments)
  • Store royal jelly in aliquots at -20°C until usage
  • Thaw royal jelly briefly before (à Section 5.4. Preparation and storage of diets)

Royal jelly is the brood food produced by nurse bees to specifically feed queen larvae. The immature queen is superabundantly fed, and older queen larvae are fed a different formation than worker larvae (Brouwers et al., 1987). This jelly is harvested by beekeeping operations and commercially available. Due to its manifold use, including for humans, much research on quality standards of this undefined hive product has been conducted. Royal jelly makes up a great part of the larvae’s laboratory diet; thus its quality strongly influences in vitro rearing success. The exact composition of royal jelly and the importance of several of its components for larval development are not clear. Fresh royal jelly contains roughly 9-18 % protein, 7-18 % sugars and 3-8 % lipids (Sabatini et al., 2009). The water content varies between 50 and 70 % (Rembold and Dietz, 1965; Sabatini et al., 2009; Zheng et al., 2011). Royal jelly contains 10-hydroxy-2-decenoic acid (10-HDA), an antibacterial substance that is analysed as a freshness parameter in routine testing.

The biochemical composition of royal jelly depends on harvesting season and regional origin (Sabatini et al., 2009). Moisture and protein content also depend on the harvesting day (i.e. first, second, third) after grafting of larvae (Zheng et al., 2011). The latter fact has long been demonstrated to influence the development of ovaries of in vitro-reared larvae (Mitsui et al., 1964). Accordingly, differences even from several batches of royal jelly may significantly alter the quality (e.g. protein content, see Fig. 1) of in vitro diets and influence rearing success or susceptibility against pathogens. The quality of royal jelly is presumably also altered by shipping and storage condition and duration. Differences in freeze-dried, frozen or fresh royal jelly (harvested during investigation year) can be expected. For experiments involving the testing of pathogens, the presence of unwanted antibiotics in royal jelly must be excluded, hence we recommend the use of organic royal jelly or own production. Royal jelly may also be irradiated at 20 kGy for purposes of sterilization. Though it is not known if this will impact its structural integrity or affect its developmental impact on larvae, Gregorc and Ellis (2011) and Gregorc et al. (2012) reared larvae successfully on irradiated royal jelly. It is advisable to test every new batch of royal jelly to make sure that the results obtained with the ‘old’ batch can be reproduced with the ‘new’ batch. Sometimes it might be necessary to test several batches before a batch suitable to replace the consumed charge can be identified.

Fig. 1. Comparison of: a. protein and; b. sugar content of brood food of young (1-3 d) and old (4-6 d) worker larvae (Data summarized from Kunert and Crailsheim, 1987) and laboratory diet, both percentages of dry weight. Protein decrease and sugar increase are due to the increase in sugar added to diets (Aupinel et al., 2005). Range of content is determined by variation in royal jelly protein (Sabatini et al., 2009) and sugar (Brouwers, 1984) content. Protein and sugar in yeast were excluded from calculations.

Figure 1