SUBLETHAL PARAMETERS IN MORPHOLOGICALLY DEFORMED CHIRONOMUS LARVAE - CLUES TO UNDERSTANDING THEIR BIOINDICATOR VALUE

1. Parameters of condition between normal and deformed fourth instar l arvae of Chironomus gr. thummi (Kieffer, 1911) were compared in four p opulations: one reference (PE) and two metal-polluted sites (NP and SC H) in the River Dommel, and one site polluted by domestic sewage and c opper in the River Ijse (NEI). 2. The site PE ranked lowest for metal body burdens, deformities, mortalities and emergence duration, while S CH and NEI ranked highest. 3. Deformed and non-deformed larvae most of ten did not differ in length and weight (in situ end-points for growth ); when differences occurred, deformed larvae tended to be smaller. 4. The energy content and dry weights in one population (NEI) were lower in normal larvae than in the weakly deformed ones. The percentage of ash-free dry weight was lower in deformed larvae of the polluted Domme l sites, compared to the normal ones. 5. The in vitro emergence rate ( end-point for development of fourth instars) for the reference populat ion PE, both in its own sediment and in artificial cellulose substrate , was better than for the other sites. In two populations (NEI, SCH) t he development of deformed larvae in their own sediment was slower, wi th higher mortality, than for the normal larvae. In one population (NP ), normal and deformed larvae survived and developed equally well. The emergence rates of the respective populations were similarly ranked w hen the larvae were raised in an artificial cellulose substrate. 6. El ution peaks of alleged metal-binding proteins were lower in deformed l arvae from SCH and NEI, but higher in deformed larvae from NP, than in normal larvae. 7. A different development rate and mortality of defor med larvae in non-adapted populations and the possibility of metal ada ptation, as in site NP, may modulate the final outcome of deformity fr equencies, thus having an impact on the biomarker value of deformities in benthic midge larvae.