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

Impact of a lambda-cyhalothrin formulation residues on larval Apis mellifera: examining midgut and fat body morphological response to insecticide chronic exposure

Pollination by honey bees (Apis mellifera) is crucial for maintaining biodiversity and crop yields. However, the widespread use of pesticides may threaten bees' survival by contaminating their resources. Lambda-cyhalothrin, a neurotoxic insecticide commonly used in agricultural pest control, poses particular risks. In insects, the midgut and fat body serve as primary barriers against xenobiotics, and exposure to these chemicals during larval development can impact adult bees. This study aimed to assess whether the residual concentration of lambda-cyhalothrin in pollen grains affects the midgut and fat body of larval A. mellifera workers after chronic exposure. The midgut epithelium of larvae exposed to a lambda-cyhalothrin-based insecticide (λ-CBI) exhibited autophagic vacuoles, apical cell protrusions, apocrine secretion, nuclear pyknosis, and high levels of polysaccharides and glycoconjugates in the cytoplasm, with smaller amounts in the brush border. Histochemical analysis revealed areas of vacuolation and damage to cell integrity in the midgut. In fat body cells, the insecticide increased polysaccharide storage and decreased lipid droplet diameter. Despite the histopathological damage, no effects were found in the larval development and adult emergence. These findings suggest the occurrence of apoptosis and autophagy in midgut cells and alterations in nutrient storage in the fat body of A. mellifera larvae exposed to the λ-CBI, potentially impacting the physiology and development of this pollinator with possible effects on adult workers.

Contaminant-driven midgut histological damage in bees and other aculeate Hymenoptera: A quantitative review

We present a review about histological sub-lethal effects due to anthropogenic contaminants on the midgut of bees and other aculeate hymenopterans. Contaminant types, damage types, and methodology were extracted and summarized from 74 published articles, and then quantitatively analyzed. We found that the Western honeybee (Apis mellifera) is by far the most widely used model. Contaminants have largely been tested under laboratory conditions, particularly insecticides and fungicides. Tissue-level damage (e.g., degradation of epithelium and of peritrophic membrane) were often detected together with cell-level damage (e.g., cell vacuolisation, karyorrhexis). Descriptive statistics and mixed models suggested that herbicides may cause a specific mix of alterations with an overall lower severity compared with other pesticides, while the combined use of light and electron microscopy seemed to detect more damage types. We claim for efforts to reduce biases in future studies on such histological effects, allowing their clearer use as markers of human activities.

Effects of the insecticide thiodicarb on non-target organs and behavior of the stingless bee Partamona helleri (Hymenoptera: Meliponini)

Stingless bees are vital pollinators in the Neotropics and can be exposed to pesticides used in agriculture during their foraging activities. Among these pesticides, the insecticide thiodicarb is commonly applied to bean and sunflower crops, posing a potential risk to the stingless bee Partamona helleri, which pollinates these plants. This study aimed to investigate the effects of thiodicarb on mortality, morphology, programmed cell death signaling pathways in the midgut and Malpighian tubules, and the locomotion behavior of P. helleri workers. The estimated lethal concentration (LC50) of thiodicarb for P. helleri was 87 μg a.i. mL-1. Bees fed this concentration exhibited morphological damage to the midgut epithelium and Malpighian tubules, including brush border degeneration, increased cytoplasm vacuolation, and the release of cell fragments into the intestinal lumen. In the midgut, regenerative cells showed cytoplasm disorganization and nuclear pyknosis. Immunofluorescence analysis revealed an increase in cell death via autophagy and apoptosis in the epithelial cells of the affected organs. Ingestion of thiodicarb also altered the bees' locomotion, resulting in increased meandering and decreased walking speed and total distance traveled. These findings demonstrate that the LC50 of thiodicarb causes damage to non-target organs as the midgut and Malpighian tubules, and impairs behavior, which may ultimately affect the pollination services provided by P. helleri. These results enhance our understanding of the vulnerability of stingless bees to insecticides and underscore the importance of strategies aimed at protecting these pollinators.

Effects of sublethal concentration of thiamethoxam formulation on the wild stingless bee, Partamona helleri Friese (Hymenoptera: Apidae): Histopathology, oxidative stress and behavioral changes

Bees are pollinators of native and cultivated plants around the world. However, several factors are contributing to the decrease in their populations in recent years, with emphasis on the increasing use of insecticides in agriculture. Thiamethoxam is a neonicotinoid neurotoxicant, which binds to nicotinic acetylcholine receptors, causing hyperexcitation, paralysis and death of insects. Although thiamethoxam's target is the nervous system, it can affect other organs through ingestion, such as the midgut, affecting non-target insects such as bees. Partamona helleri Friese (Hymenoptera: Apidae) is a stingless bee, pollinator of several native and cultivated botanical families, and can be exposed to sublethal concentrations of thiamethoxam. This study evaluated the side effects of chronic oral exposure to thiamethoxam on the midgut, oxidative stress and behavior of P. helleri workers. The bees were exposed orally, for 7 days, to the approximate sublethal concentration of thiamethoxam found in pollen grains (0.09 ng/g). The results demonstrated changes in the midgut epithelium of workers treated with thiamethoxam, such as cytoplasmic vacuolization, cellular protrusions, increased apocrine transfer, mitochondrial damage, decreased proteins and neutral polysaccharides and the presence of cells undergoing autophagy and apoptosis. Sublethal concentration of thiamethoxam also induced oxidative stress, evidenced by changes in the activities of detoxification enzymes and antioxidant markers. Finally, thiamethoxam affects the bee's behavior, driving the distance covered and walking speed of this insect. The results indicate that the exposure of P. helleri workers to sublethal concentration of thiamethoxam have negative impacts upon midgut morphology and physiology and behavioral traits.

Pesticide impacts on insect pollinators: Current knowledge and future research challenges

With the need to intensify agriculture to meet growing food demand, there has been significant rise in pesticide use to protect crops, but at different rates in different world regions. In 2016, the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPBES) global assessment on pollinators, pollination and food production identified pesticides as one of the major drivers of pollinator decline. This assessment highlighted that studies on the effects of pesticides on pollinating insects have been limited to only a few species, primarily from developed countries. Given the worldwide variation in the scale of intensive agricultural practices, pesticide application intensities are likely to vary regionally and consequently the associated risks for insect pollinators. We provide the first long-term, global analysis of inter-regional trends in the use of different classes of pesticide between 1995 and 2020 (FAOSTAT) and a review of literature since the IPBES pollination assessment (2016). All three pesticide classes use rates varied greatly with some countries seeing increased use by 3000 to 4000 % between 1995 and 2020, while for most countries, growth roughly doubled. We present forecast models to predict regional trends of different pesticides up to 2030. Use of all three pesticide classes is to increase in Africa and South America. Herbicide use is to increase in North America and Central Asia. Fungicide use is to increase across all Asian regions. In each of the respective regions, we also examined the number of studies since 2016 in relation to pesticide use trends over the past twenty-five years. Additionally, we present a comprehensive update on the status of knowledge on pesticide impacts on different pollinating insects from literature published during 2016-2022. Finally, we outline several research challenges and knowledge gaps with respect to pesticides and highlight some regional and international conservation efforts and initiatives that address pesticide reduction and/or elimination.

Insecticides used for controlling cotton mealybug pose a threat to non-target bumble bees

Bumble bees (Bombus spp., Hymenoptera, Apidae) play a crucial role in pollinating greenhouse tomato crops. However, tomato production is constantly threatened by different invasive pests that often lead to the increased use of pesticides, with negative consequences for pollinators. The cotton mealybug Phenacoccus solenopsis has recently been reported in Mediterranean tomatoes and its chemical control raises concerns also regarding bumble bees. In the laboratory, we evaluated the acute toxicity and sublethal effects in B. terrestris workers exposed to the diet contaminated with four insecticides (acetamiprid, pyriproxyfen, sulfoxaflor, and thiamethoxam), potentially used to control P. solenopsis. Sulfoxaflor and thiamethoxam significantly reduced the survival of B. terrestris, while acetamiprid and pyriproxyfen altered its feeding behaviour, and the bumble bees were unable to detect the contaminated solution. Moreover, neurotoxic symptoms were observed in bees exposed to acetamiprid and alterations of the midgut were detected in bees exposed to both acetamiprid and pyriproxyfen. These results show that insecticides with low levels of toxicity to bumble bees (e.g. acetamiprid and pyriproxyfen), can cause sublethal effects on them, increasing concern about the use of these substances. Our findings provide valuable insights as regards optimizing bumble bee pollination services with chemical pest control within the context of Integrated Pest and Pollinator Management.

Acute exposure to fungicide fluazinam induces cell death in the midgut, oxidative stress and alters behavior of the stingless bee Partamona helleri (Hymenoptera: Apidae)

Stingless bees (Hymenoptera: Meliponini) are pollinators of both cultivated and wild crop plants in the Neotropical region. However, they are susceptible to pesticide exposure during foraging activities. The fungicide fluazinam is commonly applied in bean and sunflower cultivation during the flowering period, posing a potential risk to the stingless bee Partamona helleri, which serves as a pollinator for these crops. In this study, we investigated the impact of acute oral exposure (24 h) fluazinam on the survival, morphology and cell death signaling pathways in the midgut, oxidative stress and behavior of P. helleri worker bees. Worker bees were exposed for 24 h to fluazinam (field concentrations 0.5, 1.5 and 2.5 mg a.i. mL-1), diluted in 50 % honey aqueous solution. After oral exposure, fluazinam did not harm the survival of worker bees. However, sublethal effects were revealed using the highest concentration of fluazinam (2.5 mg a.i. mL-1), particularly a reduction in food consumption, damage in the midgut epithelium, characterized by degeneration of the brush border, an increase in the number and size of cytoplasm vacuoles, condensation of nuclear chromatin, and an increase in the release of cell fragments into the gut lumen. Bees exposed to fluazinam exhibited an increase in cells undergoing autophagy and apoptosis, indicating cell death in the midgut epithelium. Furthermore, the fungicide induced oxidative stress as evidenced by an increase in total antioxidant and catalase enzyme activities, along with a decrease in glutathione S-transferase activity. And finally, fluazinam altered the walking behavior of bees, which could potentially impede their foraging activities. In conclusion, our findings indicate that fluazinam at field concentrations is not lethal for workers P. helleri. Nevertheless, it has side effects on midgut integrity, oxidative stress and worker bee behavior, pointing to potential risks for this pollinator.

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.

Glyphosate-Based Herbicide Causes Cellular Alterations to Gut Epithelium of the Neotropical Stingless Bee Melipona quadrifasciata quadrifasciata (Hymenoptera: Meliponini)

Glyphosate-based herbicides (GBH) are the best-selling pesticides in Brazil, with hundreds of thousands of tons sold per year. There is no study investigating morphological alterations caused by GBH on the epithelium of the gut in bees. Here, we aimed to demonstrate effects of chronic ingestion of GBH in the midgut digestive cells of the Brazilian stingless bee Melipona quadrifasciata quadrifasciata Lepeletier 1836. We kept forager workers of M. quadrifasciata in laboratory conditions and fed on food contaminated with three different concentrations of GBH for 10 days, after which the midgut digestive cell structure and ultrastructure were analyzed. The presence of GBH in food did not affect food consumption, indicating that M. quadrifasciata bees do not reject food contaminated with GBH. As digestive cells of the midgut release apocrine secretion as a detoxication mechanism, we expected that the ingestion of food contaminated with GBH in the present study affect the height of midgut digestive cells. However, such reduction did not occur, probably because of the low-test concentrations. Although there were differences in digestive cell ultrastructure, ingestion of GBH impaired midgut digestive cell cohesion by disorganizing the smooth septate junctions between cells, which may probably be caused by the adjuvant "polyethoxylated tallow amine" present in the GBH. Previous studies demonstrated that GBH increase bees' sensibility to intestine infections, based on the present results we hypothesized that the loss of cell cohesion in the midgut epithelium favors pathogenic microbial infections and harms food absorption, increasing bees' mortality.

Fipronil exposure compromises respiration and damages the Malpighian tubules of the stingless bee Partamona helleri Friese (Hymenoptera: Apidae)

Fipronil has been widely used in agriculture and forestry in Brazil to control several pests. However, this insecticide may be hazardous to non-target organisms, including stingless bees, which are essential pollinators of crops and natural environments. Here, we investigated the effect of 24-h acute oral exposure to LC₅₀ of fipronil on the Malpighian tubules of the stingless bee Partamona helleri (Friese). Insecticide exposure decreases the respiration rate of forager bees, and the Malpighian tubules are severely affected, as shown by the epithelial architecture disorganization, loss of cytoplasmic content, degradation of the brush border, and nuclear pyknosis. In addition, fipronil ingestion increases the number of Malpighian cells positive for peroxidase, LC3, cleaved caspase-3, and JNK. However, Notch and ERK1/2-positive cells decrease in the exposed bees. These changes in the signaling proteins indicate an increase in oxidative stress, autophagy and apoptosis, and impairment of cell recovery. Overall, our results demonstrate the toxicological effects of fipronil on a stingless bee, which compromises the physiology of this important pollinator.

Biopesticides and insect pollinators: Detrimental effects, outdated guidelines, and future directions

As synthetic pesticides play a major role in pollinator decline worldwide, biopesticides have been gaining increased attention to develop more sustainable methods for pest management in agriculture. These biocontrol agents are usually considered as safe for non-target species, such as pollinators. Unfortunately, when it comes to non-target insects, only the acute or chronic effects on survival following exposure to biopesticides are tested. Although international boards have highlighted the need to include also behavioral and morphophysiological traits when assessing risks of plant protection products on pollinators, no substantial concerns have been raised about the risks associated with sublethal exposure to these substances. Here, we provide a comprehensive review of the studies investigating the potential adverse effects of biopesticides on different taxa of pollinators (bees, butterflies, moths, beetles, flies, and wasps). We highlight the fragmentary knowledge on this topic and the lack of a systematic investigation of these negative effects of biopesticides on insect pollinators. We show that all the major classes of biopesticides, besides their direct toxicity, can also cause a plethora of more subtle detrimental effects in both solitary and social species of pollinators. Although research in this field is growing, the current risk assesment approach does not suffice to properly assess all the potential side-effects that these agents of control may have on pollinating insects. Given the urgent need for a sustainable agriculture and wildlife protection, it appears compelling that these so far neglected detrimental effects should be thoroughly assessed before allegedly safe biopesticides can be used in the field and, in this view, we provide a perspective for future directions.

Microbial polyketides and their roles in insect virulence: from genomics to biological functions

Covering: May 1966 up to January 2022Entomopathogenic microorganisms have potential for biological control of insect pests. Their main secondary metabolites include polyketides, nonribosomal peptides, and polyketide-nonribosomal peptide (PK-NRP) hybrids. Among these secondary metabolites, polyketides have mainly been studied for structural identification, pathway engineering, and for their contributions to medicine. However, little is known about the function of polyketides in insect virulence. This review focuses on the role of bacterial and fungal polyketides, as well as PK-NRP hybrids in insect infection and killing. We also discuss gene distribution and evolutional relationships among different microbial species. Further, the role of microbial polyketides and the hybrids in modulating insect-microbial symbiosis is also explored. Understanding the mechanisms of polyketides in insect pathogenesis, how compounds moderate the host-fungus interaction, and the distribution of PKS genes across different fungi and bacteria will facilitate the discovery and development of novel polyketide-derived bio-insecticides.

A TetR family transcriptional regulator, SP_2854 can affect the butenyl-spinosyn biosynthesis by regulating glucose metabolism in Saccharopolyspora pogona

Background

Butenyl-spinosyn produced by Saccharopolyspora pogona exhibits strong insecticidal activity and a broad pesticidal spectrum. Currently, important functional genes involve in butenyl-spinosyn biosynthesis remain unknown, which leads to difficulty in efficiently understanding its regulatory mechanism, and improving its production by metabolic engineering.

Results

Here, we identified a TetR family transcriptional regulator, SP_2854, that can positively regulate butenyl-spinosyn biosynthesis and affect strain growth, glucose consumption, and mycelial morphology in S. pogona. Using targeted metabolomic analyses, we found that SP_2854 overexpression enhanced glucose metabolism, while SP_2854 deletion had the opposite effect. To decipher the overproduction mechanism in detail, comparative proteomic analysis was carried out in the SP-2854 overexpressing mutant and the original strain, and we found that SP_2854 overexpression promoted the expression of proteins involved in glucose metabolism.

Conclusion

Our findings suggest that SP_2854 can affect strain growth and development and butenyl-spinosyn biosynthesis in S. pogona by controlling glucose metabolism. The strategy reported here will be valuable in paving the way for genetic engineering of regulatory elements in actinomycetes to improve important natural products production.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12934-022-01808-2.

Pesticide-induced disturbances of bee gut microbiotas

Social bee gut microbiotas play key roles in host health and performance. Worryingly, a growing body of literature shows that pesticide exposure can disturb these microbiotas. Most studies examine changes in taxonomic composition in Western honey bee (Apis mellifera) gut microbiotas caused by insecticide exposure. Core bee gut microbiota taxa shift in abundance after exposure but are rarely eliminated, with declines in Bifidobacteriales and Lactobacillus near melliventris abundance being the most common shifts. Pesticide concentration, exposure duration, season and concurrent stressors all influence whether and how bee gut microbiotas are disturbed. Also, the mechanism of disturbance-i.e. whether a pesticide directly affects microbial growth or indirectly affects the microbiota by altering host health-likely affects disturbance consistency. Despite growing interest in this topic, important questions remain unanswered. Specifically, metabolic shifts in bee gut microbiotas remain largely uninvestigated, as do effects of pesticide-disturbed gut microbiotas on bee host performance. Furthermore, few bee species have been studied other than A. mellifera, and few herbicides and fungicides have been examined. We call for these knowledge gaps to be addressed so that we may obtain a comprehensive picture of how pesticides alter bee gut microbiotas, and of the functional consequences of these changes.

Impact of copper sulfate on survival, behavior, midgut morphology, and antioxidant activity of Partamona helleri (Apidae: Meliponini)

Copper sulfate (CuSO₄) is widely used in agriculture as a pesticide and foliar fertilizer. However, the possible environmental risks associated with CuSO₄ use, particularly related to pollinating insects, have been poorly studied. In this study, we evaluated both lethal and sublethal effects of CuSO₄ on the stingless bee Partamona helleri. Foragers were orally exposed to five concentrations of CuSO₄ (5000, 1666.7, 554.2, 183.4, 58.4 μg mL^-1), and the concentration killing 50% (LC₅₀) was estimated. This concentration (142.95 μg mL^-1) was subsequently used in behavioral, midgut morphology, and antioxidant activity analyses. Bee mortality increased with the ingestion of increasing concentrations of CuSO₄. Ingestion at the estimated LC₅₀ resulted in altered walking behavior and damage to the midgut epithelium and peritrophic matrix of bees. Furthermore, the LC₅₀ increased the catalase or superoxide dismutase activities and levels of the lipid peroxidation biomarker malondialdehyde. Furthermore, the in situ detection of caspase-3 and LC3, proteins related to apoptosis and autophagy, respectively, revealed that these processes are intensified in the midgut of treated bees. These data show that the ingestion of CuSO₄ can have considerable sublethal effects on the walking behavior and midgut of stingless bees, and therefore could pose potential risks to pollinators including native bees. Graphical abstract.

Deletion of a hybrid NRPS-T1PKS biosynthetic gene cluster via Latour gene knockout system in Saccharopolyspora pogona and its effect on butenyl-spinosyn biosynthesis and growth development

Butenyl-spinosyn, a promising biopesticide produced by Saccharopolyspora pogona, exhibits stronger insecticidal activity and a broader pesticidal spectrum. However, its titre in the wild-type S. pogona strain is too low to meet the industrial production requirements. Deletion of non-target natural product biosynthetic gene clusters resident in the genome of S. pogona could reduce the consumption of synthetic precursors, thereby promoting the biosynthesis of butenyl-spinosyn. However, it has always been a challenge for scientists to genetically engineer S. pogona. In this study, the Latour gene knockout system (linear DNA fragment recombineering system) was established in S. pogona. Using the Latour system, a hybrid NRPS-T1PKS cluster (˜20 kb) which was responsible for phthoxazolin biosynthesis was efficiently deleted in S. pogona. The resultant mutant S. pogona-Δura4-Δc14 exhibited an extended logarithmic phase, increased biomass and a lower glucose consumption rate. Importantly, the production of butenyl-spinosyn in S. pogona-Δura4-Δc14 was increased by 4.72-fold compared with that in the wild-type strain. qRT-PCR analysis revealed that phthoxazolin biosynthetic gene cluster deletion could promote the expression of the butenyl-spinosyn biosynthetic gene cluster. Furthermore, a TetR family transcriptional regulatory gene that could regulate the butenyl-spinosyn biosynthesis has been identified from the phthoxazolin biosynthetic gene cluster. Because dozens of natural product biosynthetic gene clusters exist in the genome of S. pogona, the strategy reported here will be used to further promote the production of butenyl-spinosyn by deleting other secondary metabolite synthetic gene clusters.

Comparative Proteomics Reveals the Effect of the Transcriptional Regulator Sp13016 on Butenyl-Spinosyn Biosynthesis in Saccharopolyspora pogona

Butenyl-spinosyn is a highly effective and broad-spectrum biopesticide produced by Saccharopolyspora pogona. However, the yield of this compound is difficult to increase because the regulatory mechanism of secondary metabolism is still unknown. Here, the transcriptional regulator Sp13016 was discovered to be highly associated with butenyl-spinosyn synthesis and bacterial growth. Overexpression of sp13016 improved butenyl-spinosyn production to a level that was 2.84-fold that of the original strain, while deletion of sp13016 resulted in a significant decrease in yield and growth inhibition. Comparative proteomics revealed that these phenotypic changes were attributed to the influence of Sp13016 on the central carbon metabolism pathway to regulate the supply of precursors. Our research helps to reveal the regulatory mechanism of butenyl-spinosyn biosynthesis and provides a reference for increasing the yield of natural products of Actinomycetes.

Bacterioferritin: a key iron storage modulator that affects strain growth and butenyl-spinosyn biosynthesis in Saccharopolyspora pogona

Background

Butenyl-spinosyn, produced by Saccharopolyspora pogona, is a promising biopesticide due to excellent insecticidal activity and broad pesticidal spectrum. Bacterioferritin (Bfr, encoded by bfr) regulates the storage and utilization of iron, which is essential for the growth and metabolism of microorganisms. However, the effect of Bfr on the growth and butenyl-spinosyn biosynthesis in S. pogona has not been explored.

Results

Here, we found that the storage of intracellular iron influenced butenyl-spinosyn biosynthesis and the stress resistance of S. pogona, which was regulated by Bfr. The overexpression of bfr increased the production of butenyl-spinosyn by 3.14-fold and enhanced the tolerance of S. pogona to iron toxicity and oxidative damage, while the knockout of bfr had the opposite effects. Based on the quantitative proteomics analysis and experimental verification, the inner mechanism of these phenomena was explored. Overexpression of bfr enhanced the iron storage capacity of the strain, which activated polyketide synthase genes and enhanced the supply of acyl-CoA precursors to improve butenyl-spinosyn biosynthesis. In addition, it induced the oxidative stress response to improve the stress resistance of S. pogona.

Conclusion

Our work reveals the role of Bfr in increasing the yield of butenyl-spinosyn and enhancing the stress resistance of S. pogona, and provides insights into its enhancement on secondary metabolism, which provides a reference for optimizing the production of secondary metabolites in actinomycetes.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12934-021-01651-x.

Acute exposure to fipronil induces oxidative stress, apoptosis and impairs epithelial homeostasis in the midgut of the stingless bee Partamona helleri Friese (Hymenoptera: Apidae)

Partamona helleri is an important pollinator in natural and agricultural ecosystems in the neotropics. However, the foraging activity of this bee increases its risk of exposure to pesticides, which may affect both the individuals and the colony. Thus, this study aims to evaluate the side effects of LC₅₀ of fipronil (0.28 ng a.i. μL^-1) on the midgut morphology, antioxidant activity and some pathways of cell death, proliferation and differentiation in workers of P. helleri, after 24 h of oral exposure. Fipronil caused morphological alterations in the midgut of the bees. The activities of the detoxification enzymes superoxide dismutase, catalase and glutathione S-transferase increased after exposure, which suggests the occurrence of a detoxification mechanism. Furthermore, exposure to fipronil changed the number of positive cells for signaling-pathway proteins in the midgut of bees, which indicates the induction of cell death by the apoptotic pathway and impairment of the midgut epithelial regeneration. These results demonstrate that fipronil may negatively affect the morphology and physiology of the midgut of the stingless bee P. helleri and impose a threat to the survival of non-target organisms.

A mixture containing the herbicides Mesotrione and Atrazine imposes toxicological risks on workers of Partamona helleri

A mixture of Mesotrione and Atrazine (Calaris®) has been reported as an improvement of the atrazine herbicides, which are agrochemicals used for weed control. However, its possible harmful effects on non-target organisms, including pollinators, needs to be better understood. In this work, the effects of the mix of herbicides on food consumption, behaviour (walking distance, and meandering), and the morphology of the midgut of the stingless bee Partamona helleri were studied. Foragers were orally exposed to different concentrations of the mix. The concentrations leading to 10% and 50% mortality (LC₁₀ and LC₅₀, respectively) were estimated and used in the analysis of behaviour and morphology. The ingestion of contaminated diets (50% aqueous sucrose solution + mix) led to a reduction in food consumption by the bees when compared to the control, bees fed a non-contaminated diet (sucrose solution). Ingestion of the LC₅₀ diet reduced locomotor activity, increased meandering, induced the degradation of the epithelium and peritrophic matrix, and also changed the number of cells positive for signalling-pathway proteins in the midgut. These results show the potential toxicological effects and environmental impacts of the mix of herbicides in beneficial insects, including a native bee.

Identification of a TetR family regulator and a polyketide synthase gene cluster involved in growth development and butenyl-spinosyn biosynthesis of Saccharopolyspora pogona

Butenyl-spinosyn produced by Saccharopolyspora pogona exhibits strong insecticidal activity and broad pesticidal spectrum. However, its synthetic level was low in the wild-type strain. At present, important functional genes involved in butenyl-spinosyn biosynthesis remain unknown, which leads to difficulty in efficiently editing its genome to improve the butenyl-spinosyn yield. To accelerate the genetic modification of S. pogona, we conducted comparative proteomics analysis to screen differentially expressed proteins related to butenyl-spinosyn biosynthesis. A TetR family regulatory protein was selected from the 289 differentially expressed proteins, and its encoding gene (SP_1288) was successfully deleted by CRISPR/Cas9 system. We further deleted a 32-kb polyketide synthase gene cluster (cluster 28) to reduce the competition for precursors. Phenotypic analysis revealed that the deletion of the SP_1288 and cluster 28 resulted in a 3.10-fold increase and a 35.4% decrease in the butenyl-spinosyn levels compared with the wild-type strain, respectively. The deletion of cluster 28 affected the cell growth, glucose consumption, mycelium morphology, and sporulation by controlling the expression of ptsH, ptsI, amfC, and other genes related to sporulation, whereas SP_1288 did not. These findings confirmed not only that the CRISPR/Cas9 system can be applied to the S. pogona genome editing but also that SP_1288 and cluster 28 are closely related to the butenyl-spinosyn biosynthesis and growth development of S. pogona. The strategy reported here will be useful to reveal the regulatory mechanism of butenyl-spinosyn and improve antibiotic production in other actinomycetes. KEY POINTS: • SP_1288 deletion can significantly promote the butenyl-spinosyn biosynthesis. • Cluster 28 deletion showed pleiotropic effects on S. pogona. • SP_1288 and cluster 28 were deleted by CRISPR/Cas9 system in S. pogona.

Global trends in pesticides: A looming threat and viable alternatives

Pesticides are widely used chemical compounds in agriculture to destroy insects, pests and weeds. In modern era, they form an indispensable part of agricultural and health practices. Globally, nearly 3 billion kg of pesticides are used every year with a budget of ~40 billion USD. This extensive usage has increased the crop yield as well as led to significant reduction in harvest losses and thereby, enhanced food availability. On the other hand, indiscriminate usage of these chemicals has led to several environmental implications and caused adverse effects on human health. Epidemiological evidences have revealed the harmful effects of pesticides exposure on various organs including liver, brain, lungs and colon. Recent investigations have shown that pesticides can also lead to fatal consequences such as cancer among individuals. These chemicals enter ecosystem, thus hampering the sensitive environmental equilibrium through bio-accumulation. Due to their non-biodegradable nature, they can persist in nature for years and are regarded as potent biohazard. Worldwide, very few surveillance methods have been considered, which can bring awareness among the individuals, therefore the present review is an attempt to delineate consequences induced by various types of pesticide exposure on the environment. Further, the prospective of biopesticides use could facilitate the increase of crop production without compromising human health.

A Spinosad-Based Formulation Reduces the Survival and Alters the Behavior of the Stingless Bee Plebeia lucii

The decline in bee populations worldwide has been associated with the use of pesticides in crop systems where these insects forage. The use of biopesticides, like spinosad, is preferred as an alternative method to control pests, because it is considered safer to non-target insects. In this study, we evaluated the lethal and sublethal effects of the spinosad-based formulation Tracer® on foragers of the stingless bee Plebeia lucii Moure (Apidae: Meliponini). Groups of bees were fed a pure diet (negative control) or a diet at different concentrations of spinosad. Positive control groups consisted of bees orally exposed to a diet with the neonicotinoid imidacloprid. Next, flight behavior, body mass, and respiration rate were evaluated in surviving bees. The results showed that bees´ survival was reduced by all concentrations of spinosad, when compared with the negative control. Bee locomotion-walking and flight-was reduced in accordance with the increase in spinosad concentrations; however, body mass and respiration rate were not altered. Our results show that the use of Tracer® in ecosystems visited by P. lucii can reduce forager bee survival and reduce their locomotion, generating a negative impact on pollination services provided by these bees.

Toxicological assessments of agrochemical effects on stingless bees (Apidae, Meliponini)

Bee pollination is crucial for ecosystem maintenance and crop production. The ubiquity of bee pollinators in agricultural landscapes frequently results in their exposure to agrochemicals, which has been associated with their decline. Stingless bees are wild pollinators restricted to the Pantropical region, and like honey bees, are suffering colony losses. However, stingless bees and honey bees do not show the same behaviors, therefore, methods used for risk assessment of honey bees cannot be utilized on stingless bees. Herein, we describe protocols to standardize methods that allow for the exploration of lethal and sublethal effects of agrochemicals via acute and chronic exposure of stingless bees. The in vitro rearing used for chronic exposure from the egg to the adult stage proved to be effective in obtaining relevant screenings. In addition, we performed a meta-analysis and summarized the results of toxicological studies conducted with the protocols described. The meta-analyses indicated a reduction in survival under acute and chronic exposures to agrochemicals, and revealed that our protocols for toxicological assessments did not have publication bias for either acute or chronic exposure. These findings proved that these standardized protocols are reliable for toxicological research on stingless bee.

Behavior and gut bacteria of Partamona helleri under sublethal exposure to a bioinsecticide and a leaf fertilizer

The exposure of bees to agrochemicals during foraging and feeding has been associated with their population decline. Sublethal exposure to agrochemicals can affect behavior and the microbiota. Gut microbiota is associated with insect nutritional health, immunocompetence, and is essential for neutralizing the damage caused by pathogens and xenobiotics. Research on the effect of the bioinsecticides and fertilizers on the microbiota of bees remains neglected. In this study, we assessed the sublethal effect of both bioinsecticide spinosad and the fertilizer copper sulfate (CuSO₄) on the behavior and gut microbiota in forager adults of the stingless bee Partamona helleri (Friese), which is an important pollinator in the Neotropical region. Behavioral assays and gut microbiota profiles were assessed on bees orally exposed to estimated LC₅ values for spinosad and CuSO₄. The microbiota were characterized through 16S rRNA gene target sequencing. Acute and oral sublethal exposure to spinosad and CuSO₄ did not affect the overall activity, flight take-off, and food consumption. However, CuSO₄ decreased bee respiration rate and copper accumulated in exposed bees. Exposure to spinosad increased the proportional abundance of the genus Gilliamella, but CuSO₄ did not alter the composition of the gut microbiota. In conclusion, sublethal exposure to CuSO₄ induces changes in respiration, and spinosad changes the abundance of gut microorganisms of P. helleri.

Spinosad-mediated effects in the post-embryonic development of Partamona helleri (Hymenoptera: Apidae: Meliponini)

The use of insecticides based on metabolites found in live organisms, such as the insecticide spinosad, has been an option for the control of agricultural pests because of the allegedly low toxicological risk for nontarget arthropods, such as stingless bees. In the current study, we evaluate the effects of chronic oral exposure to spinosad during the larval phase on survival, developmental time, body mass, midgut epithelial remodeling, and the peritrophic matrix (PM) of Partamona helleri stingless bee workers. Worker larvae that were raised in the laboratory were orally exposed to different concentrations (0, 6.53, 13.06, 32.64, and 3,264 ng. a.i. bee^-1) of spinosad (formulation), and the resulting survival, developmental time, and body mass were studied. The concentration of spinosad recommended for use in the field (3,264 ng. a.i. bee^-1) reduced the survival of workers during development. Also, sublethal concentrations of spinosad delayed the development and caused morphological changes in the midgut epithelium. Finally, the chronic exposure of larvae to 32.64 ng. a.i. bee^-1 spinosad also altered the remodeling of the midgut during metamorphosis and affected the organization of the PM of larvae, pupae, and adults. Our data suggest possible environmental risks for using spinosad in cultures that are naturally pollinated by stingless bees.