Enantioselective bioaccumulation and toxicological effects of chiral neonicotinoid sulfoxaflor in rats.

Sulfoxaflor is a widely used fourth-generation neonicotinoid pesticide, which has been detected in biological and environmental samples. Sulfoxaflor can potentially be exposed to humans via the food chain, thus understanding its toxic effects and enantioselective bioaccumulation is crucial. In this study, toxicokinetics, bioaccumulation, tissue distribution and enantiomeric profiles of sulfoxaflor in rats were investigated through single oral exposure and 28-days continuous exposure experiment. Sulfoxaflor mainly accumulated in liver and kidney, and the (-)-2R,3R-sulfoxaflor and (-)-2S,3R-sulfoxaflor had higher enrichment than their enantiomers in rats. The toxicological effects were evaluated after 28-days exposure. Slight inflammation in liver and kidney were observed by histopathology. Sphingolipid, amino acid, and vitamin B6 metabolism pathways were significantly disturbed in metabonomics analysis. These toxicities were in compliance with dose-dependent effects. These results improve understanding of enantioselective bioaccumulation and the potential health risk of sulfoxaflor.

Discovery of piperonyl-tethered sulfoximines as novel low bee-toxicity aphicides targeting Amelα1/ratß2 complex.

Nicotinic acetylcholine receptor (nAChR) is recognized as a significant insecticide target for neonicotinoids and some agonists. In this study, the nAChR α1 subunit from Apis mellifera was first found to be narrowly tuned to different bee toxicity insecticides, namely, sulfoxaflor (SFX) and flupyradifurone (FPF). Hence, novel sulfoximine derivatives 7a-h were rationally designed and synthesized by introducing a benzo[d][1,3]dioxole moiety into a unique sulfoximine skeleton based on the binding cavity characteristics of Amelα1/ratß2. The two electrode voltage clamp responses of 7a-h were obviously lower than that of SFX, indicating their potentially low bee toxicity. Besides, representative compounds 7b and 7g exhibited low bee toxicity (LD50 > 11.0 µg/bee at 48 h) revealed by acute contact toxicity bioassays. Molecular modelling results indicated that Ile152, Ala151, and Val160 from honeybee subunit Amelα1 and Lys144 and Trp80 from aphid subunit Mpα1 may be crucial for bee toxicity and aphicidal activity, respectively. These results clarify the toxic mechanism of agonist insecticides on nontargeted pollinators and reveal novel scaffold sulfoximine aphicidal candidates with low bee toxicity. These results will provide a new perspective on the rational design and highly effective development of novel eco-friendly insecticides based on the structure of the nAChR subunit.

Sulfoxaflor influences the biochemical and histological changes on honeybees (Apis mellifera L.).

Pesticide application can have an adverse effect on pollinator honey bees, Apis mellifera L., ranging from mortality to sublethal effects. Therefore, it is necessary to understand any potential effects of pesticides. The present study reports the acute toxicity and adverse effects of sulfoxaflor insecticide on the biochemical activity and histological changes on A. mellifera. The results showed that after 48 h post-treatment, the LD25 and LD50 values were 0.078 and 0.162 µg/bee, respectively, of sulfoxaflor on A. mellifera. The detoxification enzyme activity shows an increase of glutathione-S-transferase (GST) enzyme on A. mellifera in response to sulfoxaflor at LD50 value. Conversely, no significant differences were found in mixed-function oxidation (MFO) activity. In addition, after 4 h of sulfoxaflor exposure, the brains of treated bees showed nuclear pyknosis and degeneration in some cells, which evolved to mushroom shaped tissue losses, mainly neurons replaced by vacuoles after 48 h. There was a slight effect on secretory vesicles in the hypopharyngeal gland after 4 h of exposure. After 48 h, the vacuolar cytoplasm and basophilic pyknotic nuclei were lost in the atrophied acini. After exposure to sulfoxaflor, the midgut of A. mellifera workers showed histological changes in epithelial cells. These findings of the present study showed that sulfoxaflor could have an adverse effect on A. mellifera.

Sulfoxaflor adversely influences the biological characteristics of Coccinella septempunctata by suppressing vitellogenin expression and predation activity.

Sulfoxaflor is a widely used sulfoximine insecticide that has been regarded as an important alternative insecticide for IPM strategies, but a comprehensive study of its potential ecological toxicity is still lacking. In the present work, the growth, longevity, predation and reproduction toxicity of Coccinella septempunctata caused by sulfoxaflor were evaluated. In addition, the potential mechanisms of decreased fecundity in C. septempunctata were investigated by analyzing the transcriptional and protein levels of reproduction-related gene vitellogenin (Vg). In a 20-day acute contact toxicity test, decreased survival proportion, pupation rate, adult emergence ratio, and increased hazard quotient (HQ) values were observed. Moreover, sublethal dosages of sulfoxaflor significantly inhibited the predation, longevity, fecundity and net reproduction rate of progeny. In addition, LR30 of sulfoxaflor dramatically down-regulate the mRNA-expression (F0: 65.38-fold, F1: 2.24-fold) and protein content (F0: 1.35-fold, F1: 1.36-fold) of Vg in the F0 and F1 generations. These results suggested that sulfoxaflor could inhibit the gene and protein content of Vg, thereby reducing the fecundity of C. septempunctata. Our study indicated that sulfoxaflor has potential risks to parent and progeny generations of C. septempunctata. These results provide valuable reference for optimal usage of sulfoxaflor in IPM systems.

The sulfoximine insecticide sulfoxaflor exposure reduces the survival status and disrupts the intestinal metabolism of the honeybee Apis mellifera.

Honeybees (Apis mellifera) are indispensable pollinators in agricultural production, biodiversity conservation, and nutrients provision. The abundance and diversity of honeybees have been rapidly diminishing, possibly related to the extensive use of insecticides in ecosystems. Sulfoxaflor is a novel sulfoximine insecticide that, like neonicotinoids, acts as a competitive modulator of nicotinic acetylcholine receptors (nAChR) in insects. However, few studies have addressed the negative effects of sulfoxaflor on honeybees at environmentally relevant concentrations. In the present study, adult workers were fed a 50% (w/v) of sugar solution containing different concentrations (0, 0.05, 0.5 and 2.0 mg/L) of sulfoxaflor for two weeks consecutively. The survival rates, food intake, and body weight of the honeybees significantly decreased after continuous exposure at higher doses (0.5 and 2.0 mg/L) of sulfoxaflor when compared with the control. The change in the metabolites in the honeybee gut was determined using high-throughput non-targeted metabolomics on day 14 after sulfoxaflor treatment. The results revealed that 24 and 105 metabolites changed after exposure to 0.5 and 2.0 mg/L sulfoxaflor, respectively, compared with that of the control groups. A total of 12 changed compounds including pregenolone and glutathione were detected as potential biomarkers, which were eventually found to be enriched in pathways of the steroid hormone biosynthesis (p = 0.0001) and glutathione metabolism (p = 0.021). These findings provide a new perspective on the physiological influence of sulfoxaflor stress in honeybees.

Sub-lethal doses of sulfoxaflor impair honey bee homing ability.

Agricultural intensification has increased the number of stressors that pollinators are exposed to. Besides increasing landscape fragmentation that limit the supply of flower resources, intensive agricultural practices relying on the use of pesticides to control agricultural pests also affect non-target organisms like honey bees. The use of most pesticides containing neonicotinoids has been severely restricted in the European Union, leaving pesticides containing acetamiprid as the only ones that are still authorized. In the meantime, new substances like sulfoxaflor, that have a similar mode of action acting on the insect's nicotinic acetylcholine receptors (nAChR), have been approved for agricultural use. In Europe and USA, the use of pesticides containing this active ingredient is limited due to toxic effects already reported on bees, but no restrictions regarding this matter were applied in other countries (e.g., Brazil). In this study, homing ability tests with acetamiprid and sulfoxaflor were performed, in which honey bees were fed with three sub-lethal doses from each substance. After exposure, each honey bee was equipped with an RFID chip and released 1 km away from the colony to evaluate their homing ability. No significant effects were detected in honey bees fed with 32, 48 and 61 ng of acetamiprid while a poor performance on their homing ability, with only 28% of them reaching the colony instead of 75%, was detected at a 26 ng/a.s./bee dose of sulfoxaflor. Although, both pesticides act on the nAChR, the higher sulfoxaflor toxicity might be related with the honey bees detoxifying mechanisms, which are more effective on cyano-based neonicotinoids (i.e., acetamiprid) than sulfoximines. With this study we encourage the use of homing ability tests to be a suitable candidate to integrate the future risk assessment scheme, providing valuable data to models predicting effects on colony health that emerge from the individual actions of each bee.

No evidence for impaired solitary bee fitness following pre-flowering sulfoxaflor application alone or in combination with a common fungicide in a semi-field experiment.

Pesticide exposure is considered a major driver of pollinator decline and the use of neonicotinoid insecticides has been restricted by regulatory authorities due to their risks for pollinators. Impacts of new alternative sulfoximine-based compounds on solitary bees and their potential interactive effects with other commonly applied pesticides in agriculture remain unclear. Here, we conducted a highly replicated full-factorial semi-field experiment with the solitary bee Osmia bicornis, an important pollinator of crops and wild plants in Europe, and Phacelia tanacetifolia as a model crop. We show that spray applications of the insecticide sulfoxaflor (product Closer) and the fungicide azoxystrobin (product Amistar), both alone and combined, had no significant negative impacts on adult female survival or the production, mortality, sex ratio and body size of offspring when sulfoxaflor was applied five days before crop flowering. Our results indicate that for O. bicornis (1) the risk of adverse impacts of sulfoxaflor (Closer) on fitness is small when applied at least five days before crop flowering and (2) that azoxystrobin (Amistar) has a low potential of exacerbating sulfoxaflor effects under field-realistic conditions.

Degradation of Sulfoxaflor in Water and Soil: Kinetics, Degradation Pathways, Transformation Product Identification, and Toxicity.

Hydrolysis, photolysis, and soil degradation are important degradation pathways of pesticides and might generate toxic chemicals and pose threats to the environment. Sulfoxaflor is a widely used neonicotinoid pesticide, but few studies have been conducted to research its environmental behaviors and residues. Herein, the hydrolysis and photolysis of sulfoxaflor in water and degradation in four typical Chinese soils were systematically studied. In addition, degradation products, pathways, and toxicity to Daphnia magna were also investigated. Sulfoxaflor can undergo photolysis and soil degradation, and the degradation percentage was greater than 90% after 96 h or 96 days, respectively. However, sulfoxaflor was not degraded or only slightly degraded during in hydrolysis and was not photodegraded in acidic water or sterilized soil. Four degradation products were screened by UHPLC-Q-Orbitrap-HRMS, three candidates (X11719474, X11721061, and X11718922) were synthesized, and the photolysis and soil degradation kinetics were explored. The possible pathways were elucidated. Sulfoxaflor, X11718922, and X11721061 had a low toxicity, and X11719474 (48 h EC50 0.74 mg/L) had a high toxicity to Daphnia magna. Thus, sulfoxaflor and its degradation products could induce tissue damage in Daphnia magna. This work offers a theoretical basis for the application and ecological risk assessment of sulfoxaflor.

Enantioselective bioaccumulation and toxicity of rac-sulfoxaflor in zebrafish (Danio rerio).

Sulfoxaflor is a fourth-generation neonicotinoid insecticide mainly used to control sap-feeding pests. In this study, four stereoisomers of sulfoxaflor were separated using HPLC, and the absolute configurations of three stereoisomers were identified via single-crystal X-ray diffraction. First, the stability and isomerization of the four enantiomers and rac-sulfoxaflor in water and seven organic solvents were investigated. All enantiomers were extremely unstable in water with isomerization rates above 20%. The racemate did not isomerize in any of the solutions and was stable in water (degradation rate less than 7%). Therefore, we studied the acute toxicity, enantioselective behavior, and enzymatic activities of rac-sulfoxaflor in zebrafish. The bioaccumulation experiment demonstrated that the bioconcentration of sulfoxaflor in zebrafish was enantioselective, and the four enantiomers accumulated in zebrafish in the order (+)-2S,3S-sulfoxaflor > (-)-2R,3R-sulfoxaflor > (+)-2R,3S-sulfoxaflor > (-)-2S,3R-sulfoxaflor. The effect of rac-sulfoxaflor on the enzymatic activities of zebrafish showed that superoxide dismutase and glutathione-S-transferase activities and malondialdehyde content were significantly enhanced as compared to those in control, whereas acetylcholinesterase was significantly reduced in the sulfoxaflor exposure treatment (p < 0.05), indicating that sulfoxaflor caused oxidative lesions and induced enzymatic activity in zebrafish. This study provides important information on the enantioselective behavior and toxic effects of sulfoxaflor, which can help assess the potential ecological risk of chiral pesticides to aquatic organisms.

Stereoselective separation of sulfoxaflor by electrokinetic chromatography and applications to stability and ecotoxicological studies.

An Electrokinetic Chromatography method was developed for the stereoselective analysis of sulfoxaflor, a novel sulfoximine agrochemical with two chiral centers. A screening with fourteen negatively charged CDs was performed and Succinyl-ß-CD (Succ-ß-CD) was selected. A 15 mM concentration of this CD in a 100 mM borate buffer (pH 9.0), using an applied voltage of 20 kV and a temperature of 15 °C made possible the baseline separation of the four stereoisomers of sulfoxaflor in 13.8 min. The evaluation of the linearity, accuracy, precision, LODs and LOQs of the method developed showed its performance to be applied to the analysis of commercial agrochemical formulations, the evaluation of the stability of sulfoxaflor stereoisomers under biotic and abiotic conditions, and to predict, for the first time, sulfoxaflor toxicity (using real concentrations instead of nominal concentrations), on two non-target aquatic organisms, the freshwater plant, Spirodela polyrhiza, and the marine bacterium, Vibrio fischeri.

Sublethal effects of Isoclast™ Active (50% sulfoxaflor water dispersible granules) on larval and adult worker honey bees (Apis mellifera L.).

Sulfoxaflor is a novel sulfoximine insecticide which is widely used to control crop pests. Risk assessments have reported its high toxicity to pollinators. However, sulfoxaflor is not persistent in the environment and few studies have addressed its negative effects on larval and newly emerged honeybees at environmentally relevant concentrations. In the present study, the sublethal effects of a sulfoxaflor commercial product, Isoclast™ Active, were evaluated in the laboratory using larvae and newly emerged worker honeybees. The results of 96-h acute toxicity showed that Isoclast is moderately toxic to adult bees, and it could induce significant death and growth failure of larvae after continuous dietary intake. In addition, Isoclast induced significant changes in antioxidative (SOD, CAT), lipid peroxidation (POD, LPO, MDA), detoxification (GST, GR, GSH) and signal transduction-related (AChE, ACh) enzymes or products both in larvae and adult honey bees under residue levels. Here we firstly reported the lethal and sublethal effects of commercial sulfoxaflor to honeybees' larvae and young workers. All these findings revealed the potential risks of sulfoxaflor residue in environment to honey bees, and may also to other pollinators. This is a laboratory mimic studies, and further studies are still needed to investigate the risks and in-depth mechanisms of sulfoxaflor to bees in field.

The Sulfoximine Insecticide Sulfoxaflor and Its Photodegradate Demonstrate Acute Toxicity to the Nontarget Invertebrate Species Daphnia magna.

The environmental fate and persistence of sulfoxaflor is of significant interest given the potential for the insecticide to impact nontarget organisms, particularly pollinating and aquatic species. In the present study we examine the potential for sulfoxaflor, a new sulfoximine insecticide, to undergo degradation and transformation in sediments and the aquatic environment. Following application of the active substance as a foliar spray or seed coating, sulfoxaflor can be found in the soil at a mass percentage of up to 61% of the total applied concentration. The low soil sorption coefficient (KD ) of sulfoxaflor of 0.103 signifies the potential for sulfoxaflor to undergo transport into nearby surface waters via groundwater run-off. In soils and sediments sulfoxaflor produces a sulfoxaflor-urea analog with a varying half-life of 5.0 to 8.5 d depending on the sediment type. Once in surface waters, sulfoxaflor can undergo photolysis to a sulfoxaflor alcohol derivative with a half-life of 35 h. The photodegradate demonstrates reduced aquatic toxicity to Daphnia magna, but the photolytic half-life may be too long to mitigate the acute toxicity of the parent substance sulfoxaflor to D. magna, which was found to have a 48-h median effect concentration of 361 µg/L. Environ Toxicol Chem 2021;40:2156-2164. © 2021 SETAC.

The neonicotinoid alternative sulfoxaflor causes chronic toxicity and impairs mitochondrial energy production in Chironomus kiinensis.

Unintentional environmental consequences caused by neonicotinoids reinforce the development of safer alternatives. Sulfoxaflor is considered such an alternative. However, ecological risk of sulfoxaflor remains largely unknown. Here, we investigated the acute and chronic toxicity of sulfoxaflor to a benthic invertebrate, Chironomus kiinensis. Sulfoxaflor showed lower lethality than imidacloprid to midges, with LC50 values of 84.1 (81.5-87.3), 66.3 (34.8-259), and 47.5 (29.5-306) µg/L for 96-h, 10-d, and 23-d exposures, respectively. Conversely, sulfoxaflor significantly inhibited C. kiinensis growth and emergence in chronic exposures when concentrations were above 20 µg/L. Effects on energy production were assessed through in vitro tests using mitochondria isolated from C. kiinensis. Sulfoxaflor disrupted mitochondrial state-3 respiration, meanwhile, adenosine triphosphatase (ATPase) activity and adenosine triphosphate (ATP) production were both inhibited in a dose-dependent manner. The observed mitochondrial dysfunction may be related to the decreased organismal growth and emergence, which could further influence biodiversity. Interestingly, sulfoxaflor uptake in C. kiinensis was detected even after emergence, implying its potential to be transported along food webs and among environmental compartments. This study provides thorough investigations on the toxicity of an emerging neonicotinoid alternative to Chironomidae. Data derived from the current study are useful to inform future ecological risk assessment and benefit problem-solving to the overall agriculture-environment nexus.

Toxicity of the insecticide sulfoxaflor alone and in combination with the fungicide fluxapyroxad in three bee species.

The sulfoximine insecticide sulfoxaflor is regarded as a potential substitute for neonicotinoids that were recently banned in the EU due to their side effects on bees. Like neonicotinoids, sulfoxaflor acts as a competitive modulator of nicotinic acetylcholine receptors. In agricultural environments, bees are commonly exposed to combinations of pesticides, and neonicotinoids are known to interact synergistically with fungicides. The objective of our study is to assess the acute oral toxicity of sulfoxaflor alone and in combination with a single dose of fluxapyroxad, a succinate dehydrogenase inhibitor (SDHI) fungicide, in three bee species: Apis mellifera, Bombus terrestris and Osmia bicornis. Because synergism may be dose-dependent, we tested a range of sulfoxaflor doses. Synergistic effects were assessed using three different approaches: Bliss criterion of drugs independence, ratio test comparing LD50s and model deviation ratio. Osmia bicornis was the most sensitive species to sulfoxaflor and both O. bicornis and A. mellifera showed significant synergism between the insecticide and the fungicide. For the most part, these synergistic effects were weak and only occurred at early assessment times and intermediate sulfoxaflor doses. The potential ecological relevance of these effects should be confirmed in field and/or cage studies. Overall, our laboratory results demonstrate that sulfoxaflor is somewhat less toxic than the recently banned neonicotinoids imidacloprid, thiamethoxam and clothianidin, but much more toxic than other neonicotinoids (acetamiprid, thiacloprid) still in use in the EU at the time this study was conducted.

Evaluation of sublethal and transgenerational effects of sulfoxaflor on Aphis gossypii via life table parameters and 16S rRNA sequencing.

BACKGROUND: Aphis gossypii, a polyphagous and recurrent pest induced by pesticides, causes tremendous loss crop yields each year. Previous studies on the mechanism of pesticide-induced sublethal effects mainly focus on the gene level. The symbiotic bacteria are also important participants of this mechanism, but their roles in hormesis are still unclear. RESULTS: In this study, life table parameters and 16S rRNA sequencing were applied to evaluate the sublethal and transgenerational effects of sulfoxaflor on adult A. gossypii after 24-h LC20 (6.96 mg L-1 ) concentration exposure. The results indicated that the LC20 of sulfoxaflor significantly reduced the finite rate of increase (λ) and net reproductive rate (R0 ) of parent generation (G0), and significantly increased mean generation time (T) of G1 and G2, but not of G3 and G4. Both reproductive period and fecundity of G1 and G2 were significantly higher than those of the control. Furthermore, our sequencing data revealed that more than 95% bacterial communities were dominated by the phylum Proteobacteria, in which the maximum proportion genus was the primary symbiont Buchnera and the facultative symbiont Arsenophonus. Compared to those of the control, the abundance and composition of symbiotic bacteria of A. gossypii for three successive generations (G0-G2) were changed after G0 A. gossypii was exposed to sulfoxaflor: the diversity of the bacterial community was decreased, but the abundance of Buchnera was increased (G0), while the abundance of Arsenophonus was decreased. Contrary to G0, G1 and G2 cotton aphid exhibited an increased relative abundance of Arsenophonus in the sublethal treatment group. CONCLUSION: Taken together, our results provide an insight into the interactions among pesticide resistance, aphids, and symbionts, which will eventually help to better manage the resurgence of A. gossypii. © 2021 Society of Chemical Industry.

Comparative ecotoxicity of insecticides with different modes of action to Osmia excavata (Hymenoptera: Megachilidae).

Osmia excavata is an important pollinator in commercial fruit orchards. Little information has been published about ecotoxicity to O. excavata, especially the larvae. To clarify the risk of commonly used insecticides with different modes of action to the larvae of O. excavata, six insecticides (clothianidin, acetamiprid, sulfoxaflor, lambda-cyhalothrin, chlorfenapyr and abamectin) were selected for evaluation of their acute lethal toxicity and sublethal effects. Clothianidin and abamectin were the two most toxic insecticides to the larvae of O. excavata with LD50 values of 0.007 (0.006-0.008) and 0.0004 (0.0003-0.0006) µg active ingredient (a.i.) bee-1, respectively. And their ecological risks were high according to the hazard quotient values (HQ > 2500). Sulfoxaflor was identified as the only safe insecticide for O. excavata (HQ < 50) under field conditions. Sublethal toxicity tests showed that larval weight was significantly decreased by ingesting food treated with clothianidin, lambda-cyhalothrin and abamectin (less than the maximum field registered concentrations on fruit trees) due to interference with consumption per larva and reduction of the efficiency of conversion of ingested food. Additionally, above three insecticides significantly prolonged larval developmental duration before cocooning and decreased eclosion rate. Overall, there results suggested that clothianidin and abamectin should not be applied, especially during the flowering phase, the application frequency of lambda-cyhalothrin should be minimized for the purpose of conserving O. excavata. Our results provided important evidences for selecting appropriate insecticides for use in fruit orchards.

Individual and combined impacts of sulfoxaflor and Nosema bombi on bumblebee (Bombus terrestris) larval growth.

Sulfoxaflor is a globally important novel insecticide that can have negative impacts on the reproductive output of bumblebee (Bombus terrestris) colonies. However, it remains unclear as to which life-history stage is critically affected by exposure. One hypothesis is that sulfoxaflor exposure early in the colony's life cycle can impair larval development, reducing the number of workers produced and ultimately lowering colony reproductive output. Here we assess the influence of sulfoxaflor exposure on bumblebee larval mortality and growth both when tested in insolation and when in combination with the common fungal parasite Nosema bombi, following a pre-registered design. We found no significant impact of sulfoxaflor (5 ppb) or N. bombi exposure (50 000 spores) on larval mortality when tested in isolation but found an additive, negative effect when larvae received both stressors in combination. Individually, sulfoxaflor and N. bombi exposure each impaired larval growth, although the impact of combined exposure fell significantly short of the predicted sum of the individual effects (i.e. they interacted antagonistically). Ultimately, our results suggest that colony-level consequences of sulfoxaflor exposure for bumblebees may be mediated through direct effects on larvae. As sulfoxaflor is licensed for use globally, our findings highlight the need to understand how novel insecticides impact non-target insects at various stages of their development.

The Toxic Effects of Sulfoxaflor Induced in Earthworms (Eisenia fetida) under Effective Concentrations.

Sulfoxaflor is a new kind of neonicotinoid insecticide that is used to control sap-feeding insect pests. In this study, a hazard assessment of sulfoxaflor on soil invertebrate earthworms was performed under effective concentrations. The results showed that different exposure times and doses had significant influence on the toxicity of sulfoxaflor. Sulfoxaflor degraded quickly in artificial soil with a degradation rate of 0.002-0.017 mg/(kg·d) and a half-life of 12.0-15.4 d. At 0.5 mg/kg and 1.0 mg/kg, the ·OH- content, antioxidant enzyme activeities, thiobarbituric acid reactive substances (TBARS) content and 8-OHdG content had significant differences compared to those in the control group. On the 56th day, significant differences were only observed in the Glutathione S-transferase enzyme (GST) activity and 8-OHdG content at 1.0 mg/kg compared to those in the control group due to the degradation of sulfoxaflor. This indicated that the risk of sulfoxaflor to earthworms was reduced because it was easily degraded in soil. However, because sulfoxaflor is a super toxic pollutant to earthworms, high concentrations of sulfoxaflor should not be released into the soil environment.

Neonicotinoid and sulfoximine pesticides differentially impair insect escape behavior and motion detection.

Insect nervous systems offer unique advantages for studying interactions between sensory systems and behavior, given their complexity with high tractability. By examining the neural coding of salient environmental stimuli and resulting behavioral output in the context of environmental stressors, we gain an understanding of the effects of these stressors on brain and behavior and provide insight into normal function. The implication of neonicotinoid (neonic) pesticides in contributing to declines of nontarget species, such as bees, has motivated the development of new compounds that can potentially mitigate putative resistance in target species and declines of nontarget species. We used a neuroethologic approach, including behavioral assays and multineuronal recording techniques, to investigate effects of imidacloprid (IMD) and the novel insecticide sulfoxaflor (SFX) on visual motion-detection circuits and related escape behavior in the tractable locust system. Despite similar LD50 values, IMD and SFX evoked different behavioral and physiological effects. IMD significantly attenuated collision avoidance behaviors and impaired responses of neural populations, including decreases in spontaneous firing and neural habituation. In contrast, SFX displayed no effect at a comparable sublethal dose. These results show that neonics affect population responses and habituation of a visual motion detection system. We propose that differences in the sublethal effects of SFX reflect a different mode of action than that of IMD. More broadly, we suggest that neuroethologic assays for comparative neurotoxicology are valuable tools for fully addressing current issues regarding the proximal effects of environmental toxicity in nontarget species.

Target and non-target impact of systemic insecticides on a polyphagous aphid pest and its parasitoid.

Systemic insecticides are used to control agricultural pests globally and their non-target impact at non-lethal doses on beneficial arthropods has been recognized. We assessed the baseline toxicity of imidacloprid, thiamethoxam and sulfoxaflor-based insecticides on the polyphagous aphid pest, Aphis gossypii (Hemiptera: Aphididae), and their non-target effects on its main parasitoid, Aphidius colemani (Hymenoptera: Braconidae), evaluated by residual contact exposure to the median lethal (LC50), the low lethal (LC20) and the sublethal (LC1) concentrations of the three tested insecticides, earlier estimated for the target pest. The results showed that the LC50s for the aphid were 6.4 × 10-3, 5 × 10-3, 2.9 × 10-2 times lower compared to the label concentrations of imidacloprid, thiamethoxam and sulfoxaflor, respectively. LC50 of thiamethoxam caused the highest mortality rate on the parasitoid followed by sulfoxaflor, while imidacloprid had the lowest impact. No significant sublethal effects on reprodution were observed for A. colemani survived to the insecticide exposure. Our findings highlight the importance of case-specific evaluation to optimize pesticide applications in Integrated Pest Management packages taking into account the ecological services provided by biological control agents.