2.2.5. Determining dry weight

The dry weight of adult bees is determined by putting whole bees or their body parts (see section 2.2.4.) in individually labelled and pre-weighed Eppendorf tubes in an incubator at 55-70°C; 60°C can be recommended (Henderson, 1992). The tubes remain open during incubation. Dry weight is reached when the sample show constant weight in successive measures, which usually occurs within 7 days in honey bees, depending on incubation temperature. Samples can also be transferred to weighing dishes, but care must be taken not to lose extremities. Refer to the procedure described in section 2.2.3 to weigh the dried samples. The dry weight of newly emerged bees indicates the nutritional investment in larvae, which may result in different emerging weights during season. In adult bees, dry weight changes depending on nutrition and age, reaching a maximum after five days, and decreases again towards the foraging age (Hrassnigg and Crailsheim, 2005). Finally, parasites like the varroa mite can exert weight differences of more than 10% in emerging honey bee drones (Duay et al., 2003).