Field-relevant Concentrations Research Articles

Higher temperatures exacerbate effects of antibiotics on methanogenesis in freshwater sediment

Methane (CH4) emissions from natural systems are rising in a concerning manner with an incomplete understanding of its drivers. Recently, chemical stressors such as antibiotics have been suggested as a thus far overlooked factor increasing methanogenesis in freshwaters. Since usage and toxicological impact of antibiotics could increase in a warming climate, we assessed the temperature-dependence of antibiotic effects on methanogenesis. In this light, we conducted anaerobic incubations with freshwater sediment at 10, 15, and 20 °C in presence of a mixture of five antibiotics at field-relevant concentrations. Weekly measurements of CH4 showed a strong temperature dependence of antibiotic effects by changing effect sizes, directions and dynamics. While antibiotics reduced CH4 production at 10 °C, methanogenesis was elevated at 15 °C with the most pronounced increase occurring at 20 °C. Furthermore, antibiotics changed the prokaryotic assemblage at all temperatures and effect patterns of CH4 producing Methanomicrobia strongly followed the patterns observed for methanogenesis. While analyses of compound-specific stable isotopes and the metatranscriptome suggest the acetoclastic pathway as most relevant, linking prokaryotic structure to function remains one of the most significant research challenges. Nevertheless, the evidence provided by this study suggests a positive relationship between temperature and the stimulating effects of antibiotics on CH4 production.

Uncovering hidden dangers: The combined toxicity of abamectin and lambda-cyhalothrin on honey bees

Studying the toxic effects of pesticides on bees has consistently been a prominent area of interest for researchers. Nonetheless, existing research has predominantly concentrated on individual toxicity assessments, leaving a gap in our understanding of mixed toxicity. This study delves into the individual and combined toxic effects of abamectin (ABA) and lambda-cyhalothrin (LCY) on honey bees (Apis mellifera) in laboratory settings. We discovered that ABA (96 h-LC50 value of 0.079 mg/L) exhibited greater acute toxicity to honey bees compared to LCY (96 h-LC50 value of 9.177 mg/L). Moreover, the mixture of ABA and LCY presented an acute antagonistic effect on honey bees. Additionally, our results indicated that exposure to LCY, at medium concentration, led to a reduction in the abundance of gut core bacterium Snodgrassella. However, an increase in the abundance of Bifidobacterium was noted when exposed to a medium concentration of LCY and its mixture with ABA. Transcriptomic analysis revealed significant regulation of certain genes in the medium concentration of all three treatments compared to the control group, primarily enriching in metabolism and immune-related pathways. Following chronic exposure to field-relevant concentrations of ABA, LCY, and their mixture, there were significant alterations in the activities of immunity-related enzyme polyphenol oxidase (PPO) and detoxification enzymes glutathione S-transferase (GST) and carboxylesterase (CarE). Additionally, the expression of four genes (abaecin, cyp9e2, cyp302a1, and GstD1) associated with immune and detoxification metabolism was significantly altered. These findings suggest a potential health risk posed by the insecticides ABA and LCY to honey bees. Despite exhibiting acute antagonistic effect, mixed exposure still induced damage to bees at all levels. This study advances our knowledge of the potential adverse effects of individual or combined exposure to these two pesticides on non-target pollinators and offers crucial guidance for the use of insecticides in agricultural production.

Neonicotinoid exposure increases Varroa destructor (Mesostigmata: Varroidae) mite parasitism severity in honey bee colonies and is not mitigated by increased colony genetic diversity.

Agrochemical exposure is a major contributor to ecological declines worldwide, including the loss of crucial pollinator species. In addition to direct toxicity, field-relevant doses of pesticides can increase species' vulnerabilities to other stressors, including parasites. Experimental field demonstrations of potential interactive effects of pesticides and additional stressors are rare, as are tests of mechanisms via which pollinators tolerate pesticides. Here, we controlled honey bee colony exposure to field-relevant concentrations of 2 neonicotinoid insecticides (clothianidin and thiamethoxam) in pollen and simultaneously manipulated intracolony genetic heterogeneity. We showed that exposure increased rates of Varroa destructor (Anderson and Trueman) parasitism and that while increased genetic heterogeneity overall improved survivability, it did not reduce the negative effect size of neonicotinoid exposure. This study is, to our knowledge, the first experimental field demonstration of how neonicotinoid exposure can increase V. destructor populations in honey bees and also demonstrates that colony genetic diversity cannot mitigate the effects of neonicotinoid pesticides.

Adverse effects of crushed seafloor massive sulphide deposits on the boreal deep-sea sponge Geodia barretti Bowerbank, 1858 and its associated fauna

Abundant mineral resources in the deep sea are prospected for mining for the global metal market. Seafloor massive sulphide (SMS) deposits along the Mid-Atlantic Ridge are one of the potential sources for these metals. The extraction of SMS deposits will expose adjacent marine ecosystems to suspended particle plumes charged with elevated concentrations of heavy metals and other potentially toxic compounds. Up to date there is no information about the impact of mining activities on deep-sea benthic ecosystems such as abundant deep-sea sponge grounds in the North Atlantic Ocean. Sponge grounds play a major role in benthic-pelagic coupling and represent an important habitat for a diversity of vertebrates, invertebrates and microorganisms. To simulate the effects of mining plumes on benthic life in the deep sea, we exposed Geodia barretti, a dominant sponge species in the North Atlantic Ocean, and an associated brittle star species from the genus Ophiura spp. to a field-relevant concentration of 30 mg L−1 suspended particles of crushed SMS deposits. Three weeks of exposure to suspended particles of crushed SMS resulted in a tenfold higher rate of tissue necrosis in sponges. All brittle stars in the experiment perished within ten days of exposure. SMS particles were evidently accumulated in the sponge's mesohyl and concentrations of iron and copper were 10 times elevated in SMS exposed individuals. Oxygen consumption and clearance rates were significantly retarded after the exposure to SMS particles, hampering the physiological performance of G. barretti. These adverse effects of crushed SMS deposits on G. barretti and its associated brittle star species potentially cascade in disruptions of benthic-pelagic coupling processes in the deep sea. More elaborate studies are advisable to identify threshold levels, management concepts and mitigation measures to minimize the impact of deep-sea mining plumes on benthic life.

Performance of wood waste biochar and food waste compost in a pilot-scale sustainable drainage system for stormwater treatment

Sustainable drainage system (SuDS) for stormwater reclamation has the potential to alleviate the water scarcity and environmental pollution issues. Laboratory studies have demonstrated that the capacity of SuDS to treat stormwater can be improved by integrating biochar and compost in the filter media, whereas their performance in scaled-up applications is less reported. This study examines the effectiveness of a pilot-scale SuDS, bioswale followed by bioretention, amended with wood waste biochar (1, 2, and 4 wt.%) and food waste compost (2 and 4 wt.%) to simultaneously remove multiple pollutants including nutrients, heavy metals, and trace organics from the simulated stormwater. Our results confirmed that SuDS modified with both biochar (2 wt.%) and compost (2 wt.%) displayed superior water quality improvement. The system exhibited high removal efficiency (> 70%) for total phosphorus and major metal species including Ni, Pb, Cd, Cr, Cu, and Zn. Total suspended solids concentration was approaching the detection limit in the effluent, thereby confirming its capability to reduce turbidity and particle-associated pollutants from stormwater. Co-application of biochar and compost also moderately immobilized trace organic contaminants such as 2,4-dichlorophenoxyacetic acid, diuron, and atrazine at field-relevant concentrations. Moreover, the soil amendments amplified the activities of enzymes including β-D-cellobiosidase and urease, suggesting that the improved soil conditions and health of microbial communities could possibly increase phyto and bioremediation of contaminants accumulated in the filter media. Overall, our pilot-scale demonstration confirmed that the co-application of biochar and compost in SuDS can provide a variety of benefits for soil/plant health and water quality.

Acute toxicity and bioaccumulation of common urban metals in Bombus impatiens life stages

Metal contamination is ubiquitous in urban areas and represents a risk to arthropod species. Bees are exposed to metals while foraging within contaminated landscapes from multiple sources. Eliminating the risk of bee exposure to metals is complex, and requires an understanding of how bees become contaminated, how metals accumulate within bee bodies, and how this exposure influences their health. We selected Bombus impatiens, the common eastern bumble bee, as our focal species because it is the most frequently encountered bumble bee species in the eastern United States and common within urban greenspaces. The aims of this study were to quantify the lethal concentration exposure limit (LC50) for B. impatiens foragers, assess the bioaccumulation ability of environmentally relevant concentrations of common urban metals in adults, larvae, and pupae, and compare the LC50 values against field relevant concentrations collected by foraging bumble bees within a legacy city. Bumble bees were orally exposed to arsenic oxide, cadmium chloride, or chromium oxide in sucrose solution to encourage consumption. The LC50 for arsenic (As2O3 36.4 mg/L), cadmium (CdCl2 10.3 mg/L), and chromium (CrO3 189.6 mg/L) are 202×, 79×, and 1459× greater than concentrations found within urban bumble bee collected provisions, respectively. Adult bumble bees fed field realistic concentrations of metals accumulate significant amounts of cadmium and lead within their bodies, but do not accumulate chromium and arsenic. Additionally, adults accumulate significantly higher concentrations of metals than brood. While bumble bee foragers are unlikely to encounter lethal metal concentrations while foraging in contaminated landscapes, it is crucial to consider and understand how sublethal concentrations impact overall colony functioning. The results from this study highlight the need to identify hazards and bioaccumulation ability of common metals as bees respond differently to each metal species, as well as the impacts of metal mixtures on bioaccumulation and toxicity.

Mouthparts of the bumblebee (Bombus terrestris) exhibit poor acuity for the detection of pesticides in nectar.

Bees are important pollinators of agricultural crops, but their populations are at risk when pesticides are used. One of the largest risks bees face is poisoning of floral nectar and pollen by insecticides. Studies of bee detection of neonicotinoids have reported contradictory evidence about whether bees can taste these pesticides in sucrose solutions and hence avoid them. Here, we use an assay for the detection of food aversion combined with single-sensillum electrophysiology to test whether the mouthparts of the buff-tailed bumblebee (Bombus terrestris) detect the presence of pesticides in a solution that mimicked the nectar of oilseed rape (Brassica napus). Bees did not avoid consuming solutions containing concentrations of imidacloprid, thiamethoxam, clothianidin, or sulfoxaflor spanning six orders of magnitude, even when these solutions contained lethal doses. Only extremely high concentrations of the pesticides altered spiking in gustatory neurons through a slight reduction in firing rate or change in the rate of adaptation. These data provide strong evidence that bumblebees cannot detect or avoid field-relevant concentrations of pesticides using information from their mouthparts. As bees rarely contact floral nectar with other body parts, we predict that they are at high risk of unwittingly consuming pesticides in the nectar of pesticide-treated crops.

Mouthparts of the bumblebee (Bombus terrestris) exhibit poor acuity for the detection of pesticides in nectar

Bees are important pollinators of agricultural crops, but their populations are at risk when pesticides are used. One of the largest risks bees face is poisoning of floral nectar and pollen by insecticides. Studies of bee detection of neonicotinoids have reported contradictory evidence about whether bees can taste these pesticides in sucrose solutions and hence avoid them. Here, we use an assay for the detection of food aversion combined with single-sensillum electrophysiology to test whether the mouthparts of the buff-tailed bumblebee (Bombus terrestris) detect the presence of pesticides in a solution that mimicked the nectar of oilseed rape (Brassica napus). Bees did not avoid consuming solutions containing concentrations of imidacloprid, thiamethoxam, clothianidin, or sulfoxaflor spanning six orders of magnitude, even when these solutions contained lethal doses. Only extremely high concentrations of the pesticides altered spiking in gustatory neurons through a slight reduction in firing rate or change in the rate of adaptation. These data provide strong evidence that bumblebees cannot detect or avoid field-relevant concentrations of pesticides using information from their mouthparts. As bees rarely contact floral nectar with other body parts, we predict that they are at high risk of unwittingly consuming pesticides in the nectar of pesticide-treated crops.

Trisiloxane Surfactants Negatively Affect Reproductive Behaviors and Enhance Viral Replication in Honey Bees.

Trisiloxane surfactants are often applied in formulated adjuvant products to blooming crops, including almonds, exposing the managed honey bees (Apis mellifera) used for pollination of these crops and persisting in colony matrices, such as bee bread. Despite this, little is known regarding the effects of trisiloxane surfactants on important aspects of colony health, such as reproduction. In the present study, we use laboratory assays to examine how exposure to field-relevant concentrations of three trisiloxane surfactants found in commonly used adjuvant formulations affect queen oviposition rates, worker interactions with the queen, and worker susceptibility to endogenous viral pathogens. Trisiloxane surfactants were administered at 5 mg/kg in pollen supplement diet for 14 days. No effects on worker behavior or physiology could be detected, but our results demonstrate that hydroxy-capped trisiloxane surfactants can negatively affect queen oviposition and methyl-capped trisiloxane surfactants cause increased replication of Deformed Wing Virus in workers, suggesting that trisiloxane surfactant use while honey bees are foraging may negatively impact colony longevity and growth. Environ Toxicol Chem 2024;43:222-233. © 2023 SETAC. This article has been contributed to by U.S. Government employees and their work is in the public domain in the USA.

Assessing the toxicity of selected pesticides to Trichogramma ostriniae (Hymenoptera: Trichogrammatidae) pupae as a first step in the development of a potential novel deployment programme

ABSTRACT Trichogramma spp. have been used or have been proposed for use in biological control programmes of lepidopteran pests, including the European corn borer, Ostrinia nubilalis, the cotton bollworm, Helicoverpa armigera, and the spruce budworm, Choristoneura fumiferana. Releases are typically made by placing cards with parasitised eggs at set points in the field. However, this method can be cost-prohibitive due to its laborious nature. As a result, labour-saving mechanised release programmes have been developed, including distribution by spray equipment. However, few have investigated applying Trichogramma with a standard pesticide application (i.e. ‘tank mix’). As a first step to ascertain the feasibility of such a system, we observed the effect of immersion of T. ostriniae pupae in field-relevant concentrations of eight herbicides (bentazon, clethodim, fomesafen, quizalofop, Glacial acetic acid, glyphosate, imazamox, imazethapyr), three fungicides (Copper Hydroxide, flutriafol, and penthiopyrad), one insecticide (K+ salt of fatty acid), and five adjuvants (Ammonium Sulfate, Crop Oil Concentrate, Methylated seed oil, Non-ionic surfactant, and Urea-Ammonium Nitrate) on the emergence of T. ostriniae adults. The herbicides GAA and clethodim; the fungicides copper hydroxide, flutriafol, and penthiopyrad; and the adjuvants COC, MSO, and NIS all reduced T. ostriniae emergence compared to a water control. No emergence was observed with exposure to quizalofop, GAA, or K+ salt of fatty acid treatments. Other treatments did not affect emergence compared to water. Thus, deploying Trichogramma with a standard pesticide application may be a feasible labour-saving distribution method that warrants further investigation.

A mitotoxic fungicide alters post-ingestive glucose signals necessary for associative learning in honey bees

The Proboscis Extension Reflex (PER) paradigm trains honey bees to associate an odor with a sugar reward and is commonly used to assess impacts on associative learning after exposure to pesticides. While the effects of some types of pesticides have been well-investigated, relatively little attention has been focused on fungicides that are applied to flowering crops. We have previously shown that consumption of field-relevant concentrations of the fungicide Pristine® (active ingredients: 25.2% boscalid, 12.8% pyraclostrobin) impairs honey bee performance in an associative learning assay, but the mechanism of its action has not been investigated. We hypothesized that Pristine® interferes with carbohydrate absorption and/or regulation, thereby disrupting the post-ingestive feedback mechanisms necessary for robust learning. To test this hypothesis, we measured hemolymph glucose and trehalose levels at five time points during the ten minutes after bees consumed a sucrose solution. Pristine®-exposed bees had elevated baseline glucose concentrations in the hemolymph relative to control bees. Hemolymph glucose levels rose significantly within five minutes of feeding in control bees, but not in Pristine®-fed bees. These data suggest that the post-ingestive feedback mechanisms necessary for robust learning are disrupted in bees that have consumed this fungicide, providing a plausible mechanistic explanation for its effects on learning performance in the PER assay. Pristine®-exposed bees may have elevated hemolymph glucose levels because the fungicide elicits an inflammatory response. These results provide additional mechanistic understanding of the negative physiological effects of mitotoxic fungicides on this important pollinator.

Glyphosate affects larval gut microbiota and metamorphosis of honey bees with differences between rearing procedures

The honey bee Apis mellifera is a sentinel species of the pollinator community which is exposed to a wide variety of pesticides. In the last half-century, the pesticide most applied worldwide has been the herbicide glyphosate (GLY) used for weed control and with microbiocide effects. After its application in crops, the GLY residues have been detected in flowers visited by honey bees as well as in the stored food of their hives. Therefore, the honey bee brood can ingest the herbicide during larval development. Recent studies proved that GLY has detrimental effects on adult honey bees and other insects associated with the disturbance of their gut microbiota. GLY induces changes in the growth, metabolism and survival of honey bees and stingless bees reared in vitro. However, the effect of GLY on larval microbiota is unknown so far and there are few studies with an in-hive exposure to GLY. For these reasons, this study aims to determine whether GLY induces dysbiosis in honey bee larvae and affects their metamorphosis during the exposure period (pre-defecation) and the post-exposure period. Furthermore, we assessed this herbicide in vitro and in the hive to compare its effects on different rearing procedures. Finally, we tested the pigment BLUE1 as an indirect exposure marker to detect and estimate the in-hive intake concentration of GLY. Our results indicate that the intake of field-relevant concentrations of GLY induced a slowdown in growth with dysbiosis in the larval gut microbiota followed by late effects on their metamorphosis such as teratogenesis and mortality of newly emerged bees. Nevertheless, brood from the same colonies expressed different signs of toxicity depending on the rearing procedure and in a dose-dependent manner.

Microbial Reductive Dechlorination by a Commercially Available Dechlorinating Consortium Is Not Inhibited by Perfluoroalkyl Acids (PFAAs) at Field-Relevant Concentrations.

Perfluoroalkyl acids (PFAAs) have been shown to inhibit biodegradation (i.e., organohalide respiration) of chlorinated ethenes. The potential negative impacts of PFAAs on microbial species performing organohalide respiration, particularly Dehalococcoides mccartyi (Dhc), and the efficacy of in situ bioremediation are a critical concern for comingled PFAA-chlorinated ethene plumes. Batch reactor (no soil) and microcosm (with soil) experiments, containing a PFAA mixture and bioaugmented with KB-1, were completed to assess the impact of PFAAs on chlorinated ethene organohalide respiration. In batch reactors, PFAAs delayed complete biodegradation of cis-1,2-dichloroethene (cis-DCE) to ethene. Maximum substrate utilization rates (a metric for quantifying biodegradation rates) were fit to batch reactor experiments using a numerical model that accounted for chlorinated ethene losses to septa. Fitted values for cis-DCE and vinyl chloride biodegradation were significantly lower (p < 0.05) in batch reactors containing ≥50 mg/L PFAAs. Examination of reductive dehalogenase genes implicated in ethene formation revealed a PFAA-associated change in the Dhc community from cells harboring the vcrA gene to those harboring the bvcA gene. Organohalide respiration of chlorinated ethenes was not impaired in microcosm experiments with PFAA concentrations of 38.7 mg/L and less, suggesting that a microbial community containing multiple strains of Dhc is unlikely to be inhibited by PFAAs at lower, environmentally relevant concentrations.

A combination of the frequent fungicides boscalid and dimoxystrobin with the neonicotinoid acetamiprid in field-realistic concentrations does not affect sucrose responsiveness and learning behavior of honeybees

The increasing loss of pollinators over the last decades has become more and more evident. Intensive use of plant protection products is one key factor contributing to this decline. Especially the mixture of different plant protection products can pose an increased risk for pollinators as synergistic effects may occur. In this study we investigated the effect of the fungicide Cantus® Gold (boscalid/dimoxystrobin), the neonicotinoid insecticide Mospilan® (acetamiprid) and their mixture on honeybees. Since both plant protection products are frequently applied sequentially to the same plants (e.g. oilseed rape), their combination is a realistic scenario for honeybees. We investigated the mortality, the sucrose responsiveness and the differential olfactory learning performance of honeybees under controlled conditions in the laboratory to reduce environmental noise. Intact sucrose responsiveness and learning performance are of pivotal importance for the survival of individual honeybees as well as for the functioning of the entire colony. Treatment with two sublethal and field relevant concentrations of each plant protection product did not lead to any significant effects on these behaviors but affected the mortality rate. However, our study cannot exclude possible negative sublethal effects of these substances in higher concentrations. In addition, the honeybee seems to be quite robust when it comes to effects of plant protection products, while wild bees might be more sensitive.

The Transcriptomic Response of the Boll Weevil, Anthonomus grandis grandis Boheman (Coleoptera: Curculionidae), following Exposure to the Organophosphate Insecticide Malathion.

Insecticide tolerance and resistance have evolved countless times in insect systems. Molecular drivers of resistance include mutations in the insecticide target site and/or gene duplication, and increased gene expression of detoxification enzymes. The boll weevil, Anthonomus grandis grandis Boheman (Coleoptera: Curculionidae), is a pest of commercial cotton and has developed resistance in the field to several insecticides; however, the current organophosphate insecticide, malathion, used by USA eradication programs remains effective despite its long-term use. Here, we present findings from an RNA-seq experiment documenting gene expression post-exposure to field-relevant concentrations of malathion, which was used to provide insight on the boll weevil's continued susceptibility to this insecticide. Additionally, we incorporated a large collection of boll weevil whole-genome resequencing data from nearly 200 individuals collected from three geographically distinct areas to determine SNP allele frequency of the malathion target site, as a proxy for directional selection in response to malathion exposure. No evidence was found in the gene expression data or SNP data consistent with a mechanism of enhanced tolerance or resistance adaptation to malathion in the boll weevil. Although this suggests continued effectiveness of malathion in the field, we identified important temporal and qualitative differences in gene expression between weevils exposed to two different concentrations of malathion. We also identified several tandem isoforms of the detoxifying esterase B1 and glutathione S-transferases, which are putatively associated with organophosphate resistance.

The effects of glyphosate, pure or in herbicide formulation, on bumble bees and their gut microbial communities

The widespread use of glyphosate-based formulations to eliminate unwanted vegetation has increased concerns regarding their effects on non-target organisms, such as honey bees and their gut microbial communities. These effects have been associated with both glyphosate and co-formulants, but it is still unknown whether they translate to other bee species. In this study, we tested whether glyphosate, pure or in herbicide formulation, can affect the gut microbiota and survival rates of the eastern bumble bee, Bombus impatiens. We performed mark-recapture experiments with bumble bee workers from four different commercial colonies, which were exposed to field relevant concentrations of glyphosate or a glyphosate-based formulation (0.01 mM to 1 mM). After a 5-day period of exposure, we returned the bees to their original colonies, and they were sampled at days 0, 3 and 7 post-exposure to investigate changes in microbial community and microbiota resilience by 16S rRNA amplicon sequencing and quantitative PCR. We found that exposure to glyphosate, pure or in herbicide formulation, reduced the relative abundance of a beneficial bee gut bacterium, Snodgrassella, in bees from two of four colonies when compared to control bees at day 0 post-exposure, but this reduction became non-significant at days 3 and 7 post-exposure, suggesting microbiota resilience. We did not find significant changes in total bacteria between control and exposed bees. Moreover, we observed an overall trend in decreased survival rates in bumble bees exposed to 1 mM herbicide formulation during the 7-day post-exposure period, suggesting a potential negative effect of this formulation on bumble bees.

Chronic in-hive exposure to a field-relevant concentration of Closer™ SC (24% sulfoxaflor) insecticide altered immunological and physiological markers of honey bee foragers (Apis mellifera)

Chronic in-hive exposure to a field-relevant concentration of Closer™ SC (24% sulfoxaflor) insecticide altered immunological and physiological markers of honey bee foragers (Apis mellifera)

Structure and function response of bacterial communities towards antibiotic contamination in hyporheic zone sediments

Bacterial communities are crucial for processing and degrading contaminants in hyporheic zones (HZ). However, the effects of antibiotics on HZ bacterial communities have seldom been addressed. Here, using MiSeq 16S amplicon sequencing technology, the effects of acute exposure to Enrofloxacin, Sulfathiazole, Tetracycline hydrochloride, and Penicillin V potassium on HZ bacterial communities were investigated. Results revealed that HZ sediment communities responded differently to different classes of antibiotics, reflecting the distinct selection stress of antibiotics on HZ bacterial communities. Besides, HZ communities from the locations with more severe antibiotic contamination backgrounds (∼150 μg kg−1) were more resistant towards antibiotic treatment. Compared with small/non-significant changes in HZ community diversity and composition treated with ng L−1∼ug L−1 level antibiotics compared to the control group, treatments with antibiotics over mg L−1 level significantly reduced the diversity and changed the structures of HZ bacterial communities, and enhanced the resistance of the community to antibiotics by enriching antibiotic resistant bacteria. The exposure to mg L−1 level antibiotics also changed community functions by restricting the growth of functional bacteria, such as ammonia oxidizing bacteria (AOB) Nitrosomonas, resulting in ammonia accumulation in sediments. The results implied that at field-relevant concentrations, there was no or minor effect of antibiotics on HZ bacterial community structure and functions, and only those areas with high antibiotic concentrations would have effects.

Field and Cage Studies Show No Effects of Exposure to Flonicamid on Honey Bees at Field-Relevant Concentrations.

Simple SummaryThe effects of pesticides on honey bees are of great concern to beekeepers and the general public. In particular, a class of pesticides called neonicotinoids has been found in some studies to affect bee learning and colony function. A pesticide classified as a neonicotinoid, flonicamid, has been detected in the residue analyses of honey and pollen samples for a published study, and that compound was tested at three concentrations (0, 50, and 250 parts per billion (ppb)) in sugar syrup in a field study with bee colonies and in two cage studies. Colony population levels, hive weight changes, thermoregulation, and CO2 concentrations were measured in the field study, and syrup consumption, thermoregulation, and survivorship by worker bees were measured in the cage studies. No significant treatment effects of the pesticide exposure were observed in either the field or the cage studies. These results support the idea that flonicamid is safe for honey bees at these concentrations. Publishing such results when they occur is important, so people use safe pesticides when they need them.The extent to which insecticides harm non-target beneficial insects is controversial. The effects of long-term exposure on honey bees to sublethal concentrations of flonicamid, a pyridinecarboxamide compound used as a systemic insecticide against sucking insects, were examined in a field study and two cage studies. The field study involved the continuous weight, temperature, and CO2 monitoring of 18 honey bee colonies, 6 of which were exposed over six weeks to 50 ppb flonicamid in sugar syrup, 6 exposed to 250 ppb flonicamid in syrup, and 6 exposed to unadulterated syrup (control). Treatments were derived from concentrations observed in honey samples in a published study. No effects were observed on foraging activity, hive weight gain, thermoregulation, or average CO2 concentrations. However, Varroa mite infestations may have also contributed to experimental variability. The two cage studies, in which cages (200 newly-emerged bees in each) were exposed to the same flonicamid concentrations as the field study and kept in a variable-temperature incubator, likewise did not show any experiment-wide effects on survivorship, thermoregulation, or syrup consumption. These results suggest that field applications of flonicamid that result in concentrations as high as 250 ppb in honey may be largely safe for honey bees.

Mapping substrate use across a permafrost thaw gradient

Permafrost thaw in northern peatlands is likely to create a positive feedback to climate change, as microbes transform soil carbon (C) into carbon dioxide (CO2) or methane (CH4). While the microbiome's encoded C-processing potential changes with thaw, the impact on substrate utilization and gas emissions is less well characterized. We therefore examined microbial C-cycling dynamics from a partially thawed Sphagnum-dominated bog to a fully thawed sedge-dominated fen in Stordalen Mire (68.35°N, 19.05°E), Sweden. We profiled C substrate utilization diversity and extent by Biolog Ecoplates™, then tested substrate-specific hypotheses by targeted additions (of glucose, the short chain fatty acids (SCFAs) acetate and butyrate, and the organic acids galacturonic acid and p-hydroxybenzoic acid, all at field-relevant concentrations) under anaerobic conditions at 15 °C. In parallel we characterized microbiomes (via 16S rRNA amplicon sequencing and quantitative polymerase chain reaction) and C gas emissions. The fen exhibited a higher substrate use diversity and faster rate of overall substrate utilization than in the bog, based on Biolog Ecoplate™ incubations. Simple glucose additions (akin to a positive control) to peat microcosms fueled fermentation as expected (reflected in enriched fermenter lineages, their inferred metabolisms, and CO2 production), but also showed potential priming of anaerobic phenol degradation in the bog. Addition of SCFAs to bog and fen produced the least change in lineages and in CO2, and modest suppression of CH4 primarily in the fen, attributed to inhibition. Addition of both organic acids greatly increased the CO2:CH4 ratio in the deep peats but had distinct individual gas dynamics and impacts on microbiota. Both organic acids appeared to act as both C source and as a microbial inhibitor, with galacturonic acid also likely playing a role in electron transfer or acceptance. Collectively, these results support the importance of aboveground-belowground linkages - and in particular the role of Sphagnum spp.- in supplying substrates and inhibitors that drive microbiome assembly and C processing in these dynamically changing systems. In addition, they highlight an important temporal dynamic: responses on the short time scale of incubations (which would reflect transition conditions in the field) differ from those evident at the longer scales of habitat transition, in ways consequential to C gas emissions. In the short term, substrate addition response reflected microbiome legacy (e.g., bog communities were slower to process C and better tolerated inhibitors than fen communities) but led to little overall increase in C gas production (and a high skew to CO2). At the longer time scale of bog and fen thaw stages (which are used to represent these systems in models) the concomitant shifts in plants, hydrology and microbiota attenuate microbiome legacy impacts on substrate processing and C gas emissions over time. As habitat transition areas expand under accelerating change, we hypothesize an increased role of microbiome legacy in the landscape overall, leading to a lag in the increase of CH4 emissions expected from fen expansion.