22.214.171.124. Type of food
Because diet can affect honey bee longevity (Schmidt et al., 1987), immune response to Nosema infection (Alaux et al., 2010b), as well as spore development (Porrini et al., 2011), it is important to carefully consider food provided to experimental bees. Generally, researchers should attempt to maintain their honey bees as healthy as possible.
Honey bees are capable of surviving for long periods of time on 50 % (weight / volume) sucrose solution (Barker and Lehner, 1978); however, to ensure normal development of internal organs and glands (Pernal and Currie, 2000), as well as proper immune response (Alaux et al., 2010b), supplementing a strict carbohydrate diet with protein, and even nutrients such as vitamins and minerals, is recommended for maintaining honey bees in the laboratory. Bee-collected pollen provides an adequate medium for providing protein and nutrients (Brodschneider and Crailsheim, 2010); however, such material may be contaminated with Nosema spores (Higes et al., 2008b) or pesticides (Pettis et al., 2012). Additionally, it is possible that pollen may stimulate N. ceranae development by promoting bee health (Porrini et al., 2011).
Therefore, in addition to ad libitum 50 % (weight / volume) sucrose solution (i.e. 100 g table sugar dissolved in 100 ml distilled water), individuals should be provided with an easily accessible source of multi-floral, radiation sterilised, bee-collected pollen ad libitum as described by Williams et al. (2013) and Human et al. (2013) in the BEEBOOK.
Further studies are needed to investigate the effects of commercial pollen substitutes on Nosema development and individual bee health before they should be considered as a replacement for bee collected pollen.
To sterilize for N. apis spores, pollen can be exposed to ≥0.2x106 rads gamma radiation from cobalt-60 (Katznelson and Robb, 1962) or heat treated at 49°C for 24 hours (Cantwell and Shimanuki, 1969). On the other hand, very little is known about the factors responsible for making N. ceranae spores non-viable in bee products. N. ceranae will lose viability during freezing (Forsgren and Fries, 2010), but it is more resistant to heat than its congener (Fenoy et al., 2009). It is likely that temperatures and / or exposures higher than required for N. apis spore destruction will also render N. ceranae spores non-viable. As a result, a combination of heating and freezing pollen may be possible to develop as an alternative to radiation for sterilising bee-collected pollen of Nosema spores. Specific protocols need to be developed for this purpose because to date we only know that one week of freezing kills approximately 80 % of N. ceranae spores (Fries, 2010), and we do not know what temperatures will reduce the nutritive value of pollen.