Toxicity and cytotoxicity of the insecticide imidacloprid in the midgut of the predatory bug, Podisus nigrispinus

Exposure to Sublethal Concentrations of Dinotefuran Induces Apoptosis in the Gut of Diaphorina citri Adults via Activating the Mitochondrial Apoptotic Pathway

Diaphorina citri is a serious citrus pest. Dinotefuran is highly insecticidal against D. citri. To analyze the sublethal effects of dinotefuran on D. citri adults, an indoor toxicity test was performed, which revealed that the lethal concentration 50 (LC50) values were 4.23 and 0.50 μg/mL for 24 and 48 h treatments, respectively. RNA-Seq led to the identification of 71 and 231 differentially expressed genes (DEGs) after dinotefuran treatments with LC20 and LC50 doses, respectively. Many of the DEGs are significantly enriched in the apoptosis pathway. Dinotefuran-induced apoptosis in the gut cells was confirmed through independent assays of 4',6-diamidino-2-phenylindole (DAPI) and TdT-mediated dUTP nick end labeling (TUNEL) staining. Increased levels of reactive oxygen species (ROS) and a loss of mitochondrial membrane potential were observed. Four caspase genes were identified, and dinotefuran treatments resulted in increased mRNA levels of DcCasp1 and DcCasp3a. These findings shed light on the sublethal effects of dinotefuran on D. citri.

Thymol's modulation of cellular macromolecules, oxidative stress, DNA damage, and NF-kB/caspase-3 signaling in the liver of imidacloprid-exposed rats

We evaluated whether thymol (THY) (30 mg/kg b.wt) could relieve the adverse effects of the neonicotinoid insecticide imidacloprid (IMD) (22.5 mg/kg b.wt) on the liver in a 56-day oral experiment and the probable underlying mechanisms. THY significantly suppressed the IMD-associated increase in hepatic enzyme leakage. Besides, the IMD-induced dyslipidemia was considerably corrected by THY. Moreover, THY significantly repressed the IMD-induced hepatic oxidative stress, lipid peroxidation, DNA damage, and inflammation. Of note, the Feulgen, mercuric bromophenol blue, and PAS-stained hepatic tissue sections analysis declared that treatment with THY largely rescued the IMD-induced depletion of the DNA, total proteins, and polysaccharides. Moreover, THY treatment did not affect the NF-kB p65 immunoexpression but markedly downregulated the Caspase-3 in the hepatocytes of the THY+IMD-treated group than the IMD-treated group. Conclusively, THY could efficiently protect against IMD-induced hepatotoxicity, probably through protecting cellular macromolecules and antioxidant, antiapoptotic, and anti-inflammatory activities.

Pharmacotherapeutic potential of malvidin to cure imidacloprid induced hepatotoxicity via regulating PI3K/AKT, Nrf-2/Keap-1 and NF-κB pathway

Imidacloprid (IMI) is one of the top-notch insecticides that adversely affects the body organs including the liver. Malvidin (MAL) is a natural flavonoid which exhibits a wide range of pharmacological properties. This research was designed to evaluate the protective ability of MAL to counteract IMI instigated liver toxicity in rats. Thirty-two rats were divided into four groups including control, IMI (5mg/kg), IMI (5mg/kg) + MAL (10mg/kg) and MAL (10mg/kg) alone treated group. The recommended dosages were administrated through oral gavage for 4 weeks. It was revealed that IMI intoxication disrupted the PI3K/AKT and Nrf-2/Keap-1 pathway. Furthermore, the activities of catalase (CAT), glutathione peroxidase (GPx), superoxide dismutase (SOD), heme-oxygenase-1 (OH-1) and glutathione reductase (GSR) were reduced while upregulating reactive oxygen species (ROS) and malondialdehyde (MDA) levels after IMI treatment. Moreover, IMI poisoning increased the levels of ALT (Alanine aminotransferase), AST (Aspartate transaminase), and ALP (Alkaline phosphatase) while reducing the levels of total proteins and albumin in hepatic tissues of rats. Besides, IMI administration escalated the expressions of Bcl-2-associated protein x (Bax) and cysteine-aspartic acid protease-3 (Caspase-3) while downregulating the expressions of B-cell lymphoma 2 (Bcl-2). Similarly, IMI intoxication, increased the levels of Interleukin-6 (IL-6), Nuclear factor kappa-B (NF-κB), Interleukin-1β (IL-1β), tumor necrosis factor-α (TNF-α), and the activity of cyclooxygenase-2 (COX-2). Furthermore, IMI disrupted the normal architecture of hepatic tissues. However, MAL treatment remarkably protected the liver tissues via regulating abovementioned disruptions.

Advances in the Integrated Pest Management of Quinoa (Chenopodium quinoa Willd.): A Global Perspective

Since ancestral times, quinoa (Chenopodium quinoa Willd.) has been cultivated in the Andean regions. Recently, this pseudocereal has received increasing international attention due to its beneficial properties, such as adaptation and resilience in the context of global change, and the nutritional value of the grains. As a result, its production areas have not only increased in the highlands of South America but have also expanded outside of its Andean origins, and the crop is currently produced worldwide. The key pests of quinoa in the Andean region are the gelechiid moths Eurysacca melanocampta and Eurysacca quinoae; in other parts of the world, new pest problems have recently been identified limiting quinoa production, including the gelechiid Scrobipalpa atripicella in North America and Europe and the agromyzid fly Amauromyza karli in North America. In this review, the status of quinoa pests in the world is presented, and different aspects of their integrated management are discussed, including sampling methodologies for pest monitoring, economic threshold levels, and various control strategies.

Effects of the insecticide flupyradifurone on Anticarsia gemmatalis caterpillar and its predator Podisus nigrispinus

The caterpillar Anticarsia gemmatalis (Lepidoptera: Noctuidae) is a prevalent pest in soybean plantations, managed using both natural and synthetic chemical products. However, the emergence of resistance in some populations emphasizes the need to explore alternative insecticides. Flupyradifurone, a neurotoxic insecticide, has not been previously used for controlling A. gemmatalis. This study evaluated the potential of flupyradifurone in the management of A. gemmatalis. Initially, the toxicity and anti-feeding effects, as well as histopathological and cytotoxic impacts, of flupyradifurone on A. gemmatalis were evaluated. Subsequently, the indirect effects of flupyradifurone on the midgut and fat body of the predator Podisus nigrispinus (Hemiptera: Pentatomidae) were verified. The results indicate the susceptibility of caterpillars to flupyradifurone, with an LC50 of 5.10 g L-1. Furthermore, the insecticide adversely affects survival, induces an anti-feeding response, and inflicts damage on the midgut of the caterpillars. However, flupyradifurone also leads to side effects in the predator P. nigrispinus through indirect intoxication of the caterpillars, including midgut and fat body damage. While flupyradifurone demonstrates toxicity to A. gemmatalis, suggesting its potential for the chemical control of this pest, the indirect negative effects on the predator indicate the need for its controlled use in integrated pest management programs with the insecticide and the predator.

Current Insights into Sublethal Effects of Pesticides on Insects

The effect of pesticides on insects is often discussed in terms of acute and chronic toxicity, but an important and often overlooked aspect is the impact of sublethal doses on insect physiology and behavior. Pesticides can influence various physiological parameters of insects, including the innate immune system, development, and reproduction, through a combination of direct effects on specific exposed tissues and the modification of behaviors that contribute to health and reproductive success. Such behaviors include mobility, feeding, oviposition, navigation, and the ability to detect pheromones. Pesticides also have a profound effect on insect learning and memory. The precise effects depend on many different factors, including the insect species, age, sex, caste, physiological condition, as well as the type and concentration of the active ingredients and the exposure route. More studies are needed to assess the effects of different active ingredients (and combinations thereof) on a wider range of species to understand how sublethal doses of pesticides can contribute to insect decline. This review reflects our current knowledge about sublethal effects of pesticides on insects and advancements in the development of innovative methods to detect them.

Behavioral and Transcriptomic Analyses in the Indoxacarb Response of a Non-Target Damselfly Species

Ischnura senegalensis, which widely spreads in paddy fields, has the potential to be used as a natural predator of insect pests. However, the application of insecticides in the field could pose a threat to the survival of I. senegalensis. Among these pesticides, indoxacarb, an oxadiazine insecticide, is renowned for its broad-spectrum efficacy against numerous insect pests. In this study, we examined the toxicity of indoxacarb towards the larvae of I. senegalensis. Behavioral experiments and transcriptome analyses were conducted under indoxacarb treatments. Results revealed that indoxacarb induced abnormal body gestures and significant locomotory impairments, which could ultimately reduce the survival rate of the larvae in their natural habitat. Moreover, transcriptome analyses indicated that genes related to muscle function were significantly affected. Interestingly, at lower concentrations of indoxacarb (0.004 mg/L), the larvae seem to detoxify the indoxacarb with the aid of the cytochrome P450 gene. However, under higher concentrations (0.4 mg/L), the sensory abilities of the larvae were significantly diminished, and they were unable to degrade the toxicity of indoxacarb. Our study underscores the importance of carefully evaluating the impact of insecticides on non-target predatory insects before their widespread application.

Thymol abates the detrimental impacts of imidacloprid on rat brains by lessening oxidative damage and apoptotic and inflammatory reactions

Imidacloprid (IMID) is one of the most widely used neonicotinoid insecticides globally and, consequently, a probable widespread environmental contaminant. The potential neurotoxic effects of IMID have been previously reported. This study aimed to investigate the possible beneficial effect of thymol (TML) in relieving IMID-induced harmful effects on the brain of male Sprague-Dawley rats. For this aim, four groups (10 rats/group) were orally administered corn oil, TML (30 mg/kg b.wt), IMID (22.5 mg/kg b.wt), or TML + IMID for 56 days. The brain tissues were biochemically, histopathologically, and immunohistochemically evaluated. The results displayed that TML significantly restored the IMID-induced depletion of the total antioxidant capacity of the brain tissues. At the same time, the IMID-associated increased levels of lipid peroxidation in terms of malondialdehyde content were markedly suppressed in the TML + IMID group. Also, TML oral dosing markedly reduced the release of inflammatory elements, including nitric oxide and myeloperoxidase, resulting from IMID exposure. Furthermore, the IMID-induced decrease in gamma-aminobutyric acid but the increase in acetylcholinesterase was considerably reversed by TML oral dosing. Additionally, TML oral administration significantly counteracted the IMID-induced brainepatic DNA damage, as revealed by the comet assay. Besides, a significant downregulatibrainepatic Caspase-3 was evident in the TML + IMID group compared to the IMID group. However, TML oral dosing has not significantly altered the IMID-induced nuclear factor (NF-κB p65) increase. Therefore, TML could be a protective agent against IMID-induced detrimental impacts on brain tissue, possibly through its antioxidant, antiapoptotic, and anti-inflammatory activities.

Insights into the ubiquity, persistence and microbial intervention of imidacloprid

Imidacloprid, a neonicotinoid pesticide, is employed to increase crop productivity. Meanwhile, its indiscriminate application severely affects the non-target organisms and the environment. As an eco-friendly and economically workable option, the microbial intervention has garnered much attention. This review concisely outlines the toxicity, long-term environmental repercussions, degradation kinetics, biochemical pathways, and interplay of genes implicated in imidacloprid remediation. The studies have highlighted imidacloprid residue persistence in the environment for up to 3000 days. In view of high persistence, effective intervention is highly required. Bacteria-mediated degradation has been established as a viable approach with Bacillus spp. being among the most efficient at 30 ℃ and pH 7. Further, a comparative metagenomic investigation reveals dominant neonicotinoid degradation genes in agriculture compared to forest soils with distinctive microbial communities. Functional metabolism of carbohydrates, amino acids, fatty acids, and lipids demonstrated a significantly superior relative abundance in forest soil, implying its quality and fertility. The CPM, CYP4C71v2, CYP4C72, and CYP6AY3v2 genes that synthesize cyt p450 monooxygenase enzyme play a leading role in imidacloprid degradation. In the future, a systems biology approach incorporating integrated kinetics should be utilized to come up with innovative strategies for moderating the adverse effects of imidacloprid on the environment.

The fungicide azoxystrobin causes histopathological and cytotoxic changes in the midgut of the honey bee Apis mellifera (Hymenoptera: Apidae)

Apis mellifera is an important bee pollinating native and crop plants but its recent population decline has been linked to the use of pesticides, including fungicides that have been commonly classified as safe for bees. However, many pesticides, in addition to direct mortality cause sublethal effects, including damage to target selective honey bee organs. The midgut is the organ responsible for the digestion and absorption of nutrients and the detoxification of ingested substances, such as pesticides. This study evaluated the histopathological and cytotoxic changes in the midgut of A. mellifera workers caused by the pesticide azoxystrobin. The limit-test was performed, and a 100 µg a.i./bee dose was administered orally and midgut analyzed with light and transmission electron microscopies after 24 h and 48 h of pesticide exposure. The midgut of the control bees has a single layer of digestive cells, with spherical nuclei, nests of regenerative cells, and the lumen coated with the peritrophic matrix. The bees fed on azoxystrobin showed morphological changes, including intense cytoplasm vacuolization and cell fragments released into the gut lumen. The protein detection test showed greater staining intensity in the nests of regenerative cells after 24 h of exposure to azoxystrobin. The occurrence of damage to the midgut in A. mellifera exposed to azoxystrobin indicates that although this fungicide has been classified as low toxicity for bees, it has sublethal effects in the midgut, and effects in other organs should be investigated.

Adsorption and Photocatalytic Degradation of Pesticides into Nanocomposites: A Review

The extensive use of pesticides in agriculture has significantly impacted the environment and human health, as these pollutants are inadequately disposed of into water bodies. In addition, pesticides can cause adverse effects on humans and aquatic animals due to their incomplete removal from the aqueous medium by conventional wastewater treatments. Therefore, processes such as heterogeneous photocatalysis and adsorption by nanocomposites have received special attention in the scientific community due to their unique properties and ability to degrade and remove several organic pollutants, including pesticides. This report reviews the use of nanocomposites in pesticide adsorption and photocatalytic degradation from aqueous solutions. A bibliographic search was performed using the ScienceDirect, American Chemical Society (ACS), and Royal Society of Chemistry (RSC) indexes, using Boolean logic and the following descriptors: "pesticide degradation" AND "photocatalysis" AND "nanocomposites"; "nanocomposites" AND "pesticides" AND "adsorption". The search was limited to research article documents in the last ten years (from January 2012 to June 2022). The results made it possible to verify that the most dangerous pesticides are not the most commonly degraded/removed from wastewater. At the same time, the potential of the supported nanocatalysts and nanoadsorbents in the decontamination of wastewater-containing pesticides is confirmed once they present reduced bandgap energy, which occurs over a wide range of wavelengths. Moreover, due to the great affinity of the supported nanocatalysts with pesticides, better charge separation, high removal, and degradation values are reported for these organic compounds. Thus, the class of the nanocomposites investigated in this work, magnetic or not, can be characterized as suitable nanomaterials with potential and unique properties useful in heterogeneous photocatalysts and the adsorption of pesticides.

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.

Indoxacarb effects on non-target predator, Podisus distinctus (Hemiptera: Pentatomidae)

Forestry pest management includes biological and chemical methods of pest control. Using insecticides and natural enemies can be compatible in forest pest management programs. The compatibility of the predatory stink bug Podisus distinctus with the insecticide indoxacarb, used in forestry, needs to be evaluated in Brazil. This study investigated the mortality, survival, respiration, preference, prey consumption, and locomotor activity of P. distinctus adults exposed to indoxacarb. In concentration-mortality bioassays, the lethality of indoxacarb (LC₅₀ = 2.62 g L^-1 and LC₉₀ = 6.11 g L^-1) was confirmed in P. distinctus adults. The survival rate was 100% in predator insects not exposed to indoxacarb, declining to 40.7% in predator insects exposed to 2.62 g L^-1 and 0.1% in predators treated with 6.11 g L^-1. Indoxacarb reduced the respiration of P. distinctus from 18.45 to 14.41 µL CO₂ h^-1 at 2.62 g L^-1 for up to 3 h after insecticide exposure, inhibiting food consumption and displaying hyperexcitation. The harmful effects of indoxacarb to the natural enemy suggest that it should be better assessed for use with P. distinctus for pest management in forestry.

Acute oral exposure to imidacloprid induces apoptosis and autophagy in the midgut of honey bee Apis mellifera workers

The honey bee Apis mellifera is an important pollinator that increases the yield and quality of crops. In recent years, honey bee populations have declined in some parts of the world, which has been associated with several causes, including pesticides used in agriculture. Neonicotinoids are neurotoxic insecticides widely used in the world with systemic action mode contaminating nectar and pollen that may be consumed by bees. This study evaluated the side effects of imidacloprid in the midgut of A. mellifera after acute oral exposure. Toxicity, histopathology, cytotoxicity, and expression of autophagy-related gene atg1 were evaluated in honey bee workers orally exposed to imidacloprid. The estimated imidacloprid LC₅₀ was 1.44 mg L^-1. The midgut epithelium of bees fed on imidacloprid LC₅₀ has the occurrence of cytoplasm vacuoles, enlarged intercellular spaces, disorganization of the striated border, and nuclear pyknosis, with an organ injury index that increases with time exposure. The midgut digestive cells of treated bees have apical protrusions, damaged mitochondria, and autophagosomes that were characterized for content with organelle debris and high expression of atg1. These features indicate the occurrence of high cell death in the midgut of workers exposed to imidacloprid, which may affect the digestibility the physiology of the insect.

Side-effects of pesticides on non-target insects in agriculture: a mini-review

Climate change mediated by anthropogenic activity induces significant alterations on pest abundance and behavior and a potential increase in the use of agrochemicals for crop protection. Pesticides have been a tool in the control of pests, diseases, and weeds of agricultural systems. However, little attention has been given to their toxic effects on beneficial insect communities that contribute to the maintenance and sustainability of agroecosystems. In addition to pesticide-induced direct mortality, their sublethal effects on arthropod physiology and behavior must be considered for a complete analysis of their impact. This review describes the sublethal effects of pesticides on agriculturally beneficial insects and provides new information about the impacts on the behavior and physiology of these insects. The different types of sublethal effects of pesticides used in agriculture on pollinators, predators, parasitoids, and coprophagous insects were detailed.

Susceptibility of Demotispa neivai (Coleoptera: Chrysomelidae) to Beauveria bassiana and Metarhizium anisopliae entomopathogenic fungal isolates

BACKGROUND

The potential of Beauveria bassiana and Metarhizium anisopliae isolates obtained from naturally infected oil palm pests was evaluated to control Demotispa neivai as an alternative for organophosphate insecticide use in oil palm crops in Latin America. Two B. bassiana (Bb-0018 and Bb-0025) and two M. anisopliae (Ma-0002 and Ma-0003) isolates were tested against D. neivai adults for hydrophobicity, virulence, survival, adhesion to host cuticle, and mortality in semi-field conditions.

RESULTS

Concentration-mortality bioassays demonstrate that isolates had lethal effect on D. neivai adults with Bb-0025 [median lethal concentration (LC₅₀ ) = 3.45 × 10⁷ conidia mL^-1 ] and Bb-0018 (LC₅₀  = 3.75 × 10⁷ conidia mL^-1 ) being the most effective followed by Ma-0003 (LC₅₀  = 3.38 × 10⁸ conidia mL^-1 ) and Ma-0002 (5.33 × 10⁸ conidia mL^-1 ). Adult survival was 99% without exposure to fungal isolates, decreasing to 21.65% in insects exposed to Ma-0002, 19.41% with Ma-0003, 20.13% with Bb-0018, and 0.17% with Bb-0025. Mortality of D. neivai adults caused by the entomopathogenic fungal isolates was similar in both laboratory and semi-field conditions. Also, vegetative growth of the entomopathogenic fungal isolates was found in infected D. neivai adults in the field.

CONCLUSION

Our data suggest that the tested entomopathogenic fungal isolates are effective against D. neivai with potential to be used as biological control agents contributing to the decrease of the use of chemical insecticides to control this oil palm pest. © 2021 Society of Chemical Industry.

Sublethal Effects of Imidacloprid on Fecundity, Apoptosis and Virus Transmission in the Small Brown Planthopper Laodelphax striatellus

Laodelphax striatellus damages plants directly through sucking plant sap and indirectly as a vector of rice stripe virus (RSV), resulting in serious losses of rice yield. It is one of the most destructive insects of rice in East Asia. Insecticides are primarily used for pest management, but the sublethal concentrations of insecticides may benefit several insects. The present research attempted to explore the effects of sublethal concentrations of imidacloprid on the fecundity, apoptosis and RSV transmission in the viruliferous SBPH. The results showed that the fecundity of SBPH was significantly increased after treatment with the LC₁₀ dose of imidacloprid, while the LC₃₀ dose of imidacloprid reduced the fecundity compared with the control. To further investigate the underlying mechanism of increased fecundity after exposure to the LC₁₀ dose of imidacloprid, we examined the expression levels of vitellogenin (Vg), Vg receptor (VgR) and caspases in the ovaries of SBPH, and observed the apoptosis by terminal deoxynucleotidyl transferase (TDT)-mediated dUTP-digoxigenin nick end labeling (TUNEL). qRT-PCR results indicated that the expression levels of Vg, VgR and four caspase genes were all significantly increased by the LC₁₀ dose of imidacloprid, and TUNEL assays suggested that the frequency of apoptosis was significantly higher in the SBPH treated by the LC₁₀ dose of imidacloprid, suggesting a potential correlation between the increased fecundity and the apoptosis of SBPH ovarioles. Additionally, the expression levels of RNA3 and capsid protein (CP) were both increased significantly by the LC₁₀ dose of imidacloprid, whereas were decreased by the LC₃₀ dose of imidacloprid compared to the control. Therefore, this study clarifies the mechanisms of sublethal effects of imidacloprid on viruliferous SBPH and could be used to optimize pest control strategies.

Exposure to insecticides causes effects on survival, prey consumption, and histological changes in the midgut of the predatory bug, Podisus nigrispinus (Hemiptera: Pentatomidae)

The control of defoliating caterpillars in forestry includes the use of insecticides and releases of the predatory bug Podisus nigrispinus, but some compounds may affect non-target natural enemies, which need evaluation of risk assessment. This research investigates the survival, preference, and prey consumption of P. nigrispinus adults fed with prey treated with the lethal concentration (LC₅₀) of Bacillus thuringiensis (Bt), permethrin, tebufenozide, and thiamethoxam. Moreover, midgut histopathology of P. nigrispinus fed with preys treated with LC₅₀ of each insecticide was investigated. The insecticides Bt, permethrin, and thiamethoxam reduce the survival and the prey consumption in P. nigrispinus fed with preys contaminate with these chemicals. However, the four tested insecticides, including tebufenozide, cause histological changes such as irregular epithelial architecture, cytoplasm vacuolization, and release of cell fragments in the midgut lumen of P. nigrispinus. The sublethal effects of Bt, permethrin, tebufenozide, and thiamethoxam to the natural enemy suggest that they should be better evaluated to be used together with P. nigrispinus for integrated pest management in forestry.

Behavioral and ultrastructural effects of novaluron on Aedes aegypti larvae

Chitin synthesis inhibitors (CSI) are supposed to inhibit formation of chitin microfibrils in newly synthesized cuticle during molting process. Conversely, there has been comparatively few data on morphological effects of CSI on non-target insect organs. In this work, the effects of the CSI novaluron on behavior and midgut of A. aegypti were evaluated. Toxicity bioassays revealed that novaluron is toxic to A. aegypti larva with LC₅₀ = 18.57 mg L^-1 when exposed in aqueous solution for 24 h. Novaluron treated larvae were less active and spent more time resting compared to the control group. Histopathology showed that midguts of novaluron-treated larvae had cytoplasm vacuolization and damaged brush border. Cytotoxic effects in midguts of treated larvae induced necrosis, autophagy and damage to mitochondria. Despite being chitin synthesis inhibitor, novaluron did not induce alterations in the integument of A. aegypti larvae. Fluorescence microscopy revealed that the number of digestive cells were higher in novaluron-treated larvae than in control, in response to digestive cell apoptosis. The present study highlights the importance of novaluron against A. aegypti larvae by causing injuries to non-target organs, altering behaviors, inducing cell death and inhibiting cell proliferation.

Deltamethrin-Mediated Effects on Locomotion, Respiration, Feeding, and Histological Changes in the Midgut of Spodoptera frugiperda Caterpillars

Simple Summary

Spodoptera frugiperda is controlled mainly with chemical insecticides. Toxicity, survival, respiration, mobility, anti-feeding effect, and histology of the midgut of S. frugiperda caterpillars exposed to deltamethrin were evaluated. Deltamethrin was toxic to third-instar caterpillars, decreasing survival. The insecticide reduces the respiratory rate and food consumption, and causes repellency. Exposure to deltamethrin causes histological alterations in the midgut, damaging the digestive cells and peritrophic matrix. Deltamethrin is toxic to S. frugiperda caterpillars, causing mortality, alteration of locomotor behavior, reduced respiration and feeding, and irreversible damage to the midgut epithelium.

Abstract

Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae) is the main pest of maize crops, and effective methods for pest management are needed. The insecticidal efficacy of deltamethrin was evaluated against S. frugiperda for toxicity, survival, locomotion, anti-feeding, and histological changes in the midgut. Concentration–mortality bioassays confirmed that deltamethrin (LC₅₀ = 3.58 mg mL⁻¹) is toxic to S. frugiperda caterpillars. The survival rate was 99.7% in caterpillars not exposed to deltamethrin, decreasing to 50.3% in caterpillars exposed to LC₅₀, and 0.1% in caterpillars treated with LC₉₀. Spodoptera frugiperda demonstrated reduced mobility on deltamethrin-treated surfaces. Deltamethrin promoted a low respiration rate of S. frugiperda for up to 3 h after insecticide exposure, displaying immobilization and inhibiting food consumption. Deltamethrin induces histological alterations (e.g., disorganization of the striated border, cytoplasm vacuolization, and cell fragmentation) in the midgut, damaging the digestive cells and peritrophic matrix, affecting digestion and nutrient absorption.

Pendimethalin-based herbicide impairs cellular immune response and haemocyte morphology in a beneficial ground beetle

Herbicides have become the most commonly applied agrochemicals in agroecosystems. Thus, basic knowledge of their physiological effects on insects is needed, especially for understanding their impact on beneficial insect species. In this study, we evaluated the effect of a pendimethalin-based herbicide (PND) on the cellular immune response of the carabid beetle Harpalus (Pseudoophonus) rufipes (De Geer 1774) (Coleoptera, Carabidae), acting as biocontrol agent in agroecosystems. Total and differential haemocyte counts and phagocytosis assay, performed by injecting in vivo carboxylate-modified polystyrene latex beads, were measured in beetles exposed to a recommended field dose (4L per ha) of PND to evaluate the exposure effects over the time. The pattern of haemocyte subpopulations and the decrease of the phagocytic index after the exposure to PND suggested a lowering of P. rufipes ability to face an infection performing a cell-mediated response. PND was also found to cause cytotoxic effects on the haemocyte ultrastructure. Ultrastructural alterations such as irregular shape, large vacuolization of the cytoplasm, and condensation of marginated chromatin were recorded from 2d of exposure. The loss of RER, Golgi apparatus, mitochondria integrity and the swelling of the outer nuclear membrane found in some haemocytes suggested an interference of PND with the membrane permeability. Results indicated that the exposure to PND impairs the distribution, morphology and physiological functions of haemocytes causing a decrease of P. rufipes immunocompetence. Moreover, the sensitivity to herbicide exposure makes this species a suitable model and a useful bioindicator for monitoring exposure effects on non-target species. This study provides useful information to protect and preserve biodiversity of insects in agroecosystems.

Imidacloprid-mediated alterations on the salivary glands of the Neotropical brown stink bug, Euschistus heros

The management of the Neotropical brown stinkbug Euschistus heros (Hemiptera: Pentatomidae) in soybean fields has been heavily dependent on the application of neonicotinoid insecticides. Neonicotinoids act primarily by impairing the function of the nicotinic acetylcholine receptors of the nervous system. These compounds also target specific organs (e.g., salivary glands), which may potentiate their insecticidal efficacy. Here, we evaluated whether the exposure to the neonicotinoid imidacloprid would cause cytomorphological changes in the salivary glands of E. heros. First, we determined the lethal concentrations (LCs) of imidacloprid through contact and ingestion. Subsequently, the cytomorphology of the salivary glands were evaluated in insect groups that survived exposure to the LC₅ (3.75 mg a.i./L), LC₅₀ (112.5 mg a.i./L), or LC₇₅ (375.0 mg a.i./L, equivalent to the recommended field rate) doses. Imidacloprid induced apoptosis and necrosis in the salivary gland cells according to the insecticide concentration and salivary gland region. All concentrations increased apoptosis and injured cells (e.g., vacuolization, chromatin condensation, swelling of organelles, and plasma membrane rupture) in the principal and accessory salivary glands. Individuals that survived exposure to the highest concentrations (i.e., LC₅ and LC₅₀) were more affected, and exhibited several necrotic cells on their main principal salivary glands. Collectively, our results indicate that imidacloprid exerts toxic effects on the non-target organs, such as the salivary glands, which increases the efficacy of this compound in the management of stink bug infestations.

Spiromesifen induces histopathological and cytotoxic changes in the midgut of the honeybee Apis mellifera (Hymenoptera: Apidae)

The honeybee Apis mellifera is an important pollinator that, similarly to other bees, undergoes colony losses due to several problems, including the use of pesticides in the agriculture. In addition to direct mortality, pesticides cause side-effects in some non-target organs, such as the midgut, which is the main organ for digestion and absorption. Spiromesifen is a pesticide used to control mites and whiteflies, which can be ingested by bees feeding on contaminated floral resources. This study evaluated the histopathological and cytological effects of the ingestion of spiromesifen on the midgut of A. mellifera workers. The bees were exposed per os to the field recommended dose of spiromesifen, and the midgut was analyzed after 24h and 48h of exposure to the pesticide. The midgut has a single layer of digestive cells, with spherical nucleus, nests of regenerative cells and layers of peritrophic matrix in the lumen. Bees treated with spiromesifen presented histological and cytological changes in the midgut, including disorganization of the epithelial architecture, release of cell fragments to the lumen, accumulation of mitochondria in the apical cytoplasm, alteration of the basal labyrinth, changes in the rough endoplasmic reticulum and cell degeneration. The occurrence of damage in the digestive cells of the A. mellifera midgut indicates that spiromesifen does not cause mortality in honeybees, but its side-effects can damage the midgut, which may affect the longevity and behavior of this pollinator.

Exposure to chlorantraniliprole reduces locomotion, respiration, and causes histological changes in the midgut of velvetbean caterpillar Anticarsia gemmatalis (Lepidoptera: Noctuidae)

The anthranilic diamide, chlorantraniliprole is a systemic insecticide affecting ryanodine receptors. This insecticide is used to control caterpillars in soybean crops because it has low toxicity to non-target organisms. The objective was to identify side-effects of chlorantraniliprole on midgut histopathology, respiration and behavior of the velvetbean caterpillar Anticarsia gemmatalis in laboratoty. Chlorantraniliprole has LC50 = 0.61 (0.58-0.64) mg mL-1 for A. gemmatalis fourth instar caterpillars after 96 h. The insecticide causes severe histopathological effects in the midgut with epithelial disorganization, microvilli degeneration, cytoplasm vacuolization, cell fragmentation, and peritrophic matrix disorganization. The respiratory rate and the walking speed decrease, whereas the resting period increase for caterpillars exposed to this insecticide. Chlorantraniliprole is toxic to A. gemmatalis at median lethal concentrations causing severe histological and ultrastructural changes with degeneration of the midgut epithelium, reduction of respiratory rates and inducing an arresting behavioral response of this insect.

Respiration, predatory behavior and prey consumption by Podisus nigrispinus (Heteroptera: Pentatomidae) nymphs exposed to some insecticides

Podisus nigrispinus Dallas (Heteroptera: Pentatomidae) preys on insect pests in eucalyptus plantations where it can be exposed to insecticides used in pest control. The effect of insecticides on non-target natural enemies requires further study. The objective of the present study was to evaluate the side-effects of Bacillus thuringiensis (Bt), permethrin, tebufenozide and thiamethoxam on third instar nymphs of the predator P. nigrispinus in the laboratory. The toxicity of insecticides for this insect was determined by estimating their lethal concentrations. Podisus nigrispinus behavior after exposure to insecticides was analyzed using a video tracking system and the respiratory rate with a respirometer. Prey/nymph consumption was assessed after 24 h of starvation. The preference of P. nigrispinus nymphs, for prey treated or not with the insecticides, was evaluated in free choice tests. The insecticides Bt [LC₅₀ = 1.10(0.83-1.46) mg mL^-1], permethrin [LC₅₀ = 0.25(0.17-0.34) mg mL^-1], tebufenozide [LC₅₀ = 5.71(4.17-7.57) mg mL^-1] and thiamethoxam [LC₅₀ = 0.04(0.02-0.06) mg mL^-1] are toxic to P. nigrispinus nymphs. Bt and the insecticides tebufenozide, permethrin and thiamethoxam reduced the respiratory rate of P. nigrispinus. The insecticides permethrin, tebufenozide and thiamethoxam affect the locomotion of this insect's nymphs. Prey treated with Bt, permethrin and thiamethoxam are less preferred by P. nigrispinus. The survival of the nymphs of this predator was 93.3%, 66.7%, 56.6%, 0% and 0% in the control, tebufenozide, Bt, permethrin and thiamethoxam treatments, respectively. In addition, the reduction of prey consumption, treated with neurotoxic insecticides, reduces the predatory potential of this natural enemy. Bt and tefubenozide present low toxicity for P. nigrispinus, but the neurotoxic products have low compatibility with this natural enemy and, therefore, are not recommended, with this predator in the management of forest insect pests.

Low Doses of a Neonicotinoid Stimulate Reproduction in a Beneficial Predatory Insect

Biological stimulation induced by low doses of toxicants or other stressors is known as hormesis. Hormetic stimulation of life history traits in insect pests can negatively impact agriculture, but stimulation of beneficial insects could be leveraged to enhance biological control agents. We examined whether low doses of imidacloprid could enhance oviposition, fecundity, fertility, and survival in the beneficial stink bug predator, Podisus maculiventris (Say) (Hemiptera: Pentatomidae), exposed at different life stages and across two generations. When treated as young adults, P. maculiventris fecundity was stimulated at 0.5 and 1.0 mg/liter imidacloprid (<2% of the field rate) without changes in time to oviposition, fertility, and survival. Nymphs exposed to 0.015 mg/liter imidacloprid (<1% of the field rate) also had stimulated reproduction without effects on oviposition, fertility, and survival, but treatment of nymphs at 0.15 and 1.5 mg/liter imidacloprid stimulated fecundity at the expense of fertility and survival. In another experiment we found reproductive stimulation can occur trans-generationally without major reduction in fertility or survival. Our results suggest biocontrol producers may be able to strategically apply low doses of stress to natural enemies during culturing without compromising fitness in subsequent generations.

Combined toxicity of imidacloprid and cadmium on histopathology and acetylcholinesterase activity in aquatic oligochaetes (Tubifex tubifex Müller, 1774)

Imidacloprid is one of the neonicotinoid insecticides that has been applied in many farmlands and was detected in many water resources worldwide. However, not only this insecticide but also cadmium was found in the agricultural wastewater in close proximity to industrial areas. This research aims to investigate the acute toxicity of imidacloprid and cadmium on the biochemical changes, pathological changes and accumulation of cadmium in Tubifex tubifex after 24- and 48-h exposure. The results show that combined toxicity of two chemicals was synergistic. In combined toxicity test, cadmium accumulation and acetylcholinesterase activity in worm tissue were significantly increased when compared with the single test. The severity of histopathology shows a dose-dependent relationship. Epidermal and gut cell degeneration, hyperplasia of epidermal and gut cells, irregular surface of the epidermis, overexpression of chloragosome and nerve degeneration were observed. Overall, this research provides useful bio-markers to assess the toxicity of imidacloprid and cadmium on the aquatic environment.

Insights into the Toxicity and Degradation Mechanisms of Imidacloprid Via Physicochemical and Microbial Approaches

Imidacloprid is a neonicotinoid insecticide that has been widely used to control insect pests in agricultural fields for decades. It shows insecticidal activity mainly by blocking the normal conduction of the central nervous system in insects. However, in recent years, imidacloprid has been reported to be an emerging contaminant in all parts of the world, and has different toxic effects on a variety of non-target organisms, including human beings, due to its large-scale use. Hence, the removal of imidacloprid from the ecosystem has received widespread attention. Different remediation approaches have been studied to eliminate imidacloprid residues from the environment, such as oxidation, hydrolysis, adsorption, ultrasound, illumination, and biodegradation. In nature, microbial degradation is one of the most important processes controlling the fate of and transformation from imidacloprid use, and from an environmental point of view, it is the most promising means, as it is the most effective, least hazardous, and most environmentally friendly. To date, several imidacloprid-degrading microbes, including Bacillus, Pseudoxanthomonas, Mycobacterium, Rhizobium, Rhodococcus, and Stenotrophomonas, have been characterized for biodegradation. In addition, previous studies have found that many insects and microorganisms have developed resistance genes to and degradation enzymes of imidacloprid. Furthermore, the metabolites and degradation pathways of imidacloprid have been reported. However, reviews of the toxicity and degradation mechanisms of imidacloprid are rare. In this review, the toxicity and degradation mechanisms of imidacloprid are summarized in order to provide a theoretical and practical basis for the remediation of imidacloprid-contaminated environments.

The fungicide iprodione affects midgut cells of non-target honey bee Apis mellifera workers

The honey bee Apis mellifera is an important pollinator of agricultural crops and natural forests. Honey bee populations have declined over the years, as a result of diseases, pesticides, and management problems. Fungicides are the main pesticides found in pollen grains, which are the major source of protein for bees. The objective of this study was to evaluate the cytotoxic effects of the fungicide iprodione on midgut cells of adult A. mellifera workers. Bees were fed on iprodione (LD₅₀, determined by the manufacturer) for 12 or 24 h, and the midgut was examined using light and transmission electron microscopies. The expression level of the autophagy gene atg1 was assessed in midgut digestive cells. Cells of treated bees had signs of apoptosis: cytoplasmic vacuolization, apical cell protrusions, nuclear fragmentation, and chromatin condensation. Ultrastructural analysis revealed some cells undergoing autophagy and necrosis. Expression of atg1 was similar between treated and control bees, which can be explained by the facts that digestive cells had autolysosomes, whereas ATG-1 is found in the initial phases of autophagy. Iprodione acts by inhibiting the synthesis of glutathione, leading to the generation of reactive oxygen species, which in turn can induce different types of cell death. The results indicate that iprodione must be used with caution because it has side effects on non-target organisms, such as pollinator bees.

Histopathological and cytotoxic changes induced by spinosad on midgut cells of the non-target predator Podisus nigrispinus Dallas (Heteroptera: Pentatomidae)

Broad-spectrum insecticides used in pest control are a risk for non-target insects. Their compatibility to the insecticide spinosad, used in agriculture and forestry as a biological control tool, needs to be evaluated. Podisus nigrispinus Dallas (Heteroptera: Pentatomidae) is a predatory bug used in the pest management of agricultural and forest systems where spinosad is also frequently applied. The aim of this study was to evaluate the toxicity, histopathology and cytotoxicity in midgut cells of P. nigrispinus exposed to spinosad. The toxicity test was performed to determine the lethal concentrations of spinosad after exposure by ingestion. The histopathology and cytotoxicity caused by spinosad were analyzed in the three midgut regions (anterior, middle and posterior) of P. nigrispinus during different exposure periods. Spinosad, at low concentrations, was toxic to P. nigrispinus [LC₅₀ = 3.15 (3.02-3.26) μg.L^-1]. Cell degeneration features such as cytoplasm vacuolization, chromatin condensation and release of cell fragments to the midgut lumen were observed in this organ. Cell death via apoptosis was found in the three midgut regions of this predator after exposure to the insecticide. Spinosad is toxic to P. nigrispinus, and causes histological and cytological damage followed by cell death in the midgut, suggesting a dangerous effect on a beneficial non-target insect.

Bioactivity of the Cymbopogon citratus (Poaceae) essential oil and its terpenoid constituents on the predatory bug, Podisus nigrispinus (Heteroptera: Pentatomidae)

Podisus nigrispinus Dallas (Heteroptera: Pentatomidae), released in biological control programs, is a predator of Lepidopteran and Coleopteran species. Lemongrass essential oil and its constituents can be toxic to this natural enemy. The major constituents of lemongrass essential oil are neral (31.5%), citral (26.1%), and geranyl acetate (2.27%). Six concentrations of lemongrass essential oil and of its citral and geranyl acetate constituents were applied to the thorax of P. nigrispinus nymphs and adults. The walking and respiratory behavior of the P. nigrispinus third-instar nymphs, treated with citral and geranyl acetate at the LD50 and LD90 doses, were analyzed with video and respirometer. The lemongrass essential oil toxicity increased from first- to fifth-instar P. nigrispinus nymphs. The P. nigrispinus respiration rates (μL de CO2 h-1/insect) with citral and geranyl acetate in the LD50 and LD90 differed. Nymphs exposed to the lemongrass essential oil and its constituents on treated surfaces presented irritability or were repelled. Podisus nigrispinus adults were tolerant to the lemongrass essential oil and its constituents, geranyl acetate and citral. The altered respiratory activity with geranyl acetate and the fact that they were irritated and repelled by citral suggest caution with regard to the use of the lemongrass essential oil and its constituents in integrated pest management incorporating this predator, in order to avoid diminishing its efficiency against the pests.

Exposure to spinosad induces histopathological and cytotoxic effects on the salivary complex of the non-target predator Podisus nigrispinus

In integrated pest management systems, biological and chemical controls must be compatible. The insecticide spinosad affects some non-target insects and might compromise their fitness. The objective of this study was to evaluate the histopathological and cytotoxic effects of spinosad on the salivary complex of the predatory bug Podisus nigrispinus (Heteroptera: Pentatomidae). Spinosad toxicity and insect survival were determined using six concentrations of insecticide. Ultrastructural changes and cell death of salivary glands were analyzed after P. nigrispinus exposure to spinosad LC₅₀ (3.15 μg L^-1). The insecticide caused toxicity to P. nigrispinus; survival was 32% after 48 h of exposure to LC₅₀. The main histological changes in the salivary complex were disorganization of the epithelium, cytoplasmic vacuolization, and apocrine secretion into the gland lumen. Cytotoxic effects, such as release of granules and vacuoles into the lumen, presence of autophagosomes, enlargement of basal plasma membrane infoldings, and apoptosis, were observed. Spinosad causes toxicity, decreases survival, and changes the histology and cytology of the P. nigrispinus salivary complex. The results suggest that the cellular stress induced by the insecticide affects extra-oral digestion, compromising the potential of P. nigrispinus as a biological pest control agent.

Exposure to Insecticides Reduces Populations of Rhynchophorus palmarum in Oil Palm Plantations with Bud Rot Disease

The South American palm weevil (SAPW), Rhynchophorus palmarum Linnaeus (Coleoptera: Curculionidae) is the main pest of Elaeis guineensis and damages palm trees with bud rot disease in the Americas. The effects of six neurotoxic insecticides (abamectin, carbaryl, deltamethrin, fipronil, imidacloprid and spinosad) were evaluated against SAPW for toxicity, survival, reproduction, and mortality. Abamectin (LC₅₀ = 0.33 mg mL⁻¹), Carbaryl (LC₅₀ = 0.24 mg mL⁻¹), deltamethrin (LC₅₀ = 0.17 mg mL⁻¹), and fipronil (LC₅₀ = 0.42 mg mL⁻¹) were the most toxic to SAPW. Adult survival was 95% without exposure to insecticides, decreasing to 78–65% in insects treated with the LC₂₅ and 49–35% in insects exposed to LC₅₀. Sublethal doses of carbaryl, fipronil and imidacloprid showed significant effect on the reproduction of this insect. Mortality of SAPW populations caused by insecticides had similar effects in the laboratory and field conditions. The results suggest that carbaryl, deltamethrin, fipronil, and imidacloprid caused significantly higher mortality as compared to the control in SAPW and may be used to control its populations in oil palm trees where bud rot appears as the key disease for SAPW attraction and infestation.

Harmine induced apoptosis in Spodoptera frugiperda Sf9 cells by activating the endogenous apoptotic pathways and inhibiting DNA topoisomerase I activity

Harmine, a useful botanical compound, has demonstrated insecticidal activity against some pests. However, harmine's mechanism of action has not been thoroughly elucidated to date. To preliminarily explore harmine's insecticidal mechanisms, the cytotoxicity of harmine against Spodoptera frugiperda Sf9 cells was comprehensively investigated. Our results indicated that harmine induced apoptosis in Sf9 cells, as evidenced by cellular and nuclear morphological changes, DNA laddering and increases in caspase-3-like activities. In addition, activation of the mitochondrial apoptotic pathway by harmine was confirmed by the generation of ROS, opening of mitochondrial permeability transition pores (MPTPs), increase in cytosolic Ca²⁺, changes in mRNA expression levels of genes involved in the mitochondrial apoptotic pathway and increase and release of Cytochrome c. Furthermore, lysosomal membrane permeabilization, release of cathepsin L from the lysosome into the cytosol and cleavage of caspase-3 were also triggered, which indicated that lysosomes were involved in this physiological process. Moreover, the effect of harmine on DNA topoisomerase I activity was investigated by in vivo and molecular docking experiments. These data not only verified that harmine induced apoptosis via comprehensive activation of the mitochondrial and lysosomal pathways and inhibition of DNA topoisomerase I activity in Sf9 cells but also revealed a mechanism of harmine insecticidal functions for pest control.