Figure 4.

The relationship between sucrose concentration and foraging efficiency. (a) Data (circles: drinking, and crosses: offloading) and fitted models (lines) of volumetric flow rate versus viscosity for drinking and offloading of sucrose solutions. The slope for drinking, −0.180 [95% CI: −0.211, −0.148], was less steep than that for offloading, −0.502 [−0.590, −0.413]. (b) Modelled relationships for relative instantaneous energy transfer versus concentration for drinking and offloading, using the fitted (slope) parameters from (a), and assuming an air temperature of 23°C for drinking, and abdominal temperature of 27°C for offloading. These relationships give optimum concentrations for maximizing energy transfer rates of 55% for drinking and 36% for offloading. (c) The mean (±95% CI) time spent transferring 35, 50 and 65% w/w sucrose solution. The ratio of time spent drinking to offloading is approximately 17 : 1, 11 : 1 and 6 : 1 for 35, 50 and 65% sucrose solution, respectively. n = 10 bees per concentration, each observation is the mean of 10 foraging bouts per bee. (Online version in colour.)