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1 Polish Journal of Ecology

1 2001

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Effects of the density of larvae and type of substrate on Chironomus plumosus L. (Diptera: Chironomidae) population. Laboratory experiments

Kajak Z., Prus P.

Polish Journal of Ecology

2001

Vol. 49, nr 4

369-378

Strong dependence of larval tube numbers on the population density, the condition of larvae and feeding situation occurred, but no correlation with the type of substrate was found. Numbers of larval tubes per individual were on the average 2.6 times lower at high (20 and 40 thousands ind. m^-2) than at low (2 - 2.5 thousands ind. m^-2) initial densities of larvae. They fluctuated strongly, but only at low densities, indicating the very high activity of larvae; high densities probably restrained this activity. The grown up larvae succeeded in finishingtheir full development in the mineral substrate with the tiny (<0.1 mm) layer of the natural mud at the top of it. No conical nettings (inside larval tubes) for food filtration were observed. The larvae fed mostly on the internal walls of their tubes; sometimes they also collected particles from the surface of the substrate (especially of substrates poor in the organic matter), after the food was furnished. The emergence of imagines depended on the larval density but quite differently than the numbers of tubes. The threshold for the decreased tube numbers per individual was between 2.5 and 20 thousands individuals m^2, while that for the emergence of imagines - between 20 and 40 thousands individuals m^2.