Sublethal effects of imidacloprid on interactions in a tritrophic system of non-target species

Sublethal pesticide exposure in non-target terrestrial ecosystems: From known effects on individuals to potential consequences on trophic interactions and network functioning

Over the last decades, the intensification of agriculture has resulted in an increasing use of pesticides, which has led to widespread contamination of non-target ecosystems in agricultural landscapes. Plants and arthropods inhabiting these systems are therefore chronically exposed to, at least, low levels of pesticides through direct pesticide drift, but also through the contamination of their nutrient sources (e.g. soil water or host/prey tissues). Pesticides (herbicides, acaricides/insecticides and fungicides) are chemical substances used to control pests, such as weeds, phytophagous arthropods and pathogenic microorganisms. These molecules are designed to disturb specific physiological mechanisms and induce mortality in targeted organisms. However, under sublethal exposure, pesticides also affect biological processes including metabolism, development, reproduction or inter-specific interactions even in organisms that do not possess the molecular target of the pesticide. Despite the broad current knowledge on sublethal effects of pesticides on organisms, their adverse effects on trophic interactions are less investigated, especially within terrestrial trophic networks. In this review, we provide an overview of the effects, both target and non-target, of sublethal exposures to pesticides on traits involved in trophic interactions between plants, phytophagous insects and their natural enemies. We also discuss how these effects may impact ecosystem functioning by analyzing studies investigating the responses of Plant-Phytophage-Natural enemy trophic networks to pesticides. Finally, we highlight the current challenges and research prospects in the understanding of the effects of pesticides on trophic interactions and networks in non-target terrestrial ecosystems.

Transfer and bioaccumulation of pesticides in terrestrial arthropods and food webs: State of knowledge and perspectives for research

Arthropods represent an entry point for pesticide transfers in terrestrial food webs, and pesticide accumulation in upper chain organisms, such as predators can have cascading consequences on ecosystems. However, the mechanisms driving pesticide transfer and bioaccumulation in food webs remain poorly understood. Here we review the literature on pesticide transfers mediated by terrestrial arthropods in food webs. The transfer of pesticides and their potential for bioaccumulation and biomagnification are related to the chemical properties and toxicokinetic of the substances, the resistance and detoxification abilities of the contaminated organisms, as well as by their effects on organisms' life history traits. We further identify four critical areas in which knowledge gain would improve future predictions of pesticides impacts on terrestrial food webs. First, efforts should be made regarding the effects of co-formulants and pesticides mixtures that are currently understudied. Second, progress in the sensitivity of analytical methods would allow the detection of low concentrations of pesticides in small individual arthropods. Quantifying pesticides in arthropods preys, their predators, and arthropods or vertebrates at higher trophic level would bring crucial insights into the bioaccumulation and biomagnification potential of pesticides in real-world terrestrial food webs. Finally, quantifying the influence of the trophic structure and complexity of communities on the transfer of pesticides could address several important sources of variability in bioaccumulation and biomagnification across species and food webs. This narrative review will inspire future studies aiming to quantify pesticide transfers in terrestrial food webs to better capture their ecological consequences in natural and cultivated landscapes.

Impacts of neonicotinoids on biodiversity: a critical review

Neonicotinoids are the most widely used class of insecticides in the world, but they have raised numerous concerns regarding their effects on biodiversity. Thus, the objective of this work was to do a critical review of the contamination of the environment (soil, water, air, biota) by neonicotinoids (acetamiprid, clothianidin, imidacloprid, thiacloprid, thiamethoxam) and of their impacts on terrestrial and aquatic biodiversity. Neonicotinoids are very frequently detected in soils and in freshwater, and they are also found in the air. They have only been recently monitored in coastal and marine environments, but some studies already reported the presence of imidacloprid and thiamethoxam in transitional or semi-enclosed ecosystems (lagoons, bays, and estuaries). The contamination of the environment leads to the exposure and to the contamination of non-target organisms and to negative effects on biodiversity. Direct impacts of neonicotinoids are mainly reported on terrestrial invertebrates (e.g., pollinators, natural enemies, earthworms) and vertebrates (e.g., birds) and on aquatic invertebrates (e.g., arthropods). Impacts on aquatic vertebrate populations and communities, as well as on microorganisms, are less documented. In addition to their toxicity to directly exposed organisms, neonicotinoid induce indirect effects via trophic cascades as demonstrated in several species (terrestrial and aquatic invertebrates). However, more data are needed to reach firmer conclusions and to get a clearer picture of such indirect effects. Finally, we identified specific knowledge gaps that need to be filled to better understand the effects of neonicotinoids on terrestrial, freshwater, and marine organisms, as well as on ecosystem services associated with these biotas.

Imidacloprid Impairs Glutamatergic Synaptic Plasticity and Desensitizes Mechanosensitive, Nociceptive, and Photogenic Response of Drosophila melanogaster by Mediating Oxidative Stress, Which Could Be Rescued by Osthole

Background: Imidacloprid (IMD) is a widely used neonicotinoid-targeting insect nicotine acetylcholine receptors (nAChRs). However, off-target effects raise environmental concerns, including the IMD’s impairment of the memory of honeybees and rodents. Although the down-regulation of inotropic glutamate receptor (iGluR) was proposed as the cause, whether IMD directly manipulates the activation or inhibition of iGluR is unknown. Using electrophysiological recording on fruit fly neuromuscular junction (NMJ), we found that IMD of 0.125 and 12.5 mg/L did not activate glutamate receptors nor inhibit the glutamate-triggered depolarization of the glutamatergic synapse. However, chronic IMD treatment attenuated short-term facilitation (STF) of NMJ by more than 20%. Moreover, by behavioral assays, we found that IMD desensitized the fruit flies’ response to mechanosensitive, nociceptive, and photogenic stimuli. Finally, the treatment of the antioxidant osthole rescued the chronic IMD-induced phenotypes. We clarified that IMD is neither agonist nor antagonist of glutamate receptors, but chronic treatment with environmental-relevant concentrations impairs glutamatergic plasticity of the NMJ of fruit flies and interferes with the sensory response by mediating oxidative stress.

Evaluation of the Toxicity and Sublethal Effects of Acetamiprid and Dinotefuran on the Predator Chrysopa pallens (Rambur) (Neuroptera: Chrysopidae)

Neonicotinoid insecticides affect the physiology or behavior of insects, posing risks to non-target organisms. In this study, the effects of sublethal doses of two neonicotinoid insecticides, acetamiprid and dinotefuran, against Chrysopa pallens (Rambur) (Neuroptera: Chrysopidae) were determined and compared. The results showed that acetamiprid and dinotefuran at LD₁₀ (8.18 ng a.i. per insect and 9.36 ng a.i. per insect, respectively) and LD₃₀ (16.84 ng a.i. per insect and 15.01 ng a.i. per insect, respectively) significantly prolonged the larval stages and pupal stages (except acetamiprid LD₁₀), compared to control. In addition, acetamiprid and dinotefuran at LD₃₀ significantly prolonged the adult preoviposition period (APOP) and total preoviposition period (TPOP). In contrast, the two insecticides at LD₁₀ and LD₃₀ had no significant effect on the longevity, fecundity, reproductive days, preadult survival rate (%), intrinsic rate of increase (r), net reproductive rate (R₀), and finite rate of increase (λ). These results provide a theoretical basis for the rational use of these two insecticides and the utilization and protection of C. pallens.

Newer characters, same story: neonicotinoid insecticides disrupt food webs through direct and indirect effects

During the Green Revolution, older classes of insecticides contributed to biodiversity loss by decreasing insect populations and bioaccumulating across food webs. Introduction of Integrated Pest Management (IPM) improved stewardship of insecticides and promised fewer non-target effects. IPM adoption has waned in recent decades, and popularity of newer classes of insecticides, like the neonicotinoids, has surged, posing new and unique threats to insect populations. In this review, we first address how older classes of insecticides can affect trophic interactions, and then consider the influence of neonicotinoids on food webs and the role they may be playing in insect declines. We conclude by discussing challenges posed by current use patterns of neonicotinoids and how their risk can be addressed.

An update of the Worldwide Integrated Assessment (WIA) on systemic insecticides. Part 2: impacts on organisms and ecosystems

New information on the lethal and sublethal effects of neonicotinoids and fipronil on organisms is presented in this review, complementing the previous Worldwide Integrated Assessment (WIA) in 2015. The high toxicity of these systemic insecticides to invertebrates has been confirmed and expanded to include more species and compounds. Most of the recent research has focused on bees and the sublethal and ecological impacts these insecticides have on pollinators. Toxic effects on other invertebrate taxa also covered predatory and parasitoid natural enemies and aquatic arthropods. Little new information has been gathered on soil organisms. The impact on marine and coastal ecosystems is still largely uncharted. The chronic lethality of neonicotinoids to insects and crustaceans, and the strengthened evidence that these chemicals also impair the immune system and reproduction, highlights the dangers of this particular insecticidal class (neonicotinoids and fipronil), with the potential to greatly decrease populations of arthropods in both terrestrial and aquatic environments. Sublethal effects on fish, reptiles, frogs, birds, and mammals are also reported, showing a better understanding of the mechanisms of toxicity of these insecticides in vertebrates and their deleterious impacts on growth, reproduction, and neurobehaviour of most of the species tested. This review concludes with a summary of impacts on the ecosystem services and functioning, particularly on pollination, soil biota, and aquatic invertebrate communities, thus reinforcing the previous WIA conclusions (van der Sluijs et al. 2015).

Effects of exposure to imidacloprid direct and poisoned cotton aphids Aphis gossypii on ladybird Hippodamia variegata feeding behavior

Imidacloprid is a pesticide used to control aphid infestations of cotton plants. However, poisoned aphids also serve as food for the ladybird natural predator Hippodamia variegata. We investigated whether imidacloprid-treated eggs, pupae, and adults of H. variegata and poisoned aphids altered ladybird predatory behavior. Laboratory bioassay results demonstrated that 0.72 g/L imidacloprid was lethal to ladybirds. Imidacloprid significantly reduced the hatching and emergence rates of H. variegata, and these effects were time and dose dependent. Predation was most adversely affected when the ladybirds directly consumed poisoned aphids and less so when directly exposed to the insecticide at sublethal concentrations. Imidacloprid use in cotton fields should be restricted to the initial stages of aphid infestation to avoid the period when adult ladybirds are present.

Impact of Imidacloprid Soil Drenching on Survival, Longevity, and Reproduction of the Zoophytophagous Predator Podisus maculiventris (Hemiptera: Pentatomidae: Asopinae)

Systemic insecticides when applied as seed treatments or soil drenches are often more toxicologically selective for natural enemies than target pests. This may not be the case, however, for omnivorous predators, which are at risk of extended exposure to systemically applied pesticides through ingestion while feeding on treated plants for nutrients or water. Such exposure may kill or have sublethal consequences for these natural enemies, compromising their role as biocontrol agents of agricultural pest species. The spined soldier bug, Podisus maculiventris (Say) (Hemiptera: Pentatomidae: Asopinae), is an important zoophytophagous biocontrol agent (i.e., able to substitute zoophagy by phytophagy for survival) that may be exposed to systemic insecticides in many agricultural systems. We, therefore, examined effects on P. maculiventris following exposure to cabbage plants subject to soil-drench treatments with imidacloprid, a systemic neonicotinoid insecticide. Predator survival, development, body weight, and reproduction were recorded. Imidacloprid significantly affected nymph survival and adult emergence, but not duration of the nymphal period or adult body weight. At one-twentieth the recommended field rate for whitefly and aphid management, imidacloprid treatments reduced longevity, fecundity, and fertility of female predators. These findings demonstrate that soil treatments with systemic insecticide can negatively impact zoophytophagous natural enemies.

Effects of a Systemic Pesticide Along an Aquatic Tri-Trophic Food Chain

Systemic pesticides, such as the neonicotinoid imidacloprid, can be introduced into aquatic ecosystems through contaminated plant material, which is the basis for detrital (brown) aquatic food-webs. With the aim of exemplarily assessing for indirect effects on the level of predators, we first offered imidacloprid contaminated and uncontaminated alder leaves to the stonefly shredder Protonemura sp. for 72 h. Shredder survival, leaf decomposition, body length and biomass were all between 20% and 50% lower under imidacloprid exposure compared to uncontaminated conditions, indicating physiological implications. Subsequently, these shredders were provided as prey to stonefly predators (Isoperla sp.) kept in cages in a stream. Predator biomass and length decreased by up to 11% and 4.3%, respectively, when feeding on imidacloprid exposed prey. Our study hence suggests that plant material contaminated with systemic pesticides can exert adverse effects in aquatic predators when preying on shredders consuming such leaves, which warrants a further consideration of this pathway.

Effect of Imidacloprid Uptake from Contaminated Soils on Vegetable Growth

In the present study, the effect of imidacloprid uptake from contaminated soils on the growth of leaf vegetable Shanghaiqing was investigated. The result showed that during 35-day exposure, the concentration of imidacloprid (IMI) was in the order of vegetable shoots > vegetable roots > soil, indicating that IMI was more readily concentrated in vegetable shoots than in roots. Moreover, the biomass of IMI-treated vegetable shoots was comparable to that of the controls with early exposure, but was higher than that of the controls after 7-day exposure, showing that the test concentration of IMI could stimulate vegetable growth. The plant metabolic analysis of vegetable shoots using LC-QTOF/MS revealed that IMI may cause oxidative stress to the plant shoots with early exposure; however, the stressful situation of IMI seems to be relieved with the increase of some substances (such as spermidine and phenylalanine) with late exposure. Moreover, the upregulation of N-rich amino acids (glutamine, aspartate, and arginine) suggested that the process of fixing inorganic nitrogen in the plant should be enhanced, possibly contributing to enhanced growth rates. Additionally, four IMI's metabolites were identified by using MS-FINDER software, and the distribution of three metabolites in vegetable tissues was compared.

Contact application of neonicotinoids suppresses the predation rate in different densities of prey and induces paralysis of common farmland spiders

Neonicotinoids are very effective in controlling crop pests but have adverse effects on predators and pollinators. Spiders are less sensitive to neonicotinoids compared to insects because of the different structure of their acetylcholine receptors, the binding targets of neonicotinoids. We tested whether short-term exposure to neonicotinoids affected the predation rate in different densities of prey of spiders and led to their paralysis or eventual death. To examine these effects, we topically exposed dominant epigeic, epiphytic and sheet-weaving farmland spiders to four widely used neonicotinoids (imidacloprid, thiamethoxam, acetamiprid and thiacloprid). We applied the neonicotinoids at concentrations recommended by the manufacturers for spray application under field conditions. Short-term exposure to the formulations of all four tested neonicotinoids had adverse effects on the predation rate of spiders, with imidacloprid (Confidor) associated with the most severe effects on the predation rate and exhibiting partial acute lethality after one hour (15–32%). Acetamiprid also displayed strong sublethal effects, particularly when applied dorsally to Philodromus cespitum. Day-long exposure to dorsally applied acetamiprid or thiacloprid led to paralysis or death of multiple Linyphiidae spp., with the effects particularly prominent in males. To conclude, we provided multiple lines of evidence that short-term exposure to neonicotinoids, which were applied at recommended field concentrations, caused severe health effects or death in multiple families of spiders. Even acetamiprid caused strong effects, despite being subject to less strict regulations in the European Union, compared with those for imidacloprid because of claims of its negligible off-target toxicity.

Imidacloprid Soil Drenches Affect Weight and Functional Response of Spined Soldier Bug (Hemiptera: Pentatomidae)

There are ongoing concerns of potential direct and indirect lethal and sublethal effects of insecticides on nontarget arthropod populations. The risk to natural enemies from systemic insecticides is mainly through exposure to the active ingredient by ingestion, and such risk may be elevated for omnivores that feed on treated plants, as well as herbivores that also feed on those same treated plants. Podisus maculiventris (Say), an important natural enemy in many agricultural systems, can be potentially exposed to the neonicotinoid imidacloprid when ingesting contaminated prey and feeding on plants subjected to soil-drench applications of this compound. In the current study, we examined the potential impact of imidacloprid soil drenches on some functional and morphological endpoints. Cabbage plants were treated with soil drenches of imidacloprid that corresponded to half and full recommended labels rates against whiteflies and aphids. Fourth instar diamondback moth, Plutella xylostella (Linnaeus) (Lepidoptera: Plutellidae), larvae on plants were used as prey in our experiments; P. xylostella is not a target of imidacloprid applications but may co-occur with other pests in systems where the insecticide is applied. We found that exposure to imidacloprid-treated plants did not cause significant mortality neither to P. maculiventris nor to P. xylostella, but both treatment concentrations impaired the predation, with consequences for predator weight gain during the assessment period. Our results corroborate those from other studies and demonstrate that effects from systemic insecticides can transcend trophic levels to affect natural enemies indirectly, such as through exposure from feeding on pests not targeted by the insecticide.

A standardized tritrophic small-scale system (TriCosm) for the assessment of stressor-induced effects on aquatic community dynamics

Chemical impacts on the environment are routinely assessed in single-species tests. They are employed to measure direct effects on nontarget organisms, but indirect effects on ecological interactions can only be detected in multispecies tests. Micro- and mesocosms are more complex and environmentally realistic, yet they are less frequently used for environmental risk assessment because resource demand is high, whereas repeatability and statistical power are often low. Test systems fulfilling regulatory needs (i.e., standardization, repeatability, and replication) and the assessment of impacts on species interactions and indirect effects are lacking. In the present study we describe the development of the TriCosm, a repeatable aquatic multispecies test with 3 trophic levels and increased statistical power. High repeatability of community dynamics of 3 interacting aquatic populations (algae, Ceriodaphnia, and Hydra) was found with an average coefficient of variation of 19.5% and the ability to determine small effect sizes. The TriCosm combines benefits of both single-species tests (fulfillment of regulatory requirements) and complex multispecies tests (ecological relevance) and can be used, for instance, at an intermediate tier in environmental risk assessment. Furthermore, comparatively quickly generated population and community toxicity data can be useful for the development and testing of mechanistic effect models. Environ Toxicol Chem 2018;37:1051-1060. © 2017 SETAC.

Bioassay-guided isolation of potent aphicidal Erythrina alkaloids against Aphis gossypii from the seed of Erythrina crista-galli L

BACKGROUND

The cotton aphid (Aphis gossypii Glover) is one of the most invasive pests of cotton. Many botanical phytochemicals have a long history as a source of insecticides, and as templates for new insecticides. This study was undertaken to isolate aphicidal compounds from the seeds of Erythrina crista-galli L. using the bioassay-guided isolation method.

RESULTS

Three novel and 11 known Erythrina alkaloids were isolated. Erysodine (9), erysovine (10), erysotrine (8) and erythraline (11) showed moderate to excellent aphicidal activity with LD₅₀ values of 7.48, 6.68, 5.13 and 4.67 ng aphid^-1 , respectively. The Potter spray tower bioassay gave corresponding LC₅₀ values of 186.81, 165.35, 163.74 and 112.78 µg ml^-1 . A unique substructure, which presents an sp³ methylene at C-8, a non-oxygenated site at N-9 and a conjugated dienes group (Δ^1,2 and Δ^6,7 ), plays a crucial role in the aphicidal activity. Application of erythraline (11) led to different increases in the activities of superoxide dismutase, catalase and glutathione S-transferase.

CONCLUSION

The study demonstrated that the Erythrina alkaloids erysodine (9), erysovine (10), erysotrine (8) and erythraline (11) have potential use as botanical aphicides for commercial application, or as templates for the development of new insecticides. © 2017 Society of Chemical Industry.

Physicochemical Evidence on Sublethal Neonicotinoid Imidacloprid Interacting with an Odorant-Binding Protein from the Tea Geometrid Moth, Ectropis obliqua

Nowadays the excessive usage of neonicotinoid insecticides always results in residues in Chinese tea fields. It is not clear whether the insecticide residue at the sublethal level influences the physiological processes of tea pests. Here, we provide evidence of interaction between the neonicotinoid imidacloprid and a general odorant-binding protein, EoblGOBP2, from the tea geometrid moth, Ectropis obliqua. The interacting process was demonstrated through multiple fluorescence spectra, UV absorption spectra, circular dichroism (CD) spectra, molecular docking, etc. The binding mode was determined to be static (from 300 to 310 K) and dynamic quenching (from 290 to 300 K). The binding distance was calculated to be 6.9 nm on the basis of FRET theory. According to the thermodynamic analysis, the process was mainly driven by enthalpy (ΔH < 0), and hydrogen bond and van der Waals interactions were the main driving forces in the static and dynamic binding cases, respectively. Moreover, synchronous fluorescence spectra and CD spectra analysis showed stretching of the EoblGOBP2 peptide chains with a decreasing α-helix when imidacloprid was added. Molecular docking was applied and predicted that two hydrogen bonds were formed between imidacloprid and Arg110 in the mature peptide of EoblGOBP2. Moreover, when the absolute amounts of EoblGOBP2 in the moth antennae were measured and calculated by using real-time PCR, it was estimated that imidacloprid at sublethal level (about 0.233 and 0.175 ng/male and female moth antennae, respectively) inhibited the binding of a tea volatile, E-2-hexenal, to EoblGOBP2 at about half. This study indicates that neonicotinoid insecticide at sublethal level may still affect the olfactory cognition of the tea geometrid moth to volatile compounds from tea leaves.