Morpho-histological characterization of immature of the bioindicator midge Chironomus sancticaroli Strixino and Strixino (Diptera, Chironomidae)

ABSTRACTChironomidae immature are used as bioindicators of sediment quality in aquatic ecosystems and ecotoxicological assays. Histological descriptions for this family are outdated and limited and there are no studies with Neotropical species. The aim of this study was to describe the tissue architecture of several organs of the larva of Chironomus sancticaroli. For the description of the histological pattern, the larvae were fixed in Duboscq solution for insects at 56 °C, followed by routine histologic processing, infiltration in paraffin, and the sections were stained with Hematoxylin–Eosin. After examining the slides, the tube digestive, salivary gland, excretory, nervous, endocrine, circulatory, and integumentary systems and fat body were histologically characterized. The histology allows evaluation of cell morphology, and for being not expensive and easily accessible can be routinely used in biomonitoring. In addition, is a useful tool in ecotoxicological assays and allow to evaluate biomarkers at tissue and cell levels.

Low malathion concentrations influence metabolism in Chironomus sancticaroli (Diptera, Chironomidae) in acute and chronic toxicity tests

Low malathion concentrations influence metabolism in Chironomus sancticaroli (Diptera, Chironomidae) in acute and chronic toxicity tests. Organophosphate compounds are used in agro-systems, and in programs to control pathogen vectors. Because they are continuously applied, organophosphates often reach water sources and may have an impact on aquatic life. The effects of acute and chronic exposure to the organophosphate insecticide malathion on the midge Chironomus sancticaroli are evaluated. To that end, three biochemical biomarkers, acetylcholinesterase (AChE), alpha (EST-α) and beta (EST-β) esterase were used. Acute bioassays with five concentrations of malathion, and chronic bioassays with two concentrations of malathion were carried out. In the acute exposure test, AChE, EST-α and EST-β activities declined by 66, 40 and 37%, respectively, at 0.251 µg L-1 and more than 80% at 1.37, 1.96 and 2.51 µg L-1. In chronic exposure tests, AChE and EST-α activities declined by 28 and 15% at 0.251 µg L-1. Results of the present study show that low concentrations of malathion can influence larval metabolism, indicating high toxicity for Chironomus sancticaroli and environmental risk associated with the use of organophosphates.