Pyriproxyfen, a juvenile hormone analog, damages midgut cells and interferes with behaviors of Aedes aegypti larvae

Pyriproxyfen exposure compromises cocoon spinning and damages the Malpighian tubules of the nontarget predator Ceraeochrysa claveri (Neuroptera: Chrysopidae)

Pyriproxyfen has been extensively employed in the Neotropical region for agricultural pest management and insect vectors. However, measuring the sublethal and indirect effects of this active ingredient on nontarget organisms, such as lacewings, is important. Using morphological tools on target organs, we can evaluate these effects and use them as biomarkers for future ecotoxicological studies. Here, we investigated the effects of pyriproxyfen exposure on cocoon spinning and Malpighian tubules in Ceraeochrysa claveri adults. For this purpose, first-instar C. claveri larvae were orally exposed to Diatraea saccharalis egg clusters treated with pyriproxyfen in a solution of 50 or 100 mg a.i. L-1 throughout the larval stage. Insecticide exposure decreases predator survival, mainly in the prepupal and pupal stages, along with changes in the internal and external surfaces and thickness of the cocoon wall. Histopathological and ultrastructural injuries, including cytoplasmic vacuolization, loss of microvilli and a reduction in neutral glycoconjugates, were observed in Malphigian tubule cells of adults (≤24 h old). These changes indicate toxicological effects on Malpighian tubules that in lacewing involve cocoon spinning during metamorphosis and, in the adult stage, act in physiological processes of excretion and osmoregulation. Furthermore, it can affect the efficiency of the cocoon in protecting the specimen during metamorphosis against natural enemies and environmental factors. This organ has demonstrated its applicability as a biomarker for assessing the multisystemic effects of insecticides, thereby assisting in future risk assessments aimed at conserving nontargeted specimens.

Evaluation of developmental milestones and of brain measurements in rats exposed to the pesticide pyriproxyfen in prenatal period

Pyriproxyfen is a pesticide used in Brazil to control the Aedes aegypti mosquito, vector of arboviruses like Zika and dengue. However, this pesticide is structurally similar to retinoic acid, a metabolite of vitamin A that regulates neuronal differentiation and hindbrain development during the embryonic period. Due to the similarity between pyriproxyfen and retinoic acid, studies indicate that this pesticide may have cross-reactivity with retinoid receptors. Thus, pregnant exposure to pyriproxyfen could interfere in the nervous system development of the fetal. In this context, the present study evaluated whether prenatal exposure to pyriproxyfen affects neonatal development and brain structure in rats. Wistar rat pups were divided in three experimental groups: (1) negative control (CT-)-offspring of rats that drink potable water during pregnancy; (2) pyriproxyfen (PIR)-offspring of rats exposed to Sumilarv® prenatally, a pesticide that has pyriproxyfen as active ingredient; and (3) positive control (CT+)-offspring of rats exposed to an excess of vitamin A prenatally. Only vitamin A treated-pregnant showed lower weight gain, but gestation length was similar among pregnant that received potable water, water containing vitamin A and water containing Sumilarv. In relation to the offspring, PIR group exhibits a delayed front-limb suspension response but performed early the negative geotaxis reflex. On the other hand, CT+ group exhibited lower body weight in the 1st postnatal day, delayed audio startle response, but performed early the eyelids opening and hindlimb placing response. A reduction in the maximum brain width was observed both in PIR and CT+ groups, but a reduction in the number of neurons in the M1 cortex was showed only in CT+ group. The number of glial cells in this brain area was similar between the three experimental groups studied. Although prenatal exposure to pyriproxyfen did not alter neonatal milestones in the same way as vitamin A in excess, both substances caused a reduction in the maximum width of the brain, suggesting that this pesticide can produce neurotoxic effects during the embryonic period.

Sublethal exposure to thiamethoxam and pyraclostrobin affects the midgut and Malpighian tubules of the stingless bee Frieseomelitta varia (Hymenoptera: Apidae: Meliponini)

The stingless bee Frieseomelitta varia Lepeletier 1836 (Hymenoptera: Apidae) is an essential pollinator in natural and agricultural ecosystems in the Neotropical region. However, these bees may be exposed to pesticides during foraging, which can affect both individuals and their colonies. One example comes from the use of pyraclostrobin (a fungicide) and thiamethoxam (an insecticide) for pest control in pepper crops, which F. varia visits. This study aimed to evaluate the isolated and combined sublethal effects of thiamethoxam (TMX) (0.000543 ng a.i./µL) and pyraclostrobin (PYR) (1.5 ng i.a./µL) on the morphology of the midgut and Malpighian tubules of F. varia workers. Results showed that both pesticides, regardless of the exposure time (through feeding during 48 h or 96 h), disturbed the morphology of the analyzed organs. Specifically, F. varia exposed orally to sublethal concentrations of thiamethoxam and pyraclostrobin, either alone or in combination, exhibited a higher rate of damage to the midgut (e.g., vacuolization, apocrine secretion, and cellular elimination) compared to the bees in the control groups, both after 48 h and 96 h of exposure. In Malpighian tubules, vacuolation is the only damage present. As the observed morphological alterations likely compromise the excretion and absorption functions, exposure to pyraclostrobin and thiamethoxam may lead to disturbances at both the individual and colony levels. These results highlight the urgent need for a future reassessment of the safety of fungicides and insecticides regarding their potential effects on bee populations.

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.

Exploring the effects of the acaricide cyflumetofen on the vital organs of the honey bee Apis mellifera (Hymenoptera: Apidae) workers

Bees are important for maintaining ecosystems, pollinating crops and producing marketable products. In recent years, a decline in bee populations has been reported, with multifactorial causes, including the intensification of pesticide use in agriculture. Among pesticides, cyflumetofen is an insecticide and acaricide used in apple, coffee and citrus crops, whose main pollinator is the honey bee Apis mellifera. Therefore, this bee is a potential target of cyflumetofen during foraging. This study evaluated the histopathological and cytological damage in the midgut, hypopharyngeal glands and fat body of A. mellifera workers exposed to LC50 of cyflumetofen. The midgut epithelium of exposed bees presented cytoplasmic vacuolization, release of vesicles and cell fragments, which indicate autophagy, increased production of digestive enzymes and cell death, respectively. The cytological analysis of the midgut revealed the dilation of the basal labyrinth and the presence of spherocrystals in the digestive cells. The hypopharyngeal glands produced greater amounts of secretion in treated bees, whereas no changes were observed in the fat body. The results indicate that acute exposure to cyflumetofen negatively affect A. mellifera, causing damage to the midgut and changes in the hypopharyngeal glands, which may compromise the survival and foraging of this pollinator.

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.

Photoactivated 9-methylacridine destroys midgut tissues of Aedes aegypti larvae by targeting ROS-mediated apoptosis in the mitochondrial pathway of midgut cells

An aromatic ring-containing compound with a wide range of biological activities, 9-methylacridine (AD-9-Me) is a precursor for the synthesis of various drugs. However, its photoactivation properties and mechanism of damage as a photo activator against Aedes aegypti are unknown. The toxic effects of AD-9-Me on Aedes aegypti mosquitoes were determined under light and non-light conditions. The results showed that the toxicity of AD-9-Me to mosquito larvae was significantly higher than that of the dark treatment after 24 h of light exposure; AD-9-Me was mainly distributed in the midgut of larvae, after 24 h of treatment, it can cause an increase in calcium ion concentration, reactive oxygen species (ROS) eruption and ROS accumulation by blocking the ROS elimination pathway in midgut cells. This in turn caused an increase in protein carbonyl and malondialdehyde (MDA) content, a decrease in mitochondrial membrane potential (MMP), a disruption of the barrier function of midgut tissues, a significant decrease in midgut weight and chitin content, which induced the up-regulation of AeDronc, AeCaspase8 and AeCaspase7 genes, leading to apoptotic cell death. In this study, we confirmed that AD-9-Me has photoactivation activity and mainly acts on the midgut of mosquito larvae, which can generate a large amount of ROS in the cells of the midgut and induce apoptosis to occur, resulting in the disruption of the function of the tissues of mosquito larvae, accelerating the death and delaying the development of the mosquito larvae.

Accelerating sexual maturation of male Anastrepha ludens (Diptera: Tephritidae) fruit flies by adding two juvenile hormone analogues

BACKGROUND

Improving the mating competitiveness and survival of sterile males are direct means to increase the effectiveness of the sterile insect technique (SIT). Some insecticide growth regulators, such as the juvenile hormone analogue (JHA) methoprene, have been used to improve the mating competitiveness of male tephritid flies by reducing their sexual maturation period. However, the application of methoprene reduces fly resistance to stress and decreases survival. Here, we compared the effects of methoprene and pyriproxyfen (PPF), another JHA, in Anastrepha ludens males. PPF is an insect growth regulator that exhibits higher negative effects on the larval molting process than methoprene or natural juvenile hormone. Both compounds were administered at two doses (0.05% and 0.10%) via the male diet immediately after emergence.

RESULTS

Our results show that both PPF and methoprene reduced male sexual maturation. However, PPF-treated males exhibited a shorter maturation period and obtained more matings at a given age than methoprene-treated males. No significant differences were observed between the two PPF doses tested (0.05% and 0.10%). Male survival was equally reduced by the two compounds.

CONCLUSION

Our results demonstrate that PPF accelerated sexual development without reducing the mating propensity of sterile male flies and can be used as a suitable alternative for methoprene. © 2023 Society of Chemical Industry.

The promoting effects of pyriproxyfen on autophagy and apoptosis in silk glands of non-target insect silkworm, Bombyx mori

Pyriproxyfen is a juvenile hormone analogue. The physiological effects of its low-concentration drift during the process of controlling agricultural and forestry pests on non-target organisms in the ecological environment are unpredictable, especially the effects on organs that play a key role in biological function are worthy of attention. The silk gland is an important organ for silk-secreting insects. Herein, we studied the effects of trace pyriproxyfen on autophagy and apoptosis of the silk gland in the lepidopteran model insect, Bombyx mori (silkworm). After treating fifth instar silkworm larvae with pyriproxyfen for 24 h, we found significant shrinkage, vacuolization, and fragmentation in the posterior silk gland (PSG). In addition, the results of autophagy-related genes of ATG8 and TUNEL assay also demonstrated that autophagy and apoptosis in the PSG of the silkworm was induced by pyriproxyfen. RNA-Seq results showed that pyriproxyfen treatment resulted in the activation of juvenile hormone signaling pathway genes and inhibition of 20-hydroxyecdysone (20E) signaling pathway genes. Among the 1808 significantly differentially expressed genes, 796 were upregulated and 1012 were downregulated. Among them, 30 genes were identified for autophagy-related signaling pathways, such as NOD-like receptor signaling pathway and mTOR signaling pathway, and 30 genes were identified for apoptosis-related signaling pathways, such as P53 signaling pathway and TNF signaling pathway. Further qRT-PCR and in vitro gland culture studies showed that the autophagy-related genes Atg5, Atg6, Atg12, Atg16 and the apoptosis-related genes Aif, Dronc, Dredd, and Caspase1 were responsive to the treatment of pyriproxyfen, with transcription levels up-regulated from 24 to 72 h. In addition, ATG5, ATG6, and Dronc genes had a more direct response to pyriproxyfen treatment. These results suggested that pyriproxyfen treatment could disrupt the hormone regulation in silkworms, promoting autophagy and apoptosis in the PSG. This study provides more evidence for the research on the damage of juvenile hormone analogues to non-target organisms or organs in the environment, and provides reference information for the scientific and rational use of juvenile hormone pesticides.

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.

Effects of lufenuron treatments on the growth and development of Spodoptera frugiperda (Lepidoptera: Noctuidae)

Lufenuron is an effective benzoylurea insecticide that inhibits the synthesis of chitin and regulates the growth of insects. However, little is known about the effects of lufenuron treatment on the development of Spodoptera frugiperda (J. E. Smith). In this study, we assessed the toxicity of lufenuron on S. frugiperda and evaluated the effects of lufenuron treatment on the growth and development of S. frugiperda. The results showed that lufenuron exhibits high insecticidal activity against S. frugiperda, with the LC₅₀ value of 0.99 mg L^-1. Lufenuron treatments can significantly prolong the larval developmental duration and reduce the rates of pupation and emergence. To further explore the underlying mechanism of this observation, the expression profiles of the chitin synthase gene (SfCHS) and chitinase gene (SfCHT), two key enzyme genes involved in the molting of S. frugiperda, were determined after exposure to lufenuron for 96 h. The results of qRT-PCR demonstrated that lufenuron treatments can significantly reduce the expression of SfCHT, while the expression of SfCHS remained relatively stable. Furthermore, we found that lufenuron strongly interacted with chitinase (SfCHT) (-10.8 kcal/mol) and chitin synthase (SfCHS) (R1: -9.7 kcal/mol; R2: -10.2 kcal/mol). Our results indicated that lufenuron has significant effects on the development of S. frugiperda that might be attributed to the differential expression of SfCHT and SfCHS.

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.

Midgut and fat body: Multisystemic action of pyriproxyfen on non-target organism Ceraeochrysa claveri (Neuroptera: Chrysopidae)

Morphological tools can assist in the evaluation of effects of insecticides on non-target insects. Pyriproxyfen, a juvenile hormone analog, is known to interfere with growth and metamorphosis of insects. However, there are studies showing indirect effects on natural enemies, including green lacewings. Few prior studies describe morphological effects of pyriproxyfen on target insect organs, especially on natural enemies. Through morphological tools, this study aimed to characterize the midgut and fat body, both important organs of digestion and great metabolic activity respectively, of the predator Ceraeochrysa claveri after chronic exposure to pyriproxyfen. Larvae of C. claveri were fed Diatraea saccharalis egg clusters treated with pyriproxyfen in solution of 50 or 100 mg a.i. L^-1 throughout the larval stage. The biological data revealed significant increases in development time, especially in the third instar, and in cumulative mortality from the prepupal into the pupal stage. Morphological analysis of adult midgut (≤24 h old) showed damage including formation of epithelial folds, intercellular spaces, emission of cytoplasmic protrusions. Both fat body regions presented decrease of lipid droplets, vacuolization of trophocytes and mitochondrial injury featuring a multisystemic action. In both organs, pyriproxyfen exposure induced significant oxidative stress by mitochondrial superoxide production. Cytoprotective responses were induced in midgut and fat body cells by augmenting the number of cytoplasmic granules containing calcium and expression of HSP 90. Both organs proved to be efficient in presenting histopathological alterations, showing the sensitivity and applicability of this morphological tool for evaluating other insecticides in non-target organisms.

The JH-Met2-Kr-h1 pathway is involved in pyriproxyfen-induced defects of metamorphosis and silk protein synthesis in silkworms, Bombyx mori

Environmental residues of pryriproxyfen, a juvenile hormone analogue (JHA) type pesticide, may have on unintended consequences on non-target insects. However, the mechanism of pyriproxyfen action and silk protein synthesis in silkworms has not been reported. In the present study, we treated the silkworms with trace pyriproxyfen (1 × 10^-4 mg/L) and found that the silkworm larvae showed no obvious poisoning symptoms, while the development of silk glands and cocoon-forming function were both seriously damaged due to the accumulation of pyriproxyfen in posterior silk gland (PSG). The titer of the juvenile hormone (JH) was increased, whereas the content of 20-hydroxyecdysone (20E) was reduced in pyriproxyfen-exposed hemolymph. Met2 is a component of the JH receptor complex and JH can promote its phosphorylation. We found Met2 and SRC were up-regulated in the larval stage after pyriproxyfen exposure, the JH-Met2/SRC complex led to the up-regulation of downstream genes Kr-h1, and Dimm, and then specifically inhibited the transcription of Fib-H. Meanwhile, the transcription of ecdysone inducible transcription factor Br-C Z4 was also inhibited by pyriproxyfen and resulted in the defects of metamorphosis. In conclusion, the trace pyriproxyfen could affect the metamorphosis and silk protein synthesis through the Met2-mediated pathway. Our study provided new evidence that Met2 might be a potential target gene of JHA in Lepidoptera.

Juvenile hormone analog enhances Zika virus infection in Aedes aegypti

In recent years, there has been a rise in the emergence of arboviruses of public health importance, including Zika, chikungunya, dengue, and yellow fever viruses. Insecticide-based mosquito control has been the primary method for mitigating transmission of arboviruses. The consequences for the application of insecticides include both lethal and sublethal effects, and associated development of insecticide resistance. However, little is known about the influence on arboviral transmission. Mosquitoes with phenotypes that exhibit insecticide resistance or experience sublethal effects may be associated with altered susceptibility to arbovirus infection and transmission. Juvenile hormone analogs (JHAs) are insecticides that prevent pupa to adult molting of mosquitoes by mimicking the action of their natural juvenile hormone. Here, we examined whether the JHA pyriproxyfen interacts with ambient temperature (20 °C and 30 °C) during juvenile stages to influence life-history traits, population growth (λ'), and Zika virus (ZIKV) infection in Aedes aegypti. Development time of females was lengthened at 20 °C and in the presence of JHA. Prevention of pupa to adult molting by JHA was differentially higher at elevated temperature than low temperature. Size of females was larger at 20 °C and smaller at 30 °C. Infection, disseminated infection, and transmission of ZIKV in females were enhanced by JHA at both 20 °C and 30 °C relative to the controls. These results demonstrate that mosquito life-history and vector competence parameters are strongly influenced by interactive effects of JHA and temperature. The JHA-induced enhancement of ZIKV infection in females should be a consideration when implementing JHA in vector control strategies.

Evaluation of a mosquito home system for controlling Aedes aegypti

BACKGROUND

Dengue is a significant public health issue that is caused by Aedes spp. mosquitoes. The current vector control methods are unable to effectively reduce Aedes populations and thus fail to decrease dengue transmission. Hence, there is an urgent need for new tools and strategies to reduce dengue transmission in a wide range of settings. In this study, the Mosquito Home System (MHS) and Mosquito Home Aqua (MHAQ) formulations were assessed as commercial autodissemination traps in laboratory and small-scale field trials.

METHOD

Multiple series of laboratory and small-scale field trials were performed to assess the efficacy of MHS and MHAQ exposed to Ae. aegypti. In the laboratory trials, various parameters such as fecundity, fertility, wing size, oviposition preferences, residual effects, and MHAQ transference to other containers through controlled experiments were tested. For small-scale field trials, the efficacy of the MHS and MHAQ approaches was determined to ascertain whether wild mosquitoes could transfer the MHAQ formulation from MHS stations to ovitraps.

RESULTS

The data revealed that Ae. aegypti was highly susceptible to low concentrations of MHAQ formulations and had a residual effect of up to 3 months, with MHAQ exposure affecting fecundity, fertility, and mosquito wing size. In the oviposition studies, gravid females strongly preferred the hay infusion compared to tap water and MHAQ during egg-laying in the laboratory. Nevertheless, the use of commercial MHAQ by MHS was highly attractive in field settings compared to conventional ovitraps among local Aedes spp. mosquitoes. In addition, MHAQ horizontal transfer activities in the laboratory and small-scale field trials were demonstrated through larval bioassays. These findings demonstrated the potential of MHAQ to be transferred to new containers in each study site.

CONCLUSION

This study provided proof of principle for the autodissemination of MHAQ. Through further refinement, this technique and device could become an effective oviposition trap and offer an alternative preventive tool for vector control management.

In Silico Prediction of the Mechanism of Action of Pyriproxyfen and 4'-OH-Pyriproxyfen against A. mellifera and H. sapiens Receptors

Background. Poisoning from pesticides can be extremely hazardous for non-invasive species, such as bees, and humans causing nearly 300,000 deaths worldwide every year. Several pesticides are recognized as endocrine disruptors compounds that alter the production of the normal hormones mainly by acting through their interaction with nuclear receptors (NRs). Among the insecticides, one of the most used is pyriproxyfen. As analogous to the juvenile hormone, the pyriproxyfen acts in the bee’s larval growth and creates malformations at the adult organism level. Methods. This work aims to investigate the possible negative effects of pyriproxyfen and its metabolite, the 4′-OH-pyriproxyfen, on human and bee health. We particularly investigated the mechanism of binding of pyriproxyfen and its metabolite with ultraspiracle protein/ecdysone receptor (USP-EcR) dimer of A. mellifera and the relative heterodimer farnesoid X receptor/retinoid X receptor alpha (FXR-RXRα) of H. sapiens using molecular dynamic simulations. Results. The results revealed that pyriproxyfen and its metabolite, the 4′-OH- pyriproxyfen, stabilize each dimer and resulted in stronger binders than the natural ligands. Conclusion. We demonstrated the endocrine interference of two pesticides and explained their possible mechanism of action. Furthermore, in vitro studies should be carried out to evaluate the biological effects of pyriproxyfen and its metabolite.

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.

Methoxyfenozide, a Molting Hormone Agonist, Affects Autogeny Capacity, Oviposition, Fecundity, and Fertility in Culex pipiens (Diptera: Culicidae)

The current study aimed to evaluate the effects of methoxyfenozide (RH-2485), an insect growth disrupter (IGD) belonging to molting hormone agonist class, against female adults of Culex pipiens L. under laboratory conditions. Lethal concentrations (LC50 = 24.54 µg/liter and LC90 = 70.79 µg/liter), previously determined against fourth instar larvae, were tested for adult female fertility, fecundity and oviposition after tarsal contact before mating and any bloodmeal. Methoxyfenozide was found to alter negatively their autogeny capacity and oviposition. A strong reduction of 56% and 72% (P < 0.001) in females' autogeny capacity was observed in both treated series, respectively. Alteration in oviposition were found to be higher with LC90 (OAI-LC90 = -0.62) than with the LC50 (OAI-LC50 = -0.42). Also fecundity and hatching rate (fertility) were significantly reduced in treated series as compared to controls. A significant reduction of 37.65 and 28.23% in fecundity and decrease of 56.85 and 71.87% in fertility were found, respectively in LC50 and LC90 treated series. Obtained data clearly demonstrated that methoxyfenozide have significant depressive effect on reproductive potential against medically important vector with minimizing ecotoxicological risks in mosquitoes management.

Pyriproxyfen induces lethal and sublethal effects on biological traits and demographic growth parameters in Musca domestica

Musca domestica is a global insect-pest of human beings and animal agriculture. Pyriproxyfen, a juvenile hormone analog, has shown its potential for effective management of M. domestica. However, lethal and sublethal effects of pyriproxyfen on biological traits and demographic growth parameters of M. domestica are still unknown. The present study investigated the effects of lethal and sublethal concentrations on different biological traits of M. domestica for two generations i.e., exposed parents (F0) and their offspring (F1). Concentration-response bioassays revealed that concentrations of pyriproxyfen that caused 50% (LC₅₀), 25% (LC₂₅), 10% (LC₁₀) and 2% (LC₂) mortality of M. domestica were estimated as 0.12, 0.06, 0.03 and 0.01 μg/g, respectively. In the F0 generation, exposure of 3^rd instar larvae to these concentrations resulted in a reduced pupation rate, lengthened pupal stage duration, light weight pupae and reduction in adult emergence in a concentration-dependent manner. In the case of F1 generation, similar trend was observed for pupation rate, pupal stage duration, and total developmental period (i.e., egg to adult); however, pupal weight was affected at LC₁₀, LC₂₅, LC₅₀ levels, and adult emergence at only LC₂₅ and LC₅₀ levels. The values of demographic growth parameters, analyzed through age-stage, two-sex life table theory, were significantly decreased at all the levels of pyriproxyfen compared with control. This study highlights that pyriproxyfen has the potential to suppress the population of M. domestica through its lethal and sublethal effects and presents an empirical basis from which to consider management decisions for chemical control in the field.

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.

The effects of exposure to pyriproxyfen and predation on Zika virus infection and transmission in Aedes aegypti

Zika virus (ZIKV) is an emerging mosquito-borne pathogen that can cause global public health threats. In the absence of effective antiviral medications, prevention measures rely largely on reducing the number of adult mosquito vectors by targeting juvenile stages. Despite the importance of juvenile mosquito control measures in reducing adult population size, a full understanding of the effects of these measures in determining mosquito phenotypic traits and in mosquito-arbovirus interactions is poorly understood. Pyriproxyfen is a juvenile hormone analog that primarily blocks adult emergence, but does not cause mortality in larvae. This mechanism has the potential to work in combination with other juvenile sources of mortality in nature such as predation to affect mosquito populations. Here, we experimentally evaluated the effects of juvenile exposure to pyriproxyfen and predatory mosquito Toxorhynchites rutilus on Aedes aegypti phenotypes including susceptibility to ZIKV infection and transmission. We discovered that combined effects of pyriproxyfen and Tx. rutilus led to higher inhibition of adult emergence in Ae. aegypti than observed in pyriproxyfen or Tx. rutilus treatments alone. Adult body size was larger in treatments containing Tx. rutilus and in treatments mimicking the daily mortality of predation compared to control or pyriproxyfen treatments. Susceptibility to infection with ZIKV in Ae. aegypti was reduced in predator treatment relative to those exposed to pyriproxyfen. Disseminated infection, transmission, and titers of ZIKV in Ae. aegypti were similar in all treatments relative to controls. Our data suggest that the combination of pyriproxyfen and Tx. rutilus can inhibit adult Ae. aegypti emergence but may confer a fitness advantage in survivors and does not inhibit their vector competence for ZIKV relative to controls. Understanding the ultimate consequences of juvenile mosquito control measures on subsequent adults’ ability to transmit pathogens is critical to fully understand their overall impacts.

Mosquito control approaches primarily depend on lowering the number of potential adult mosquito vectors by inhibiting juvenile stages to reduce the risk of pathogen transmission. Pyriproxyfen is a juvenile hormone analog that inhibits the emergence of adult mosquitoes by interrupting metamorphosis, but does not target larvae. This mechanism allows natural sources of mortality like predation to act in combination with pyriproxyfen to affect mosquito population size. Here, we determined the effects of juvenile exposure to pyriproxyfen and predatory mosquito Toxorhynchites rutilus on adult Aedes aegypti traits, including infection with Zika virus. Combined effects of pyriproxyfen and Tx. rutilus led to strong inhibition of adult emergence in Ae. aegypti. Treatments containing predators or those mimicking the daily mortality of predation produced larger sized adults. Susceptibility to ZIKV infection was lowest in the predator treatment and highest in the pyriproxyfen treatment. Disseminated infection, transmission, and viral titers of ZIKV were similar between treatments. Our data suggest that the combination of pyriproxyfen and predators can enhance inhibition of adult Ae. aegypti emergence, but survivors may have fitness benefits such being larger mosquitoes. Understanding the consequences of control approaches in mosquito-pathogen interactions will assist to evaluate their suitability in mosquito control programs.

Acute Toxicity and Sublethal Effects of Lemongrass Essential Oil and Their Components against the Granary Weevil, Sitophilus granarius

In the present work, we evaluate the toxic and repellent properties of lemongrass (Cymbopogon citratus (DC. ex Nees) Stapf.) essential oil and its components against Sitophilus granarius Linnaeus as an alternative to insecticide use. The lethal dose (LD50 and LD90), survivorship, respiration rate, and repellency on adults of S. granarius exposed to different doses of lemongrass oil and some of its components were evaluated. The chemical composition of the essential oil was found to have the major components of neral (24.6%), citral (18.7%), geranyl acetate (12.4%), geranial (12.3%), and limonene (7.55%). Lemongrass essential oil (LD50 = 4.03 µg·insect-1), citral (LD50 = 6.92 µg·insect-1), and geranyl acetate (LD50 = 3.93 µg·insect-1) were toxic to S. granarius adults. Survivorship was 99.9% in insects not exposed to lemongrass essential oil, decreasing to 57.6%, 43.1%, and 25.9% in insects exposed to LD50 of essential oil, citral, and geranyl acetate, respectively. The insects had low respiratory rates and locomotion after exposure to the essential oil, geranyl acetate, and citral. Our data show that lemongrass essential oils and their components have insecticidal and repellent activity against S. granarius and, therefore, have the potential for application in stored grain pest management schemes.