The energetic and survival costs of Varroa parasitism in honeybees

Abstract

The ectoparasite V. destructor is one of the major threats to Western honeybees’ production (A. mellifera) worldwide, causing colony losses and reducing bees’ productivity and pollinating capacity. Since parasitism produces high energy consumption in hosts, the aim of this study was to compare the effects of this ectoparasite on energy expenditure and survival rate in honeybees. Newborn bees were kept in chambers at 32 °C and 55% humidity with food ad libitum. Individual bees were taken at random and grouped into three treatments: T0 (no mites), T1 (one mite), and T2 (two mites). After the mites had fed on the bees, the metabolic rate (CO2 production = VCO2) was individually measured at 32 °C for 3 h. We also measured survival rate, using the same groups for 8 days. A significant effect of the number of mites on VCO2 was found (T0 = 3.14 μLCO2 min−1, T1 = 4.03 μLCO2 min−1 and T2 = 6.44 μLCO2 min−1, F(2) = 25.81, p < 0.001). The treatments did not affect significantly the bees’ survival (p = 0.283), despite the survival rates recorded were 57.5% in T0, 42.5% in T1, and 40.0% in T2. V. destructor clearly increases the energetic cost of living in bees and provoking a reduction of the survival rate even when this value was not significant statistically.