Ectoparasites and host energetics: house martin bugs and house martin nestlings

We measured the energy cost of ectoparasitism in an experimental study of the house martin bug Oeciacus hirundinis and its main host, nestlings of the house martin Delichon urbica. Nests were randomly assigned to inoculation with 0 (control) 10, or 100 bugs during egg laying, and this resulted in statistically significant differences in parasite loads following fledging of nestlings. Parasite loads negatively affected house martin nestlings as estimated from their body mass at age 16 days and from mass loss estimated over 1 day late in the nestling period. Daily energy expenditure (KJ/d), average daily metabolic rate (ml CO₂/g h), and mass independent daily energy expenditure (kJ/mass^0.67d) did not differ significantly between experimental treatments. However, average daily metabolic rate increased with increasing intensities of ectoparasitism. Mass independent daily energy expenditure also increased with higher levels of parasite infestation. These results demonstrate that the bug imposes an energy cost on its host by elevating the level of metabolism.