Programmed Cell Death in the Honey Bee (Apis mellifera) (Hymenoptera: Apidae) Worker Brain Induced by Imidacloprid

Multiple stresses induced by chronic exposure to flupyradifurone affect honey bee physiological states

Flupyradifurone (FPF) has been reported to have a potential risk to terrestrial and aquatic ecosystems. In the present study, the effects of chronic FPF exposure on bees were systematically investigated at the individual behavioral, tissue, cell, enzyme activity, and the gene expression levels. Chronic exposure (14 d) to FPF led to reduced survival (12 mg/L), body weight gain (4 and 12 mg/L), and food utilization efficiency (4 and 12 mg/L). Additionally, FPF exposure (12 mg/L) impaired sucrose sensitivity and memory of bees. Morphological analysis revealed significant cellular and subcellular changes in brain neurons and midgut epithelial cells, including mitochondrial damage, nuclear disintegration, and apoptosis. FPF exposure (4 and 12 mg/L) led to oxidative stress, as evidenced by increased lipid peroxidation and alterations in antioxidant enzyme activity. Notably, gene expression analysis indicated significant dysregulation of apoptosis, immune, detoxification, sucrose responsiveness and memory-related genes, suggesting the involvement of different pathways in FPF-induced toxicity. The multiple stresses and potential mechanisms described here provide a basis for determining the intrinsic toxicity of FPF.

The protective role of L-carnitine on oxidative stress, neurotransmitter perturbations, astrogliosis, and apoptosis induced by thiamethoxam in the brains of male rats

Synthetic organic insecticides such as pyrethroids, organophosphates, neonicotinoids, and others have the potential to disrupt ecosystems and are often toxic to humans. Thiamethoxam (TMX), a neonicotinoid insecticide , is a widely used insecticide with neurotoxic potential. L-Carnitine (LC) is regarded as the "gatekeeper" in charge of allowing long-chain fatty acids into cell mitochondria. LC is an endogenous chemical that is renowned for its prospective biological activity in addition to its role in energy metabolism. This study investigated the protective effects of LC against TMX-induced neurotoxicity in male Wistar rats. For 28 days, animals were divided into four groups and treated daily with either LC (300 mg/kg), TMX (100 mg/kg), or both at the aforementioned doses. Our results revealed marked serum lipid profile and electrolyte changes, declines in brain antioxidants and neurotransmitters (acetylcholine, dopamine, and serotonin levels) with elevations in thiobarbituric acid reactive substances and proinflammatory cytokine levels, as well as acetylcholinesterase and monoamine oxidase brain activity in TMX-treated rats. TMX also increased the expression of caspase-3 and glial fibrillary acidic protein. In contrast, pretreatment with LC attenuated TMX-induced brain injury by suppressing oxidative stress and proinflammatory cytokines and modulating neurotransmitter levels. It also ameliorated the expression of apoptotic and astrogliosis markers. It could be concluded that LC has antioxidant, anti-inflammatory, anti-astrogliosis, and anti-apoptotic potential against TMX neurotoxicity.

Early-Life Sublethal Thiacloprid Exposure to Honey Bee Larvae: Enduring Effects on Adult Bee Cognitive Abilities

Honey bees have significant ecological and economic value as important pollinators, but they are continuously exposed to various environmental stressors, including insecticides, which can impair their health and cause colony decline. (1) Background: Cognitive abilities are vital for the functional maintenance of honey bees; however, it remains unknown if chronic, low-dose exposure to thiacloprid during the larval stage impairs the cognitive abilities of emerged adult honey bees. (2) Methods: To explore this question, honey bee larvae were fed 0, 0.5, and 1.0 mg/L thiacloprid during their developmental phase. Then, the cognitive (i.e., olfactory learning and memory) abilities of adult honey bees were quantified to assess the delayed impacts of early-stage thiacloprid exposure on adult honey bee cognition. Neural apoptosis and transcriptomic level were also evaluated to explore the neurological mechanisms underlying these effects. (3) Results: Our results revealed that chronic larval exposure to sublethal thiacloprid impaired the learning and memory abilities of adult honey bees by inducing neuronal apoptosis and transcriptomic alterations. (4) Conclusions: We highlighted a previously unknown impairment caused by thiacloprid in honey bees.

Imidacloprid Induces Lysosomal Dysfunction and Cell Death in Human Astrocytes and Fibroblasts-Environmental Implication of a Clinical Case Report

Imidacloprid (IMI), a neonicotinoid insecticide, has potential cytotoxic and genotoxic effects on human and experimental models, respectively. While being an emerging environmental contaminant, occupational exposure and related cellular mechanisms are unknown. Herein, we were motivated by a specific patient case where occupational exposure to an IMI-containing plant protection product was associated with the diagnosis of Bell's palsy. The aim was to investigate the toxic effects and cellular mechanisms of IMI exposure on glial cells (D384 human astrocytes) and on human fibroblasts (AG01518). IMI-treated astrocytes showed a reduction in cell number and dose-dependent cytotoxicity at 24 h. Lower doses of IMI induced reactive oxygen species (ROS) and lysosomal membrane permeabilisation (LMP), causing apoptosis and autophagic dysfunction, while high doses caused significant necrotic cell death. Using normal fibroblasts, we found that IMI-induced autophagic dysfunction and lysosomal damage, activated lysophagy, and resulted in a compensatory increase in lysosomes. In conclusion, the observed IMI-induced effects on human glial cells and fibroblasts provide a possible link between IMI cytotoxicity and neurological complications observed clinically in the patient exposed to this neonicotinoid insecticide.

Ame-miR-980-3p participates in autophagy-mediated midgut remodelling in Apis mellifera via targeting Atg2B

Autophagy is a process that serves to degrade damaged proteins and organelles, thereby promoting cell homeostasis, differentiation, development and survival. Many miRNAs have been found to have regulatory roles in autophagy. In insects, it has been shown that autophagy is involved in hormone-regulated programmed cell death during metamorphic midgut remodelling. However, whether this is also true during the remodelling of the honey bee midgut is unclear. In the present study, we explored the relationship between autophagy and midgut remodelling and sought to identify miRNAs involved in this physiological process. We found that autophagy occurred during midgut remodelling and that the inhibition of autophagy resulted in midgut dysplasia in prepupae. Differentially expressed miRNAs enriched in the autophagy signalling pathway during midgut remodelling were identified by small RNA-seq. Ame-miR-980-3p, which targets the autophagy-related gene Atg2B, was screened out. Furthermore, abnormal expression of ame-miR-980-3p in the pupal stage led to the thinning of the midgut wall of newly emerged bees (NE). When ame-miR-980-3p expression was inhibited, the intestinal villi of NE bees became significantly shorter and sparse, and the lipid signal in the peritrophic matrix of Pb almost disappeared, indicating that the adult midgut was underdeveloped and the lipid absorption ability was weakened. Taken together, ame-miR-980-3p targeted Atg2B to participate in the regulation of midgut autophagy in the pupae, and the abnormal expression of ame-miR-980-3p would interfere with cell proliferation and death in the process of midgut remodelling, hinder the formation of adult midgut and eventually lead to adult midgut dysplasia and affect the lipid absorption function of the midgut in Apis mellifera.

Effects of thiamethoxam on brain structure of Bombus terrestris (Hymenoptera: Apidae) workers

Neonicotinoids are the most widely used pesticide compared to other major insecticide classes known worldwide and have the fastest growing market share. Many studies showed that neonicotinoid pesticides harm honeybee learning and farming activities, negatively affect colony adaptation and reduce pollination abilities. Bumblebees are heavily preferred species all over the world in order to ensure pollination in plant production. In this study, sublethal effects of the neonicotinoid insecticide thiamethoxam on the brain of Bombus terrestris workers were analyzed. Suspensions (1/1000, 1/100, 1/10) of the maximum recommended dose of thiamethoxam were applied to the workers. 48 h after spraying, morphological effects on the brains of workers were studied. According to area measurements of ICC's of Kenyon cells, there was a significant difference between 1/10 dose and all groups. On the other hand, areas of INC's of Kenyon cells showed a significant difference between the control group and all dose groups. Neuropil disorganization in the calyces increased gradually and differed significantly between the groups and was mostly detected at the highest dose (1/10). Apart from optic lobes, pycnotic nuclei were also observed in the middle region of calyces of mushroom bodies in the high dose group. Also, the width of the lamina, medulla and lobula parts of the optic lobes of each group and the areas of the antennal lobes were measured and significant differences were determined between the groups. The results of the study revealed that sublethal doses of thiamethoxam caused some negative impacts on brain morphology of B. terrestris workers.

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.

Honey bee larval culture in vitro: gut emptying determines the transition from larva to prepupa and recombinant AccApidaecin improves antibacterial activity

In vitro rearing of honey bee larvae is ideal for bioassay studies; no honey bee stable cell lines are available. Inconsistency of internal development staging of reared larvae and a susceptibility to contamination are common problems encountered. Standardized protocols on rearing larvae in vitro to make the larvae growth and development more similar to that of natural colonies are necessary to ensure the accuracy of experimental results and promote honey bee research as a model organism. Here, we concluded that when larval fasting weight was >160 mg, the time point of gut emptying can be defined as the critical point separating the larval and prepupal stages. In this way, we can conduct precise studies on the prepupal stage, such as organ remodeling during metamorphosis. Simultaneously, we further verified that recombinant AccApidaecin in genetic engineered bacteria added to the larval diet upregulated antibacterial peptide gene expression, and did not stimulate the stress response in larvae, nor did it affect the pupation rate or eclosion rate. This demonstrated that feeding recombinant AccApidaecin can enhance the individual antibacterial ability at the molecular level.

Bioinsecticide spinosad poses multiple harmful effects on foragers of Apis mellifera

There are multifactorial causes for the recent decline in bee populations, which has resulted in compromised pollination and reduced biodiversity. Bees are considered one of the most important non-target insects affected by insecticides used in crop production. In the present study, we investigated the effects of acute oral exposure to spinosad on the survival, food consumption, flight behavior, respiration rate, activity of detoxification enzymes, total antioxidant capacity (TAC), brain morphology, and hemocyte count of Apis mellifera foragers. We tested six different concentrations of spinosad for the first two analyses, followed by LC₅₀ (7.7 mg L^-1) for other assays. Spinosad ingestion decreased survival and food consumption. Exposure to spinosad LC₅₀ reduced flight capacity, respiration rate, and superoxide dismutase activity. Furthermore, this concentration increased glutathione S-transferase activity and the TAC of the brain. Notably, exposure to LC₅₀ damaged mushroom bodies, reduced the total hemocyte count and granulocyte number, and increased the number of prohemocytes. These findings imply that the neurotoxin spinosad affects various crucial functions and tissues important for bee performance and that the toxic effects are complex and detrimental to individual homeostasis.

Mixture toxic effects of thiacloprid and cyproconazole on honey bees (Apis mellifera L.)

Pesticide exposure remains one of the main factors in the population decline of insect pollinators. It is urgently necessary to assess the effects of mixtures on pollinator risk assessments because they are often exposed to numerous agrochemicals. In the present study, we explored the mixture toxic effects of thiacloprid (THI) and cyproconazole (CYP) on honey bees (Apis mellifera L.). Our findings revealed that THI possessed higher acute toxicity to A. mellifera (96-h LC₅₀ value of 216.3 mg a.i. L^-1) than CYP (96-h LC₅₀ value of 601.4 mg a.i. L^-1). It's worth noting that the mixture of THI and CYP exerted an acute synergistic effect on honey bees. At the same time, the activities of detoxification enzyme cytochrome P450s (CYP450s) and neuro target enzyme Acetylcholinesterase (AChE), as well as the expressions of seven genes (CRBXase, CYP306A1, CYP6AS14, apidaecin, defensing-2, vtg, and gp-93) associated with detoxification metabolism, immune response, development, and endoplasmic reticulum stress, were significantly altered in the combined treatment compared with the corresponding individual exposures of THI or CYP. These data indicated that a mixture of THI and CYP could disturb the physiological homeostasis of honey bees. Our study provides a theoretical basis for in-depth studies on the impacts of pesticide mixtures on the health of honey bees. Our study also provides important guidance for the rational application of pesticide mixtures to protect pollinators in agricultural production effectively.

Acute oral toxicity, apoptosis, and immune response in nurse bees (Apis mellifera) induced by flupyradifurone

The potential toxicity of flupyradifurone (FPF) to honey bees has been a subject of controversy in recent years. Understanding the effect of pesticides on nurse bees is important because the fitness of nurse bees is critical for in-hive activities, such as larval survival and performing hive maintenance. In order to evaluate the acute oral toxicity of flupyradifurone on nurse bees, flupyradifurone at five different concentrations was selected to feed both larvae and nurse bees. Our results showed that nurse bees were more sensitive to flupyradifurone than larvae (LD50 of the acute oral toxicity of flupyradifurone was 17.72 μg a.i./larva and 3.368 μg a.i./nurse bee). In addition, the apoptotic rates of neurons in mushroom bodies of nurse bees were significantly induced by flupyradifurone at sublethal concentrations (8 mg/L, 20 mg/L, and 50 mg/L) and the median lethal concentration LC50 (125 mg/L). The expression of immune-related genes (Hsp90, Toll-8/Tollo, and defensin) was significantly changed in exposed nurse bees at the field-realistic concentration of flupyradifurone. However, three detoxifying enzyme genes (CYP9Q1, -2, and -3) were not affected by pesticide exposure. Our data suggest that although flupyradifurone had a relatively lower acute oral toxicity than many other common pesticides, exposures to the field-realistic and other sublethal concentrations of flupyradifurone still have cytotoxicity and immune-responsive effects on nurse bees. Therefore, flupyradifurone should be considered for its application in crops.

Mixture toxicities of tetrachlorantraniliprole and tebuconazole to honey bees (Apis mellifera L.) and the potential mechanism

The extensive use of pesticides has negative effects on the health of insect pollinators. Although pollinators in the field are seldom exposed to individual pesticides, few reports have assessed the toxic impacts of pesticide combinations on them. In this work, we purposed to reveal the combined impacts of tetrachlorantraniliprole (TET) and tebuconazole (TEB) on honey bees (Apis mellifera L.). Our data exhibited that TET had greater toxicity to A. mellifera (96-h LC₅₀ value of 298.2 mg a.i. L^-1) than TEB (96-h LC₅₀ value of 1,841 mg a.i. L^-1). The mixture of TET and TEB displayed acute synergistic toxicity to the pollinators. Meanwhile, the activities of CarE, CYP450, trypsin, and sucrase, as well as the expressions of five genes (ppo, abaecin, cat, CYP4G11, and CYP6AS14) associated with immune response, oxidative stress, and detoxification metabolism, were conspicuously altered when exposed to the mixture relative to the individual exposures. These results provided an overall comprehension of honey bees upon the challenge of sublethal toxicity between neonicotinoid insecticides and triazole fungicides and could be used to assess the intricate toxic mechanisms in honey bees when exposed to pesticide mixtures. Additionally, these results might guide pesticide regulation strategies to enhance the honey bee populations.

Inflammatory bowel disease-associated Escherichia coli strain LF82 in the damage of gut and cognition of honeybees

Patients with inflammatory bowel disease (IBD) are often accompanied with some cognitive impairment, but the mechanism is unclear. By orally exposing honeybees (Apis mellifera) to IBD-associated Escherichia coli LF82 (LF82), and non-pathogenic Escherichia coli MG1655 (MG1655) as the normal strain, we investigated whether and how LF82 induces enteritis-like manifestations and cognitive behavioral modifications in honeybees using multiparametric analysis. LF82 significantly increased gut permeability, impaired learning and memory ability in olfactory proboscis extension response conditioning, and shortened the lifespan of honeybees. Compared to MG1655, LF82 reduced the levels of tryptophan metabolism pathway substances in the honeybee gut. LF82 also upregulated genes involved in immune and apoptosis-related pathways and downregulated genes involved in G protein-coupled receptors in the honeybee brain. In conclusion, LF82 can induce enteritis-like manifestations and cognition impairment through gut metabolites and brain transcriptome alteration in honeybees. Honeybees can serve as a novel potential model to study the microbiota-gut-brain interaction in IBD condition.

The flavonoid rutin protects against cognitive impairments by imidacloprid and fipronil

The ongoing decline of bee populations and its impact on food security demands integrating multiple strategies. Sublethal impairments associated with exposure to insecticides, affecting the individual and the colony levels, have led to insecticide moratoria and bans. However, legislation alone is not sufficient and remains a temporary solution to an evolving market of insecticides. Here, we asked whether bees can be prophylactically protected against sublethal cognitive effects of two major neurotoxic insecticides, imidacloprid and fipronil, with different mechanisms of action. We evaluated the protective effect of the prophylactic administration of the flavonoid rutin, a secondary plant metabolite, present in nectar and pollen, and known for its neuroprotective properties. Following controlled or ad libitum administration of rutin, foragers of the North American bumble bee Bombus impatiens received oral administration of the insecticides at sublethal realistic dosages. Learning acquisition, memory retention and decision speed were evaluated using olfactory absolute conditioning of the proboscis extension response. We show that the insecticides primarily impair acquisition but not retention or speed of the conditioned proboscis extension response. We further show that the administration of the flavonoid rutin successfully protects the bees against impairments produced by acute and chronic administration of insecticides. Our results suggest a new avenue for the protection of bees against sublethal cognitive effects of insecticides.

Highlighted Article: Prophylactically feeding bumble bees with rutin protects their learning and memory performance against oral exposure to insecticides with different mechanisms of action.

Chronic exposure to insecticides impairs honeybee optomotor behaviour

Honeybees use wide-field visual motion information to calculate the distance they have flown from the hive, and this information is communicated to conspecifics during the waggle dance. Seed treatment insecticides, including neonicotinoids and novel insecticides like sulfoxaflor, display detrimental effects on wild and managed bees, even when present at sublethal quantities. These effects include deficits in flight navigation and homing ability, and decreased survival of exposed worker bees. Neonicotinoid insecticides disrupt visual motion detection in the locust, resulting in impaired escape behaviors, but it had not previously been shown whether seed treatment insecticides disrupt wide-field motion detection in the honeybee. Here, we show that sublethal exposure to two commonly used insecticides, imidacloprid (a neonicotinoid) and sulfoxaflor, results in impaired optomotor behavior in the honeybee. This behavioral effect correlates with altered stress and detoxification gene expression in the brain. Exposure to sulfoxaflor led to sparse increases in neuronal apoptosis, localized primarily in the optic lobes, however there was no effect of imidacloprid. We propose that exposure to cholinergic insecticides disrupts the honeybee's ability to accurately encode wide-field visual motion, resulting in impaired optomotor behaviors. These findings provide a novel explanation for previously described effects of neonicotinoid insecticides on navigation and link these effects to sulfoxaflor for which there is a gap in scientific knowledge.

Exposure to the novel insecticide flupyradifurone impairs bumblebee feeding motivation, learning, and memory retention

Bees are vital pollinators of crops and wildflowers and as such, wild bee declines threaten food security and functioning ecosystems. One driver of bee declines is the use of systemic insecticides, such as commonly used neonicotinoids. However, rising pest resistance to neonicotinoids, and restrictions on their use in the EU, has increased the demand for replacement insecticides to control crop pests. Flupyradifurone is a novel systemic insecticide that is thought to be relatively 'bee safe' although it can be present in the nectar and pollen of bee-attractive crops. Bumblebees rely on learning to forage efficiently, and thus detriments to learning performance may have downstream consequences on their ability to forage. While neonicotinoids negatively influence bumblebee learning and memory, whether this is also the case for their replacements is unclear. Here, we exposed bumblebees (Bombus impatiens) to an acute, field-realistic dose of flupyradifurone before training them to learn either an olfactory or colour association. We found that flupyradifurone impaired bumblebees' learning and memory performance in both olfactory and visual modalities. Flupyradifurone-treated bees were also less motivated to feed. Given the similarity between the detriments to cognition found here and those previously reported for neonicotinoids, this implies that these insecticides may have similar sub-lethal effects on bees. Restrictions on neonicotinoid use are therefore unlikely to benefit bees if novel insecticides like flupyradifurone are used as an alternative, highlighting that current agrochemical risk assessments are not protecting bees from the unwanted consequences of pesticide use. Sub-lethal assessments on non-Apis bees should be made mandatory in agrochemical regulation to ensure that novel insecticides are indeed 'bee safe'.

Eucalyptol relieves imidacloprid-induced autophagy through the miR-451/Cab39/AMPK axis in Ctenopharyngodon idellus kidney cells†

Imidacloprid (IMI) is a widely used neonicotinoid insecticide that has toxic effects on nontarget organisms. 1,8-Cineole (eucalyptol) is purified from essential oils in several aromatic plants and can prevent xenobiotic toxicity. The kidney is a major organ for xenobiotic elimination and thus has high risk of exposure. The purpose of this research was to clarify the effect of IMI exposure on autophagy in fish kidney cells, determine the potential of eucalyptol to provide cytoprotection from the toxicity of the neonicotinoid pesticide IMI, and identify its mechanism of action. Therefore, the Ctenopharyngodon idellus kidney cell line (CIK cell) was treated with 20 mg/L IMI and/or 20 μM eucalyptol for 48 h as the research objective. The results showed that IMI exposure induced autophagy accompanied by advanced autophagy markers BNIP3, Beclin1 and LC3Ⅱ/Ⅰ in CIK cells, reduced the levels of miR-451, increased the expression of Cab39 and AMPK, inhibited AKT/mTOR signaling, and activated the JNK pathway. Eucalyptol treatment alleviated IMI-induced autophagy and relieved the activation of autophagy-associated signals. These results indicate that eucalyptol could alleviate IMI-induced autophagy through the miR-451/Cab39/AMPK axis in fish kidney cells. These results partly explained the mechanism of biological threat on fish under IMI exposure and the potential application value of EUC in aquaculture.

Melatonin enhances the antioxidant capacity to rescue the honey bee Apis mellifera from the ecotoxicological effects caused by environmental imidacloprid

Imidacloprid severely poisons the nontarget insect honey bee Apis mellifera. Few treatments are available to mitigate the adverse effects of imidacloprid. The primary concern is that the molecular understanding of imidacloprid toxicity is not comprehensive enough. Oxidative stress is the primary pathophysiological mechanism by which pesticides cause high mortality. Our pilot study found for the first time that imidacloprid stimulates bee brains to secrete melatonin, a free radical scavenger. However, the molecular basis for imidacloprid toxicity and the role of melatonin in coping with imidacloprid have not been systematically investigated in bees. This study administered an environmental dose of imidacloprid (36 ng/bee) orally to A. mellifera. The detoxification gene cytochrome P450 CYP4G11 was significantly induced. However, potent cytotoxicity of imidacloprid suppressed the expression of the antioxidants catalase (CAT) and thioredoxin reductase (TrxR), and the activity of guaiacol peroxidase (GPX), superoxide dismutase (SOD), and reduced glutathione (GSH) was not induced. The levels of reactive oxygen species (ROS) and the lipid peroxidation marker malondialdehyde (MDA) were increased. The expression of the apoptotic genes cysteinyl aspartate specific proteinase (Caspase-3) and apoptosis inducing factor (AIF) increased, and the apoptotic features of midgut cells were prominently apparent. These results suggest that imidacloprid disrupts the bee antioxidant system, causing severe oxidative stress and tissue damage and ultimately leading to apoptosis. Significantly, however, imidacloprid exposure also stimulated bee brains to continuously secrete melatonin. Further preadministration of exogenous melatonin (200 ng/bee) orally to bees significantly reversed and enhanced the activity of the imidacloprid-suppressed antioxidants CAT, SOD, and GSH, which allowed imidacloprid-induced ROS accumulation to be effectively alleviated. The MDA content, apoptotic genes Caspase-3 and AIF, and detoxification gene CYPG411 expression were restored to normalization; midgut cell damage, apoptosis, and mortality were significantly reduced. These findings strongly suggest that melatonin enhanced bee antioxidant capacity, thus attenuating oxidative stress and apoptosis to confer imidacloprid tolerance to honey bees. Melatonin secretion may be a defense mechanism to mitigate imidacloprid toxicity.

Screening the immunotoxicity of different food preservative agents on the model organism Galleria mellonella L. (Lepidoptera: Pyralidae) larvae

Immunotoxic effects of sodium benzoate (SB, E211), sodium nitrate (SNa, E251), and sodium nitrite (SNi, E250), a few of the most common food preservatives, on the model organism Galleria mellonella L. (Lepidoptera: Pyralidae) larvae were investigated in this study. The last instar larvae were used for all experimental analyses. For this purpose, median lethal doses of SB, SNa, and SNi were applied to the larvae by the force-feeding method. We found that force-feeding G. mellonella larvae with SB, SNa, and SNi significantly reduced the larval total hemocyte counts, prohemocyte, and granulocyte ratios but increased plasmatocyte, spherulocyte, and oenocyte ratios, as well as the hemocyte mitotic indices and micronucleus frequency. The spreading ability of hemocytes and hemocyte-mediated immune responses were lower in the SB, SNa-, and SNi-treated larval groups compared to controls. Apoptotic indices were higher in all larval groups treated with food preservatives, but increments in necrotic indices were only significantly higher in SNi-treated larvae compared to controls. Our research shows that SB, SNa, and SNi have immunotoxic and cytotoxic potential on G. mellonella larvae. Thus, we suggest that G. mellonella larvae can be used as preliminary in vivo models to screen the immunotoxic effects of food preservative agents.

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.

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.

Copper and zinc impact on stress biomarkers and growth parameters in a model organism, Galleria mellonella larvae

The objective of the present study was to investigate the impact of zinc and copper on some biomarkers in a model organism Galleria mellonella L. We investigated the effects of Cu and Zn (10, 50, and 100 mg/100 g diets) on different biomarkers such as oxidative stress parameters (SOD and CAT activities and MDA levels), energy resources (protein, lipid and glycogen levels), electrolyte contents (Ca, Na, and K levels), total hemocyte count (THC), and growth and development of G. mellonella. Additionally, the accumulation levels of the used metals were also studied. Cu caused a significant decrease in protein, lipid and glycogen levels. SOD and CAT activities significantly increased at all concentrations of Cu, while they significantly increased at only high concentrations of Zn (50 and 100 mg). Lipid peroxidation levels (MDA) significantly elevated at high concentrations of both metals. It was determined that the Cu and Zn accumulation increased depending on the increase of the concentration. Zn caused an alteration in Ca level at the concentrations of 50 and 100 mg, and K and Na levels at all concentrations. While, THC significantly reduced at all Cu concentrations, this reduction was observed only at higher Zn concentrations (50 and 100 mg). Larval and pupal development time significantly extended at the highest concentration (100 mg) of Cu, and females' lifespan significantly shortened at all concentrations of Cu. Zinc caused an extension in larval development time at the highest concentration (100 mg), and caused a shortening in females and males' lifetime at all concentrations. The observed changes in biomarkers can be used as the illustration of potential toxic effects of high levels of Cu and Zn in organisms.

Caste-specific gene expression underlying the differential adult brain development in the honeybee Apis mellifera

Apis mellifera adult workers feature more developed key brain regions than queens, which allows them to cope with the broad range of duties they need to perform in a colony. However, at the end of larval development, the brain of queens is largely more developed than that of workers. Major morphogenetic changes take place after metamorphosis that shift caste-specific brain development. Here, we tested the hypothesis that this phenomenon is hormonally governed and involves differential gene expression. Our molecular screening approach revealed a set of differentially expressed genes in Pp (first pharate-adult phase) brains between castes mainly coding for tissue remodelling and energy-converting proteins (e.g. hex 70a and ATPsynβ). An in-depth qPCR analysis of the transcriptional behaviour during pupal and pharate-adult developmental stage in both castes and in response to artificially augmented hormone titres of 18 genes/variants revealed that: i. subtle differences in hormone titres between castes might be responsible for the differential expression of the EcR and insulin/insulin-like signalling (IIS) pathway genes; ii. the morphogenetic activity of the IIS in brain development must be mediated by ILP-2, iii. which together with the tum, mnb and caspase system, can constitute the molecular effectors of the caste-specific opposing brain developmental trajectories.

Effects of Selenium and Vitamin E on Enzymatic, Biochemical, and Immunological Biomarkers in Galleria mellonella L

To understand the effects of micronutrients have particular biological functions that are involved mainly in the antioxidant system, which has essential implications for the development of diseases, this study investigated how vitamin E, selenium, and their combination affect lipid, protein, carbohydrate, and malondialdehyde (MDA) content; antioxidant enzyme (catalase [CAT], superoxide dismutase [SOD], glutathione-S-transferase [GST]) activity; and the total hemocyte count (THC) in larvae of Galleria mellonella L. fed different diets. Diet 1 (100 µg of selenium) significantly decreased carbohydrate and lipid content. Diets 2 (100 µg of vitamin E), 3 (100 µg of selenium and vitamin E each), and 5 (Tween 80) did not significantly affect protein and carbohydrate content. Diet 2 significantly increased the lipid content compared to diet 4 (control). Diet 1 increased CAT, SOD, and GST activity and MDA content (highest at 27.64 nmol/mg protein). Diet 2 significantly decreased SOD activity and MDA content compared to other diets. Diet 1 significantly decreased the THC compared to other diets. These results suggested that selenium changes oxidative stress parameters, energy reserves, and THC in G. mellonella. These changes could be a physiological adaptation against selenium-induced oxidative stress. Vitamin E could play a protective role in selenium toxicity.

Field rates of Sivanto™ (flupyradifurone) and Transform® (sulfoxaflor) increase oxidative stress and induce apoptosis in honey bees (Apis mellifera L.)

Pesticide exposures can have detrimental impacts on bee pollinators, ranging from immediate mortality to sub-lethal impacts. Flupyradifurone is the active ingredient in Sivanto™ and sulfoxaflor is the active ingredient in Transform®. They are both relatively new insecticides developed with an intent to reduce negative effects on bees, when applied to bee-attractive crops. With the growing concern regarding pollinator health and pollinator declines, it is important to have a better understanding of any potential negative impacts, especially sub-lethal, of these pesticides on bees. This study reports novel findings regarding physiological stress experienced by bees exposed to field application rates of these two insecticides via a Potter Tower sprayer. Two contact exposure experiments were conducted-a shorter 6-hour study and a longer 10-day study. Honey bee mortality, sugar syrup and water consumption, and physiological responses (oxidative stress and apoptotic protein assays) were assessed in bees exposed to Sivanto™ and Transform®, and compared to bees in control group. For the longer, 10-day contact exposure experiment, only the Sivanto™ group was compared to the control group, as high mortality recorded in the sulfoxaflor treatment group during the shorter contact exposure experiment, made the latter group unfeasible to test in the longer 10-days experiment. In both the studies, sugar syrup and water consumptions were significantly different between treatment groups and controls. The highest mortality was observed in Transform® exposed bees, followed by the Sivanto™ exposed bees. Estimates of reactive oxygen/nitrogen species indicated significantly elevated oxidative stress in both pesticide treatment groups, when compared to controls. Caspase-3 protein assays, an indicator of onset of apoptosis, was also significantly higher in the pesticide treatment groups. These differences were largely driven by post exposure duration, indicating sub-lethal impacts. Further, our findings also emphasize the need to revisit contact exposure impacts of Sivanto™, given the sub-lethal impacts and mortality observed in our long-term (10-day) contact exposure experiment.

Effect of Oral Administration of 1,3-1,6 β-Glucans in DWV Naturally Infected Newly Emerged Bees (Apis mellifera L.)

Honeybee pathogens have an important role in honeybee colony mortality and colony losses; most of them are widely spread and necessitate worldwide solutions to contrast honeybee's decline. Possible accepted solutions to cope with the spread of honeybee's pathogens are focused on the study of experimental protocols to enhance the insect's immune defenses. Honeybee's artificial diet capable to stimulate the immune system is a promising field of investigation as ascertained by the introduction of 1,3-1,6 β-glucans as a dietary supplement. In this work, by collecting faecal samples of honeybees exposed to different dietary conditions of 1,3-1,6 β-glucans (0.5% and 2% w/w), it has been possible to investigate the Deformed wing virus (DWV) viral load kinetic without harming the insects. Virological data obtained by a one-step TaqMan RT-PCR highlighted the ability of 1,3-1,6 β-glucans to reduce the viral load at the 24th day of rearing. The results indicated that the diet supplemented with 1,3-1,6 β-glucans was associated with a dose-dependent activation of phenoloxidase. The control group showed a higher survival rate than the experimental groups. This research confirmed 1,3-1,6 β-glucans as molecules able to modulate honeybees' defense pathways, and this is the first report in which the kinetic of DWV infection in honeybee faeces has been monitored by a RT-qPCR.

Flumethrin at sublethal concentrations induces stresses in adult honey bees (Apis mellifera L.)

Flumethrin is a typical pyrethroid varroacide widely used for mite control in beekeeping worldwide. Currently, information on the toxicological characteristics of flumethrin on bees at sublethal concentrations is still lacking. To fill this gap in information, we performed a 48-h acute oral and 14-day chronic toxicity testing of flumethrin in newly emerged adult honey bees under laboratory conditions. Results showed that flumethrin had high acute toxicity to honey bees with a 48-h LD₅₀ of 0.47 µg/bee (95% CI, 0.39 ∼ 0.57 µg/bee), which is higher than that of many other commercial pyrethroid insecticides, but lower than that of tau-fluvalinate. After 14 days of chronic exposure to flumethrin at 0.01, 0.10, and 1.0 mg/L, significant antioxidant response, detoxification, immune reaction, and apoptosis were observed in the midguts. These findings indicated that flumethrin had potential risks to bees, and it can disturb the homeostasis of bees at sublethal concentrations under longer exposure conditions. Flumethrin is highly lipophilic and easy to accumulate in beeswax; thus, careless practices might pose risks to colony development in commercial beekeeping and native populations. This laboratory study can serve as an early warning, and further studies are required to understand the real residual level of flumethrin in bees and the risks of flumethrin in field condition.

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.

Thiamethoxam-mediated alteration in multi-biomarkers of a model organism, Galleria mellonella L. (Lepidoptera: Pyralidae)

Thiamethoxam (TMX), a second-generation neonicotinoid, is extensively used to control numerous pests that infest crops. We investigated the effects of TMX (10, 20, 30, 40, and 50 μg/mL for 24, 48, 72, and 96 h) on biomarkers such as antioxidant enzymes (superoxide dismutase (SOD) and catalase (CAT)); malondialdehyde (MDA), protein, lipid, and carbohydrate levels; micronucleus formation; and total hemocyte count in a model organism, Galleria mellonella L. SOD and CAT activities significantly decreased after 72 and 96 h of treatment at all TMX concentrations compared with control. MDA level increased following treatment with all TMX doses, with the exception of that following treatment with the lowest dose (10 μg/mL) at all tested treatment durations. Lipid and carbohydrate levels significantly decreased following treatment with high doses of TMX (40 and 50 μg/mL) after 48, 72, and 96 h. Micronucleated cell number significantly increased following treatment with all TMX doses at all tested treatment durations, except with 10 μg/mL of TMX for 24 h, when compared with control. During the first 72 h, total hemocyte count significantly decreased following treatment with 20-, 30-, 40-, and 50-μg/mL TMX; however, it was significantly reduced at all doses of TMX after 96 h. These results suggest that TMX can induce immunotoxicity, oxidative stress, and genotoxicity in a potential target and also in the model organism, G. mellonella. In addition, our study provides additional information regarding the prospective toxic effects of TMX.

Boric acid-induced immunotoxicity and genotoxicity in model insect Galleria mellonella L. (Lepidoptera: Pyralidae)

Boric acid (BA) is widely used in various industrial process and can be accessed to nontarget organisms. This study aimed to investigate the insecticidal effects of BA and its toxic activities with respect to immunologic and genotoxic effects using Galleria mellonella larvae as a model. BA concentrations (78.125-10,000 ppm) were administrated to the larvae using the feeding method. Concentration-dependent mortality was observed in all larval groups. Probit analysis revealed LC₃₀ , LC₅₀ , and LC₇₀ values to be 112.4, 320.1, and 911.4 ppm, respectively. These concentrations were used in all bioassays. Drastic reductions in total hemocyte counts along with changes in differential hemocyte counts were observed following BA treatment. Cell viability assays showed dose-dependent reductions in viable cells and an increase in the necrotic and apoptotic ratios after BA treatment. However, mitotic indices of larval hemocytes did not change at all BA concentrations. The cytotoxic effect of BA led to a significant reduction in cellular immune responses such as encapsulation, melanization, and nodulation activities of treated larvae. While BA increased micronucleus ratios at the highest concentration, comet parameters indicating DNA damage increased in G. mellonella larval hemocytes at all concentrations. These report that BA suppresses the immune system of G. mellonella and also poses risks of genotoxicity at high concentrations.

Spinosad-mediated effects on survival, overall group activity and the midgut of workers of Partamona helleri (Hymenoptera: Apidae)

Populations of stingless bees have declined around the world and pesticides have been indicated as one of the possible causes of this decrease. Spinosad, which is synthesized from the fermentation process produced by the soil actinomycete Saccharopolyspora spinosa, is one of the most used bioinsecticides today. This study aimed to evaluate the possible effects of spinosad (formulation) on survival, general group activity and the processes of autophagy, apoptosis and oxidative stress in two organs (midgut and brain) of workers of Partamona helleri, after 24 h of oral exposure. Workers were orally exposed to different concentrations of spinosad. The concentration (8.16 × 10^-3 mg a.i./mL) that led to the mortality of approximately half the number of treated bees was considered LC₅₀ and was used in behavior, histology and immunofluorescence bioassays. The results revealed that bee survival was substantially reduced with increasing spinosad concentrations. The LC₅₀ of the bioinsecticide compromised general group activity, caused morphological alterations in the midgut and intensified the processes of autophagy, apoptosis and oxidative stress in this organ. The brain, on the other hand, did not present significant alterations under the tested conditions. The data obtained demonstrate, therefore, that spinosad negatively affects individual survival, general group activity and the midgut epithelium of P. helleri.

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.

Imidacloprid Impacts on Neurobehavioral Performance, Oxidative Stress, and Apoptotic Events in the Brain of Adolescent and Adult Rats

Currently, imidacloprid (IMI) is the first insecticide and the second agrochemical highly applied all over the world. Here, we report on the impacts of IMI on neurobehavioral performance, oxidative stress, and apoptotic changes in the brain in either adult or adolescent rats. Forty male rats (adult and adolescent) were allocated to four groups. IMI groups were orally given 1 mg IMI/kg b.wt. dissolved in corn oil, whereas the controls were orally administered corn oil daily for 60 days. The obtained results demonstrated that IMI exposure resulted in less exploratory activity, deficit sensorimotor functions, and high depression. Levels of neurotransmitter including serotonin, gamma-aminobutyric acid, and dopamine were significantly reduced. Oxidative damage of brain tissues was evident following IMI exposure represented by the high levels of protein carbonyl, 8-hydroxyguanosine, and malondialdehyde, but total antioxidant capacity was reduced. Histopathological investigations of the brain tissues of IMI treated group revealed varying degrees of degeneration of the neuron. The immunohistochemical evaluation revealed a strong presence of glial fibrillary acidic protein (GFAP) and Bax positive cells, but a low expression of Bcl-2. These injurious impacts of IMI were very prominent in the adult rats than in the adolescent rats. Conclusively, exposure to IMI even at very low concentration could induce multiple neurobehavioral aberrations and neurotoxic impacts, especially in adults.

Non-target toxicity of novel insecticides

Humans have used insecticides since ancient times. The spectrum and potency of available insecticidal substances has greatly expanded since the industrial revolution, resulting in widespread use and unforeseen levels of synthetic chemicals in the environment. Concerns about the toxic effects of these new chemicals on non-target species became public soon after their appearance, which eventually led to the restrictions of use. At the same time, new, more environmentally-friendly insecticides have been developed, based on naturally occurring chemicals, such as pyrethroids (derivatives of pyrethrin), neonicotinoids (derivatives of nicotine), and insecticides based on the neem tree vegetable oil (Azadirachta indica), predominantly azadirachtin. Although these new substances are more selective toward pest insects, they can still target other organisms. Neonicotinoids, for example, have been implicated in the decline of the bee population worldwide. This review summarises recent literature published on non-target toxicity of neonicotinoids, pyrethroids, and neem-based insecticidal substances, with a special emphasis on neonicotinoid toxicity in honeybees. We also touch upon the effects of pesticide combinations and documented human exposure to these substances.

The functions of caspase in whitefly Bemisia tabaci apoptosis in response to ultraviolet irradiation

Whiteflies (Bemisia tabaci) are phloem feeders, and some invasive species are composed of cryptic species complexes that cause extensive crop damage, particularly via the direct transmission of plant viruses. Apoptosis is a type of programmed cell death essential for organismal development and tissue homeostasis. The caspases belong to a family of cysteine proteases that play a central role in the initiation of apoptosis in many organisms. Here, we employed a comprehensive genomics approach to identity caspases in B. tabaci Middle East Asia Minor 1 (MEAM1), an invasive whitefly that carries a cryptic species complex that is devastating to crops. Four caspase genes were identified, and their motif compositions were predicted. Structures were relatively conserved in both putative effector and initiator caspases. Expression patterns of caspase genes differed across insect developmental stages. Three caspase genes were induced immediately after ultraviolet (UV) treatment. Expression levels of Bt-caspase-1 and Bt-caspase-3b increased in the midgut and salivary glands during apoptosis induced by UV treatments, whereas silencing of both genes reduced UV-triggered apoptosis. Our study demonstrates that Bt-caspase-1 and Bt-caspase-3b, respectively, act as putative initiator and effector apoptotic caspases in the MEAM1 whitefly.

Imidacloprid induced alterations in oxidative stress, biochemical, genotoxic, and immunotoxic biomarkers in non-mammalian model organism Galleria mellonella L. (Lepidoptera: Pyralidae)

Imidacloprid (IMI), a neonicotinoid insecticide, is widely used to control pests in agriculture. We investigated the changes in antioxidant enzyme activities, lipid peroxidation levels, biochemical effects, genotoxic effect, and immunotoxic effect of sublethal doses (0.25, 0.50, 0.75, and 1.00 µg) of IMI at different time periods (24, 48, 72, and 96 h) on a model organism, Galleria mellonella L. The results indicated that there were dose-dependent increases in both antioxidant enzyme activities (SOD and CAT) and MDA levels. Protein content was not affected by IMI at 24th and 48th, whereas it was decreased by the highest dose of IMI (1.00 µg) at 72nd and 96th h. Lipid and carbohydrate contents were reduced with increasing doses of IMI. Micronucleus frequency significantly increased in all IMI doses. All IMI doses caused a significant decrease in THC at 24th, 48th, and 72nd h. Our results can help to illustrate the effects of IMI in target organisms and indirectly may aid to discover potential risk of it on nontarget organisms. Future studies, at molecular levels, will be helpful in understanding the mechanism of action of IMI on these biomarkers.

Lethal and sublethal effects of insecticides on Engytatus varians (Heteroptera: Miridae), a predator of Tuta absoluta (Lepidoptera: Gelechiidae)

The mirid Engytatus varians (Distant) is a promising biological control agent of the tomato borer, Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae), one of the most destructive pests of tomato (Solanum lycopersicum L.). The effects of five insecticides commonly used on tomato crops in Brazil were evaluated on E. varians in laboratory and semifield conditions. Glass Petri dish with residues of chlorfenapyr, thiamethoxam, and abamectin caused ˃90% mortality in both stages of the predator 72 h post-treatment, except imidacloprid that caused 78% of nymphs mortality. Teflubenzuron caused 24 and 66% mortality on adults and nymphs, respectively. The offspring of females derived from treated nymphs with teflubenzuron was significantly lower than the control but not when females were treated as adults. Longevity of males derived from nymphs treated with teflubenzuron was significantly reduced, but no effects were observed on females. When males and females were treated as adults with teflubenzuron there were no effects on their longevity. In the greenhouse-aged tomato plants, the 2 h-old residues of thiamethoxam, chlorfenapyr, and abamectin caused more than 70% of mortality of third instar of E. varians at 72 h post-treatment, 12 day-old residues of all three compounds caused a mortality lower than 30%. These data suggest that teflubenzuron can be associated with releases of E. varians adults, while the use of other evaluated pesticides should be avoided in this situation. Although, the low persistence of these products indicate that their spraying and later releases of E. varians adults on tomato crops are a possible strategy to control T. absoluta.

Imidacloprid slows the development of preference for rewarding food sources in bumblebees (Bombus impatiens)

Bee pollination is economically and ecologically vital and recent declines in bee populations are therefore a concern. One possible cause of bee declines is pesticide use. Bumblebees exposed to imidacloprid, a neonicotinoid pesticide, have been shown to be less efficient foragers and collect less pollen on foraging trips than unexposed bees. We investigated whether bumblebees (Bombus impatiens) chronically exposed to imidacloprid at field-realistic levels of 2.6 and 10 ppb showed learning deficits that could affect foraging. Bumblebees were tested for their ability to associate flower colour with reward value in a simulated foraging environment. Bumblebees completed 10 foraging trips in which they collected sucrose solution from artificial flowers that varied in sucrose concentration. The reward quality of each artificial flower was predicted by corolla colour. Unexposed bumblebees acquired a preference for feeding on the most rewarding flower colour on the second foraging trip, while bumblebees exposed at 2.6 and 10 ppb did not until their third and fifth trip, respectively. The delay in preference acquisition in exposed bumblebees may be due to reduced flower sampling and shorter foraging trips. These results show that bumblebees exposed to imidacloprid are slow to learn the reward value of flowers and this may explain previously observed foraging inefficiencies associated with pesticide exposure.

Azadirachtin Affects the Growth of Spodoptera litura Fabricius by Inducing Apoptosis in Larval Midgut

Azadirachtin, the environmentally friendly botanical pesticide, has been used as an antifeedant and pest growth regulator in integrated pest management for decades. It has shown strong biological activity against Spodoptera litura, but the mechanism of toxicity remains unclear. The present study showed that azadirachtin inhibited the growth of S. litura larvae, which was resulted by structure destroy and size inhibition of the midgut. Digital gene expression (DGE) analysis of midgut suggested that azadirachtin regulated the transcriptional level of multiple unigenes involved in mitogen-activated protein kinase (MAPK) and calcium apoptotic signaling pathways. Simultaneously, the expression patterns of some differentially expressed unigenes were verified by quantitative real time-PCR (qRT-PCR). In addition, the enhanced terminal deoxynucleotidyl transferase biotin-dUTP nick end labeling (TUNEL) staining, the increased expression of caspase family members and apoptosis-binding motif 1 (IBM1) on both gene and protein level and the release of cytochrome c from mitochondria to cytoplasm were induced in midgut after azadirachtin treatment. These results demonstrated that azadirachtin induced structural alteration in S. litura larval midgut by apoptosis activation. These alterations may affect the digestion and absorption of nutrients and eventually lead to the growth inhibition of larvae.

Imidacloprid exposure cause the histopathological changes, activation of TNF-α, iNOS, 8-OHdG biomarkers, and alteration of caspase 3, iNOS, CYP1A, MT1 gene expression levels in common carp (Cyprinus carpio L.)

•

IMI toxication was evaluated with three different methods.

•

Pathological lesions were observed after IMI exposure in gills, liver and brain.

•

IMI exposure induced iNOS, 8-OHdG and TNF-α activation in gills, liver and brain.

•

IMI exposure caused upregulation iNOS, caspase 3 and MT1 expressions in brain.

Imidacloprid (IMI) is a neonicotinoid that is widely used for the protection of crops and carnivores from insects and parasites, respectively. It is well known that imidacloprid exposure has a harmful effect on several organisms. However, there is little information about imidacloprid toxicity in aquatic animals, particularly fish. Thus, in the current study, we assessed the histopathological changes; activation of iNOS, 8-OHdG and TNF-α; and expression levels of caspase 3, iNOS, CYP1A and MT1 genes in the common carp exposed to imidacloprid. For this purpose, fish were exposed to either a low dose (140 mg/L) or a high dose (280 mg/L) of imidacloprid for 24 h, 48 h, 72 h and 96 h. After IMI exposure, we detected hyperplasia of secondary lamellar cells and mucous cell hyperplasia in the gills, as well as hydropic degeneration in hepatocytes and necrosis in the liver. Moreover, 8-OHdG, iNOS and TNF-α activation was found particularly in the gills and liver but also moderately in the brain. Transcriptional analysis showed that caspase 3 expression was altered low dose and high doses of IMI for 72 h and 96 h exposure (p < 0.05), iNOS expression was up-regulated with both low and high doses of IMI and in a time-dependent manner (p < 0.05, p < 0.01, p < 0.001), CYP1A expression was not significantly changed regardless of the dose of IMI and exposure time (p > 0.05) except with low and high doses of IMI for 96 h (p < 0.05), and lastly, MT1 gene expression was up-regulated only in the brain with low doses of IMI for 96 h and high doses of IMI for 48 h, 72 h and 96 h exposure (p < 0.05, p < 0.01). Our results indicated that acute IMI exposure moderately induce apoptosis in the brain but caused severe histopathological lesions, inflammation, and oxidative stress in the gills, liver, and brain of the common carp.

The exposure of honey bees (Apis mellifera; Hymenoptera: Apidae) to pesticides: Room for improvement in research

Losses of honey bees have been repeatedly reported from many places worldwide. The widespread use of synthetic pesticides has led to concerns regarding their environmental fate and their effects on pollinators. Based on a standardised review, we report the use of a wide variety of honey bee matrices and sampling methods in the scientific papers studying pesticide exposure. Matrices such as beeswax and beebread were very little analysed despite their capacities for long-term pesticide storage. Moreover, bioavailability and transfer between in-hive matrices were poorly understood and explored. Many pesticides were studied but interactions between molecules or with other stressors were lacking. Sampling methods, targeted matrices and units of measure should have been, to some extent, standardised between publications to ease comparison and cross checking. Data on honey bee exposure to pesticides would have also benefit from the use of commercial formulations in experiments instead of active ingredients, with a special assessment of co-formulants (quantitative exposure and effects). Finally, the air matrix within the colony must be explored in order to complete current knowledge on honey bee pesticide exposure.

Spinosad induces autophagy of Spodoptera frugiperda Sf9 cells and the activation of AMPK/mTOR signaling pathway

Spinosad, a high-selectivity neural toxin, has been widely used in agricultural production. However, the mode of action of spinosad on insect non-neural cells is not yet clear and hence requires further investigation. Therefore, to reveal the cytotoxic mechanisms of spinosad, we investigated whether and how it can induce autophagic cell death. After treating Sf9 cells with spinosad, the resulting autophagosome was observed by transmission electron microscopy and monodansylcadaverine staining. Interestingly, spinosad induced the accumulation of Beclin-1, degradation of p62, and intensification of LC3-B formation and translocation and thus autophagy, whereas, 3-MA treatment reverted the phenotype. Under ATP depletion conditions, spinosad induced autophagy of Sf9 cells and activation of the AMPK/mTOR signaling pathway.

A sublethal dose of a neonicotinoid insecticide disrupts visual processing and collision avoidance behaviour in Locusta migratoria

Neonicotinoids are known to affect insect navigation and vision, however the mechanisms of these effects are not fully understood. A visual motion sensitive neuron in the locust, the Descending Contralateral Movement Detector (DCMD), integrates visual information and is involved in eliciting escape behaviours. The DCMD receives coded input from the compound eyes and monosynaptically excites motorneurons involved in flight and jumping. We show that imidacloprid (IMD) impairs neural responses to visual stimuli at sublethal concentrations, and these effects are sustained two and twenty-four hours after treatment. Most significantly, IMD disrupted bursting, a coding property important for motion detection. Specifically, IMD reduced the DCMD peak firing rate within bursts at ecologically relevant doses of 10 ng/g (ng IMD per g locust body weight). Effects on DCMD firing translate to deficits in collision avoidance behaviours: exposure to 10 ng/g IMD attenuates escape manoeuvers while 100 ng/g IMD prevents the ability to fly and walk. We show that, at ecologically-relevant doses, IMD causes significant and lasting impairment of an important pathway involved with visual sensory coding and escape behaviours. These results show, for the first time, that a neonicotinoid pesticide directly impairs an important, taxonomically conserved, motion-sensitive visual network.

Developmental and loco-like effects of a swainsonine-induced inhibition of α-mannosidase in the honey bee, Apis mellifera

Background

Deficiencies in lysosomal a-mannosidase (LAM) activity in animals, caused either by mutations or by consuming toxic alkaloids, lead to severe phenotypic and behavioural consequences. Yet, epialleles adversely affecting LAM expression exist in the honey bee population suggesting that they might be beneficial in certain contexts and cannot be eliminated by natural selection.

Methods

We have used a combination of enzymology, molecular biology and metabolomics to characterise the catalytic properties of honey bee LAM (AmLAM) and then used an indolizidine alkaloid swainsonine to inhibit its activity in vitro and in vivo.

Results

We show that AmLAM is inhibited in vitro by swainsonine albeit at slightly higher concentrations than in other animals. Dietary exposure of growing larvae to swainsonine leads to pronounced metabolic changes affecting not only saccharides, but also amino acids, polyols and polyamines. Interestingly, the abundance of two fatty acids implicated in epigenetic regulation is significantly reduced in treated individuals. Additionally, swainsonie causes loco-like symptoms, increased mortality and a subtle decrease in the rate of larval growth resulting in a subsequent developmental delay in pupal metamorphosis.

Discussion

We consider our findings in the context of cellular LAM function, larval development, environmental toxicity and colony-level impacts. The observed developmental heterochrony in swainsonine-treated larvae with lower LAM activity offer a plausible explanation for the existence of epialleles with impaired LAM expression. Individuals carrying such epialleles provide an additional level of epigenetic diversity that could be beneficial for the functioning of a colony whereby more flexibility in timing of adult emergence might be useful for task allocation.

Queen pheromone regulates programmed cell death in the honey bee worker ovary

In social insect colonies the presence of a queen, secreting her pheromones, is a key environmental cue for regulating the reproductive state of workers. However, until recently the proximate molecular mechanisms underlying facultative worker sterility were unidentified. Studies into worker oogenesis in the honey bee (Apis mellifera) have indicated that programmed cell death is central to the regulation of oogenesis. Here we investigate how queen pheromone, age of the worker and ovary state affect both programmed cell death and cell number in worker ovaries. We describe a novel method to simultaneously measure programmed cell death (caspase activity) and live cell number (estimated from the amount of adenosine triphosphate) in an insect tissue. Workers exposed to queen pheromone have higher levels of caspase activity in the ovary than those not exposed. Our results suggest that queen pheromone triggers programmed cell death at the mid-oogenesis checkpoint causing the abortion of worker oocytes and reproductive inhibition of the worker caste. Nonetheless, high caspase activity is present in activated ovaries from workers not exposed to queen pheromone. This caspase activity is most likely to be from the nurse cells undergoing programmed cell death, in late oogenesis, for normal oocyte development. Our study shows that the social environment of an organism can influence programmed cell death within a tissue.

Insecticide cytotoxicology in China: Current status and challenges

The insecticide cytotoxicology, as a new branch of toxicology, has rapidly developed in China. During the past twenty years, thousands of investigations have sprung up to evaluate the damages and clarify the mechanisms of insecticidal chemical substances to insect cells in vivo or in vitro. The mechanisms of necrosis, apoptosis or autophagy induced by synthetic or biogenic pesticides and virus infections have been systematically illuminated in many important models, including S2, BmN, SL-1, Sf21 and Sf9 cell lines. In addition, a variety of methods have also been applied to examine the effects of insecticides and elaborate the modes of action. As a result, many vital factors and pathways, such as cytochrome c, the Bcl-2 family and caspases, in mitochondrial signaling pathways, intracellular free calcium and lysosome signal pathways have been illuminated and drawn much attention. Benefiting from the application of insecticide cytotoxicology, natural products purifications, biological activities assessments of synthetic compounds and high throughput screening models have been accelerated in China. However, many questions remained, and there exist great challenges, especially in theory system, evaluation criterion, evaluation model, relationship between activity in vitro and effectiveness in vivo, and the toxicological mechanism. Fortunately, the generation of "omics" could bring opportunities for the development of insecticide cytotoxicology.