Environmentally Relevant Concentrations of the Insecticide Fipronil Modulated Molecular Response in Chironomus riparius.

Pesticides employed worldwide for crop protection easily reach aquatic systems, which act as the main reservoirs, and become a risk factor for aquatic fauna. Fipronil is a broad-spectrum insecticide acting on the insect nervous system; however, other effects and systems unrelated to this mechanism could be affected in non-target organisms. Thus, the present study aimed to assess the impact of fipronil on the suborganismal response (gene expression and enzymatic activity) of Chironomus riparius larvae as a model organism in ecotoxicology. To this end, short-term toxicity tests were carried out with fourth-instar larvae exposed to 0.001, 0.01, and 0.1 µg L-1 of fipronil for 24 and 96 h. Messenger RNA levels of 42 genes related to diverse metabolic pathways were analyzed by real-time polymerase chain reaction, complemented with catalase (CAT), glutathione S-transferase (GST), and acetylcholinesterase (AChE) activities. Few effects were observed at 24 h; however, after longer exposure (96 h), genes involved in the endocrine, detoxification, stress, and immune response pathways were altered. Moreover, fipronil at 96 h increased CAT and GST activity at 0.01 µg L-1 and AChE at the highest concentrations. The results demonstrate that even low environmentally relevant fipronil concentrations can modulate the molecular response of several cellular pathways in C. riparius after short-term exposure. These results bring new information about the underlying response of fipronil and its mode of action on a key aquatic invertebrate. Despite no effects on mortality, strong modulation at the suborganismal level emphasizes the advantage of biomarkers as early damage responses and the harmful impact of this pesticide on freshwater organisms. Environ Toxicol Chem 2024;43:405-417. © 2023 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Chironomus calligraphus Goeldi, 1905 (Diptera: Chironomidae) Larvae: Feeding Habits, Growth, and Maturation.

Chironomus calligraphus Goeldi, 1905 has a flexible life cycle with several generations per year, which can be modified by the quality and type of food. To categorize the functional feeding group of the species, food preference was evaluated in larval instars III and IV, through laboratory experiments and gut content analysis. To evaluate the influence of the type of food on the duration of the life cycle growth and maturation, experiments were carried out. Instar III preferred conditioned leaves and animal food, while instar IV preferred algae and fine particulate organic matter. Gut contents of instar IV collected from streams showed increased consumption of fine particulate organic matter than other items. All these observations allowed us to assign the species to the gatherer collector group. The duration of the life cycle varied between the different types of foods, being the conditioned leaves, animal food, and algae the items that caused a greater growth in the larvae and a faster passage to the pupal instar. Our results suggest that the opportunistic feeding behavior of C. calligraphus allows it to use several different foods, but the quality of the foods influences the length of the life cycle and this contributes to its plasticity.

Lethal and sublethal effects of the saline stressor sodium chloride on Chironomus xanthus and Girardia tigrina.

Salinization in freshwaters is gradually increasing as a result of human activities and climatic changes. Higher salt content causes stress for freshwater organisms. Sodium chloride (NaCl) is among the most frequently occurring salts in freshwater ecosystems. The objective of the present study was to investigate the lethal and sublethal effects of NaCl on freshwater ecosystems, using as test organism the dipteran Chironomus xanthus and the planarian Girardia tigrina. Acute tests showed that C. xanthus was more sensitive (48-h LC50 (median lethal concentration) of 2.97 g NaCl L-1) than G. tigrina (48-h LC50 of 7.77 g NaCl L-1). C. xanthus larvae growth rate (larvae length and head capsule width) was significantly reduced under exposure to concentrations as low as 0.19 g L-1 NaCl and higher. A delay in the emergence time (EmT50) was also demonstrated for the same concentration. Sublethal NaCl effects in G. tigrina included feeding inhibition (LOEC (lowest observed effect concentration) of 0.4 g L-1), reduced locomotion (LOEC = 0.2 g L-1), and 24-48-h blastema regeneration (LOEC = 0.2 g L-1 and 0.1 g L-1, respectively). The results demonstrated the toxicity of NaCl to C. xanthus and G. tigrina including sublethal effects that can result in negative consequences for populations in natural freshwaters under salinization.

Histological description of immature Chironomus columbiensis (Diptera: Chironomidae): A potential contribution to environmental monitoring.

Chironomids have been widely used in environmental monitoring and toxicity assays. Assessment criteria for chironomids range from the molecular-biochemical level to the population level. However, the use of markers to evaluate cellular and anatomical changes in organs and systems of individuals under contaminant exposure is still incipient. In this study, we conducted a histological description of the main systems and organs of immature Chironomus columbiensis. We used fourth instar larvae, obtained from a standardized culture, and confirmed this state through morphological and molecular methods. Larvae were fixed in Duboscq solution for insects during 48 hr, dehydrated in increasing dilutions of ethanol, and embedded and mounted in historesin to obtain 3 µm sections. The digestive, nervous, excretory, and integumentary systems and the fat body and testicles were analyzed through longitudinal and transversal sections, stained with hematoxylin-eosin (HE), and further photographed and described through light microscopy. This is the first description of internal morphology performed for C. columbiensis and can help in future histopathological analysis, because through bioaccumulation some of these organs are contaminant targets. It can even be a great taxonomic tool, since the characteristics of the histological pattern of C. columbiensis presented differences compared to other descriptions made in chironomids.

Lethal and sub-lethal effects of cyproconazole on freshwater organisms: a case study with Chironomus riparius and Dugesia tigrina.

The fungicide cyproconazole (CPZ) inhibits the biosynthesis of ergosterol, an essential sterol component in fungal cell membrane and can also affect non-target organisms by its inhibitory effects on P450 monooxygenases. The predicted environmental concentration of CPZ is up to 49.05 µg/L and 145.89 µg/kg in surface waters and sediments, respectively, and information about CPZ toxicity towards non-target aquatic organisms is still limited. This study aimed to address the lack of ecotoxicological data for CPZ, and thus, an evaluation of the lethal and sub-lethal effects of CPZ was performed using two freshwater invertebrates (the midge Chironomus riparius and the planarian Dugesia tigrina). The estimated CPZ 48 h LC50 (95% CI) was 17.46 mg/L for C. riparius and 47.38 mg/L for D. tigrina. The emergence time (EmT50) of C. riparius was delayed by CPZ exposure from 0.76 mg/L. On the other hand, planarians showed higher tolerance to CPZ exposure. Sub-lethal effects of CPZ on planarians included reductions in locomotion (1.8 mg/L), delayed photoreceptors regeneration (from 0.45 mg/L), and feeding inhibition (5.6 mg/L). Our results confirm the moderate toxicity of CPZ towards aquatic invertebrates but sub-lethal effects observed also suggest potential chronic effects of CPZ with consequences for population dynamics.

Tanytarsini (Diptera: Chironomidae) from madicolous habitat in Southeast Brazil: new species and new records.

Tanytarsini (Diptera: Chironomidae: Chironominae) collected from madicolous habitats in Brazil are analyzed, and three new species of Tanytarsus van der Wulp are described and illustrated: T. angelae sp. n. and T. alaidae sp. n. as adult male and T. alienus sp. n. as male and female. New records of another Brazilian Tanytarsus species are also presented, and immature stages of Paratanytarsus silentii Trivinho-Strixino are described.

Diversity and biomass of Chironomidae (Diptera) larvae in an impacted coastal lagoon in Rio de Janeiro, Brazil

Diversity and biomass of Chironomidae larvae were studied between January-November 1993 and March-November 1994 in an impacted lagoon in Rio de Janeiro, Southeastern Brazil, in an attempt to establish the ecological consequences of anthropogenic eutrophication processes. Nine hundred and seventy-five organisms belonging to the Tanypodinae, Orthocladiinae, and Chironominae were collected. Polypedilum (62%) and Chironomus (58%) were the most common genera found in the limnetic and littoral zones.

Foram estudadas a diversidade e a biomassa de larvas de Chironomidae entre janeiro e novembro de 1993 e março-novembro de 1994 em uma lagoa costeira no Estado do Rio de Janeiro, Sudeste do Brasil, com o objetivo de identificar as conseqüências ecológicas do processo de eutrofização artificial. Ao todo, 975 larvas de Tanypodinae, Orthocladiinae e Chironominae foram coletadas e Polypedilum (62%) e Chironomus (58%) foram os taxa mais comuns nas regiões litorânea e limnética.

Diversity and biomass of Chironomidae (Diptera) larvae in an impacted coastal lagoon in Rio de Janeiro, Brazil

Diversity and biomass of Chironomidae larvae were studied between January-November 1993 and March-November 1994 in an impacted lagoon in Rio de Janeiro, Southeastern Brazil, in an attempt to establish the ecological consequences of anthropogenic eutrophication processes. Nine hundred and seventy-five organisms belonging to the Tanypodinae, Orthocladiinae, and Chironominae were collected. Polypedilum (62%) and Chironomus (58%) were the most common genera found in the limnetic and littoral zones.

Foram estudadas a diversidade e a biomassa de larvas de Chironomidae entre janeiro e novembro de 1993 e março-novembro de 1994 em uma lagoa costeira no Estado do Rio de Janeiro, Sudeste do Brasil, com o objetivo de identificar as conseqüências ecológicas do processo de eutrofização artificial. Ao todo, 975 larvas de Tanypodinae, Orthocladiinae e Chironominae foram coletadas e Polypedilum (62%) e Chironomus (58%) foram os taxa mais comuns nas regiões litorânea e limnética.