Seed coating (‘seed treatment’) is the leading delivery method of neonicotinoid insecticides in major crops such as soybean, wheat, cotton and maize. However, this prophylactic use of neonicotinoids is widely discussed from the standpoint of environmental costs. Growing soybean plants from neonicotinoid-coated seeds in field, we demonstrate that soybean aphids (Aphis glycines) survived the treatment, and excreted honeydew containing neonicotinoids. Biochemical analyses demonstrated that honeydew excreted by the soybean aphid contained substantial concentrations of neonicotinoids even one month after sowing of the crop. Consuming this honeydew reduced the longevity of two biological control agents of the soybean aphid, the predatory midge Aphidoletes aphidimyza and the parasitic wasp Aphelinus certus. These results have important environmental and economic implications because honeydew is the main carbohydrate source for many beneficial insects in agricultural landscapes.

Neonicotinoid insecticides have posed a great threat to non-target organisms, yet the mechanisms underlying their toxicity are not well characterized. Major modes of action (MoAs) of imidacloprid were analyzed in an aquatic insect Chironomus dilutus. Lethal and sublethal outcomes were assessed in the midges after 96-h exposure to imidacloprid. Global transcriptomic profiles were determined using de novo RNA-sequencing to more holistically identify toxicity pathways. Transcriptional 10% biological potency values derived from ranked KEGG pathways and GO terms were 0.02 (0.01–0.08) (mean (95% confidence interval) and 0.05 (0.04–0.06) μg L⁻¹, respectively, which were more sensitive than those from phenotypic traits (10% lethal concentration: 0.44 (0.23–0.79) μg L⁻¹; 10% burrowing behavior concentration: 0.30 (0.22–0.43) μg L⁻¹). Major MoAs of imidacloprid in aquatic species were identified as follows: the activation of nicotinic acetylcholine receptors (nAChRs) induced by imidacloprid impaired organisms’ nerve system through calcium ion homeostasis imbalance and mitochondrial dysfunction, which posed oxidative stress and DNA damage and eventually caused death of organisms. The current investigation highlighted that imidacloprid affected C. dilutus at environmentally relevant concentrations, and elucidated toxicity pathways derived from gene alteration to individual outcomes, calling for more attention to toxicity of neonicotinoids to aquatic organisms.

The life cycle parameters of the benthic invertebrate Chironomus riparius make it a relevant organism for use in multi-generation chronic ecotoxicology tests. Since studies on chronic exposures with fullerene carbon nanoparticles have revealed adverse effects at lower concentration ranges, it is crucial to gain understanding of the consequences in following generations. The aims of this study were to investigate whether sediment-associated fullereneC60 impacts on C. riparius emergence and breeding, thus affecting the growth of the second generation. Larvae were exposed to fullerene-spiked sediment at concentrations of 0.5, 10 and 40 mg/kg sediment dw. Total emergence and breeding success were monitored after the first generation and the newly hatched larvae from the first generation exposure were transferred either to continuous exposure or to pristine sediments without fullerene. Findings indicate that the presence of fullerenes have major impacts on the first generation, mainly shown as delayed emergence time of females. Increased larval growth was observed in the second generation, and we conclude that the C. riparius response to fullerene exposure indicated significant signs of recovery in second-generation larval growth. The result shows the effects to be important for population dynamics, revealing delayed female emergence time, which leads to situation where adults’ breeding is inhibited.

Pyrethroids and metals were simultaneously detected in aquatic environment and showed antagonistic lethality to the benthic invertebrate, Chironomus dilutus. Accelerated biotransformation of pyrethroids in organism by the presence of metals was proposed as the likely reason for the antagonism. Mechanistic explanation for the role of toxicokinetics of pyrethroids in the antagonistic interaction would help better understanding the reasons for the joint toxicity. The goal was achieved in the current study by evaluating the impact of cadmium on toxicokinetic parameters of permethrin in C. dilutus, and by explaining the interaction through quantifying the activity and gene expression of biotransformation-related enzymes. Toxicokinetic parameters were simulated using a first-order kinetic model. Bioconcentration factors and uptake and elimination rate constants for permethrin were not significantly changed with the addition of cadmium at sublethal level, neither did the activity of enzymes, including glutathione S-transferase (GST), carboxylesterase (CarE), catalase and lipid peroxidation. Yet, the activities of metabolism-related enzymes (GST and CarE) showed an elevating tendency with adding cadmium. Furthermore, the expression of metabolism-related genes, including cytochrome P450 and glutathione S-transferase genes were significantly up-regulated in C. dilutus exposed to a mixture of permethrin and cadmium compared with permethrin only. Although co-exposure to cadmium did not induce toxicokinetic changes of permethrin in C. dilutus, it did enhance the activity of metabolic enzymes which were encoded by the metabolism-related genes, suggesting an acceleration of biotransformation of permethrin to less toxic metabolites in the midges. This possibly explained the antagonistic interaction for permethrin and cadmium.

The distribution and speciation of arsenic (As) were analyzed in individuals of various life stages of a midge, Chironomus riparius, and the mosquito Culex tarsalis exposed to 1000 μg/l arsenate. X-ray absorption spectroscopy (XAS) revealed that C. riparius larvae accumulate As in their midgut, with inorganic arsenate [As(V)] being the predominant form, followed by arsenite [As(III)] and an As-thiol. Reduced concentrations of As in pupal and adult stages of C. riparius indicate excretion of As between the larval and pupal stages. In adults, As was limited to the thorax, and the predominant form was an As-thiol. In Cx. tarsalis, As was not found in high enough concentrations to determine As speciation, but the element was distributed throughout the larva. In adults, As was concentrated in the thorax and eyes of adults. These results have implications for understanding the biotransformation of As and its movement from aquatic to terrestrial environments.

The effect of microplastics (MP) exposure on the chironomid species Chironomus riparius Meigen, 1804 was investigated using the OECD sediment and water toxicity test. Chironomid larvae were exposed to an environmentally relevant low microplastics concentration (LC), a high microplastics concentration (HC) and a control (C). The LC was 0.007 g m⁻² on the water surface + 2 g m⁻³ in the water column + 8 g m⁻² in the sediment, and the HC was 10 X higher than this for each exposure. The size of the majority of the manufactured microplastic pellets varied between 20 and 100 μm. The MP mixture consisted of: polyethylene-terephtalate (PET), polystyrene (PS), polyvinyl-chloride (PVC) and polyamide (PA) in a ratio of 45%: 15%: 20%: 20%, respectively, for the sediment exposure; 100% polyethylene for the water column exposure; and 50% polyethylene: 50% polypropylene for the water surface exposure. Different endpoints were monitored, including morphological changes in the mandibles and mentums of 4th instar larvae, morphological changes in the wings, mortality, emergence ratio, and developmental time. A geometric morphometric analysis showed a tendency toward widening of the wings, elongation of the mentums and changing the shape of the mandibles in specimens exposed to both concentrations of microplastics. The development time of C. riparius was significantly prolonged by the MP treatment: 13.8 ± 0.5; 14.4 ± 0.6; and 15.3 ± 0.4 days (mean ± SD) in the C, LC, and HC, respectively. This study indicates that even environmentally relevant concentrations of MP mixture have a negative influence on C. riparius, especially at the larval stage.

The possible toxicity of nanoparticles (NPs) to aquatic organisms needs to be investigated for chronic effects at low concentrations. Chronic effects of carbon NPs, fullerenesC60, on the midges of Chironomus riparius at different life stages on larvae and adult midges were investigated. Sediment associated fullerenesC60 were studied by 10-day growth and 42-day emergence tests with artificial sediment at nominal concentration ranges 0.0004–80 mg/kg dry weight. The body length decreased in the lower tested concentrations (0.0025–20 mg/kg), but the effect vanished with higher concentrations. Delayed emergence rate observed at 0.5 mg/kg. The observed effects correlated with analyzed sediment particle sizes indicating that small agglomerates of fullerene have more significant effects on C. riparius than larger agglomerates observed with higher C60 doses. The results reveal that fullerene may pose risks to benthic organisms, emerging as changes in the ecotoxic parameters studied here which inflects by the survival of the population.

Pyrethroid insecticides and metals commonly co-occurred in sediment and caused toxicity to benthic organisms jointly. To improve accuracy in assessing risk of the sediments contaminated by insecticides and metals, it is of great importance to understand interaction between the contaminants and reasons for the interaction. In the current study, permethrin and cadmium were chosen as representative contaminants to study joint toxicity of pyrethroids and metals to a benthic invertebrate Chironomus dilutus. A median effect/combination index-isobologram was applied to evaluate the interaction between sediment-bound permethrin and cadmium at three dose ratios. Antagonistic interaction was observed in the midges for all treatments. Comparatively, cadmium-dominated group (the ratio of toxicity contribution from permethrin and cadmium was 1:3) showed stronger antagonism than equitoxicity (1:1) and permethrin-dominated groups (3:1). The reasons for the observed antagonism were elucidated from two aspects, including bioavailability and enzymatic activity. The bioavailability of permethrin, expressed as the freely dissolved concentrations in sediment porewater and measured by solid phase microextraction, was not altered by the addition of cadmium, suggesting the change in permethrin bioavailability was not the reason for the antagonism. On the other hand, the activities of metabolic enzymes, glutathione S-transferase and carboxylesterase in the midges which were exposed to mixtures of permethrin and cadmium were significantly higher than those in the midges exposed to permethrin solely. Cadmium considerably enhanced the detoxifying processes of permethrin in the midges, which largely explained the observed antagonistic interaction between permethrin and cadmium.

Midge larvae (Chironomus riparius) were exposed to sediments from a deposition sampled at a site along the Rhône River (France) downstream of an industrial site releasing various perfluorinated chemicals. This sediment is characterized by high concentrations of perfluoroundecanoic acid (PFUnA) and perfluorotridecanoic acid (PFTrDA) and a low perfluorooctane sulfonate (PFOS) concentration. Concentrations of 23 perfluoroalkyl compounds, including C4–C14 carboxylate acids, C4–C10 sulfonates, and seven precursors, were analyzed in overlying and pore water, sediment, and larvae. Midge larvae accumulated carboxylate acids (C11–C14), PFOS, and two precursors (perfluorooctane sulfonamide: FOSA and 6:2 fluorotelomer sulfonic acid, 6:2 FTSA). These substances accumulated mainly during the fourth instar larvae exponential growth phase. Accumulation of 6:2 FTSA, PFUnA, and PFOS occured via trophic and tegumentary routes. Other compounds mainly accumulated from food. Kinetics followed a partition model, from which uptake and elimination constants were derived.

During acute exposure, polycyclic aromatic compounds (PACs) act mainly by narcosis, but during chronic exposure the same compounds may exert sublethal life cycle effects. The aim of this study was therefore to evaluate the chronic effects of sediment spiked PACs on the emergence of the midge Chironomus riparius. Three isomer pairs were selected, and 28-day LC50 values and 50% emergence times (EMt50) were determined. Concentration-response relationships were observed for phenanthrene, acridine, phenanthridine and acridone. Anthracene and phenanthridone had no effect on total emergence, but did cause a delay in emergence. Calculated porewater LC50 values correlated well with logKow values, suggesting narcosis as mode of action. In contrast, effect concentrations for delay in emergence (EMt50) deviated from narcosis, suggesting a specific mode of action during chronic exposure. It is concluded that emergence is a powerful endpoint to detect life cycle effects of PACs on a key sediment inhabiting invertebrate. Emergence of Chironomus riparius is a sensitive endpoint to detect life cycle effects of PACs.