Influence of the population density and the amount of food on Chironomus plumosus [L.] and Tubificidae. Laboratory experiments

The aim of this paper has been to examine experimentally the importance of the density of larvae and of the addition of the food for Chironomus and Tubificidae using selected parameters and indices of their populations. Increase of the density of Chironomus plumo- sus larvae (0.5–50.0 thousands ind. m⁻²) in laboratory experiments resulted in the decrease of emergence of imagos, number of tube apertures (3.5–0.4 apertures ind.⁻¹), and in the lower rate of tubes building. The addition of the food (powdered dry daphnids or food tablets for aquarial fish) had only slight effect on tube numbers but it decreased clearly the getting out of larvae from tubes (probably due to improved feeding conditions inside tubes). It had also a slight negative effect on the survival of larvae. Numbers and individual growth of Tubificidae were positively dependent on the addition of the food (also in the form of naturally dead Chironomus larvae) and negatively – on the density of Chironomus.