The transmission of Epistylis daphniae infection among Boeckella triarticulata and the effect of peritrich epizoites on the copepod hosts were examined at 15 °C in the laboratory. After being paired with carrier copepodites, 97.5% of non-carrier adults became hosts to E. daphniae. When food was present there was no difference between carriers and non-carriers in growth of copepodites, and in survival and reproduction of adults. When food was absent, copepods infected with E. daphniae survived for shorter periods than non-carriers (p < 0.002). Therefore, colonial peritrichs may contribute to the decline of copepod populations when they are in a food-limited environment.