Changes in Microbiome Confer Multigenerational Host Resistance after Sub-toxic Pesticide Exposure

Acute toxicity effects of pesticides on beneficial organisms - Dispelling myths for a more sustainable use of chemicals in agricultural environments

Agricultural practitioners, researchers and policymakers are increasingly advocating for integrated pest management (IPM) to reduce pesticide use while preserving crop productivity and profitability. Using selective pesticides, putatively designed to act on pests while minimising impacts on off-target organisms, is one such option - yet evidence of whether these chemicals control pests without adversely affecting natural enemies and other beneficial species (henceforth beneficials) remains scarce. At present, the selection of pesticides compatible with IPM often considers a single (or a limited number of) widely distributed beneficial species, without considering undesired effects on co-occurring beneficials. In this study, we conducted standardised laboratory bioassays to assess the acute toxicity effects of 20 chemicals on 15 beneficial species at multiple exposure timepoints, with the specific aims to: (1) identify common and diverging patterns in acute toxicity responses of tested beneficials; (2) determine if the effect of pesticides on beetles, wasps and mites is consistent across species within these groups; and (3) assess the impact of mortality assessment timepoints on International Organisation for Biological Control (IOBC) toxicity classifications. Our work demonstrates that in most cases, chemical toxicities cannot be generalised across a range of beneficial insects and mites providing biological control, a finding that was found even when comparing impacts among closely related species of beetles, wasps and mites. Additionally, we show that toxicity impacts increase with exposure length, pointing to limitations of IOBC protocols. This work challenges the notion that chemical toxicities can be adequately tested on a limited number of 'representative' species; instead, it highlights the need for careful consideration and testing on a range of regionally and seasonally relevant beneficial species.

Effects of abamectin nanocapsules on bees through host physiology, immune function, and gut microbiome

Pesticide usage is a common practice to increase crop yields. Nevertheless, the existence of pesticide residues in the surrounding environment presents a significant hazard to pollinators, specifically the potential undisclosed dangers related to emerging nanopesticides. This study examines the impact of abamectin nanocapsules (AbaNCs), created through electrostatic self-assembly, as an insecticide on honey bees. It was determined that AbaNCs upregulated detoxification genes, including CYP450, as well as antioxidant and immune genes in honey bees. Furthermore, AbaNCs affected the activity of crucial enzymes such as superoxide dismutase (SOD). Although no apparent damage was observed in bee gut tissue, AbaNCs significantly decreased digestive enzyme activity. Microbiome sequencing revealed that AbaNCs disrupted gut microbiome, resulting in a reduction of beneficial bacteria such as Bifidobacterium and Lactobacillus. Additionally, these changes in the gut microbiome were associated with decreased activity of digestive enzymes, including lipase. This study enhances our understanding of the impact of nanopesticides on pollinating insects. Through the revelation of the consequences arising from the utilization of abamectin nanocapsules, we have identified potential stress factors faced by these pollinators, enabling the implementation of improved protective measures.

Pesticide use and inflammatory bowel disease in licensed pesticide applicators and spouses in the Agricultural Health Study

BACKGROUND

Pesticide exposure has been linked to some autoimmune diseases and colorectal cancer, possibly via alteration of gut microbiota or other mechanisms. While pesticides have been linked to gut dysbiosis and inflammation in animal models, few epidemiologic studies have examined pesticides in relation to inflammatory bowel disease (IBD).

OBJECTIVES

We evaluated use of pesticides and incident IBD in 68,480 eligible pesticide applicators and spouses enrolled in the Agricultural Health Study.

METHODS

Self-reported IBD cases were identified from follow-up questionnaires between enrollment (1993-1997) and 2022. We evaluated IBD incidence in relation to self-reported ever use of 50 pesticides among applicators and spouses. We also explored associations with intensity-weighted lifetime days (IWLD) of pesticide use among male applicators. Covariate-adjusted hazard ratios (HR) and 95% confidence intervals (CI) were calculated using Cox regression.

RESULTS

We identified 454 IBD cases, including 227 among male applicators. In analyses with applicators and spouses combined, associations were positive (HR > 1.2) for ever vs. never use of five organochlorine insecticides, three organophosphate insecticides, one fungicide, and five herbicides. HRs were highest for dieldrin (HR = 1.59, 95%CI: 1.03, 2.44), toxaphene (HR = 1.61, 95%CI: 1.17, 2.21), parathion (HR = 1.42, 95%CI: 1.03, 1.95), and terbufos (HR = 1.53, 95%CI: 1.19, 1.96). We had limited power in many IWLD of pesticide use analyses and did not find clear evidence of exposure-response trends; however, we observed elevated HRs in all tertiles of IWLD use of terbufos compared to never use (T1 vs. never use HR = 1.52, 95%CI: 1.03, 2.24; T2 vs. never use HR = 1.53, 95%CI: 1.04, 2.26; T3 vs. never use HR = 1.51, 95%CI: 1.03, 2.23).

CONCLUSIONS

Exposure to specific pesticides was associated with elevated hazards of IBD. These findings may have public health importance given the widespread use of pesticides and the limited number of known modifiable environmental risk factors for IBD.

Sphingomonas bacteria could serve as an early bioindicator for the development of chlorantraniliprole resistance in Spodoptera frugiperda

The fall armyworm (Spodoptera frugiperda) was found to have invaded China in December 2018, and in just one year, crops in 26 provinces were heavily affected. Currently, the most effective method for emergency control of fulminant pests is to use of chemical pesticides. Recently, most fall armyworm populations in China were begining to exhibite low level resistance to chlorantraniliprole. At present, it is not possible to sensitively reflect the low level resistance of S. frugiperda by detecting target mutation and detoxification enzyme activity. In this study we found that 12 successive generations of screening with chlorantraniliprole caused S. frugiperda to develop low level resistance to this insecticide, and this phenotype was not attribute to genetic mutations in S. frugiperda, but rather to a marked increase in the relative amount of the symbiotic bacteria Sphingomonas. Using FISH and qPCR assays, we determined the amount of Sphingomonas in the gut of S. frugiperda and found Sphingomonas accumulation to be highest in the 3rd-instar larvae. Additionally, Sphingomonas was observed to provide a protective effect to against chlorantraniliprole stress to S. frugiperda. With the increase of the resistance to chlorantraniliprole, the abundance of bacteria also increased, we propose Sphingomonas monitoring could be adapted into an early warning index for the development of chlorantraniliprole resistance in S. frugiperda populations, such that timely measures can be taken to delay or prevent the widespread propagation of resistance to this highly useful agricultural chemical in S. frugiperda field populations.

Seed microbiome-mediated herbicide resistance evolution in weeds

See also the Commentary on this article by Zhang et al., 242: 327–330.

Snail microbiota and snail-schistosome interactions: axenic and gnotobiotic technologies

The microbiota in the intermediate snail hosts of human schistosomes can significantly affect host biology. For decades, researchers have developed axenic snails to manipulate the symbiotic microbiota. This review summarizes the characteristics of symbiotic microbes in intermediate snail hosts and describes their interactions with snails, affecting snail growth, development, and parasite transmission ability. We focus on advances in axenic and gnotobiotic technologies for studying snail-microbe interactions and exploring the role of microbiota in snail susceptibility to Schistosoma infection. We discuss the challenges related to axenic and gnotobiotic snails, possible solutions to address these challenges, and future research directions to deepen our understanding of snail-microbiota interactions, with the aim to develop microbiota-based strategies for controlling snail populations and reducing their competence in transmitting parasites.

The symbiont Wolbachia alleviates pesticide susceptibility in the two-spotted spider mite Tetranychus urticae through enhanced host detoxification pathways

The two-spotted spider mite (Tetranychus urticae) is one of the most well-known pesticide-resistant agricultural pests, with resistance often attributed to changes such as target-site mutations and detoxification activation. Recent studies show that pesticide resistance can also be influenced by symbionts, but their involvement in this process in spider mites remains uncertain. Here, we found that infection with Wolbachia, a well-known bacterial reproductive manipulator, significantly increased mite survival after exposure to the insecticides abamectin, cyflumetofen, and pyridaben. Wolbachia-infected (WI) mites showed higher expression of detoxification genes such as P450, glutathione-S-transferase (GST), ABC transporters, and carboxyl/cholinesterases. RNA interference experiments confirmed the role of the two above-mentioned detoxification genes, TuCYP392D2 and TuGSTd05, in pesticide resistance. Increased GST activities were also observed in abamectin-treated WI mites. In addition, when wild populations were treated with abamectin, WI mites generally showed better survival than uninfected mites. However, genetically homogeneous mites with different Wolbachia strains showed similar survival. Finally, abamectin treatment increased Wolbachia abundance without altering the mite's bacterial community. This finding highlights the role of Wolbachia in orchestrating pesticide resistance by modulating host detoxification. By unraveling the intricate interplay between symbionts and pesticide resistance, our study lays the groundwork for pioneering strategies to combat agricultural pests.

A broad-taxa approach as an important concept in ecotoxicological studies and pollution monitoring

Aquatic invertebrates play a pivotal role in (eco)toxicological assessments because they offer ethical, cost-effective and repeatable testing options. Additionally, their significance in the food chain and their ability to represent diverse aquatic ecosystems make them valuable subjects for (eco)toxicological studies. To ensure consistency and comparability across studies, international (eco)toxicology guidelines have been used to establish standardised methods and protocols for data collection, analysis and interpretation. However, the current standardised protocols primarily focus on a limited number of aquatic invertebrate species, mainly from Arthropoda, Mollusca and Annelida. These protocols are suitable for basic toxicity screening, effectively assessing the immediate and severe effects of toxic substances on organisms. For more comprehensive and ecologically relevant assessments, particularly those addressing long-term effects and ecosystem-wide impacts, we recommended the use of a broader diversity of species, since the present choice of taxa exacerbates the limited scope of basic ecotoxicological studies. This review provides a comprehensive overview of (eco)toxicological studies, focusing on major aquatic invertebrate taxa and how they are used to assess the impact of chemicals in diverse aquatic environments. The present work supports the use of a broad-taxa approach in basic environmental assessments, as it better represents the natural populations inhabiting various ecosystems. Advances in omics and other biochemical and computational techniques make the broad-taxa approach more feasible, enabling mechanistic studies on non-model organisms. By combining these approaches with in vitro techniques together with the broad-taxa approach, researchers can gain insights into less-explored impacts of pollution, such as changes in population diversity, the development of tolerance and transgenerational inheritance of pollution responses, the impact on organism phenotypic plasticity, biological invasion outcomes, social behaviour changes, metabolome changes, regeneration phenomena, disease susceptibility and tissue pathologies. This review also emphasises the need for harmonised data-reporting standards and minimum annotation checklists to ensure that research results are findable, accessible, interoperable and reusable (FAIR), maximising the use and reusability of data. The ultimate goal is to encourage integrated and holistic problem-focused collaboration between diverse scientific disciplines, international standardisation organisations and decision-making bodies, with a focus on transdisciplinary knowledge co-production for the One-Health approach.

Serratia marcescens induces apoptosis in Diaphorina citri gut cells via reactive oxygen species-mediated oxidative stress

BACKGROUND

Asian citrus psyllid, Diaphorina citri, is a notorious pest in the citrus industry because it transmits Candidatus Liberibacter asiaticus, which causes an uncurable, devastating disease in citrus worldwide. Serratia marcescens is widely distributed in various environments that exhibits toxic effects to many insects. To develop strategies for enhancing the efficiency of pathogen-induced host mortality, a better understanding of the toxicity mechanism of Serratia marcescens on Diaphorina citri is critical.

RESULTS

Serratia marcescens KH-001 successfully colonized Diaphorina citri gut by feeding artificial diets, resulting in the damage of cells including nucleus, mitochondria, vesicles, and microvilli. Oral ingestion of Serratia marcescens KH-001 strongly induced apoptosis in gut cells by enhancing levels of Cyt c, p53 and caspase-1 and decreasing levels of inhibitors of apoptosis (IAP) and Bax inhibitor-1 (BI-1). The expression of dual oxidase (Duox) and nitric oxide synthase (Nos) was up-regulated by Serratia marcescens KH-001, which increased hydrogen peroxide (H2 O2 ) levels in the gut. Injection of abdomen of Diaphorina citri with H2 O2 accelerated the death of the adults and induced apoptosis in the gut cells by activating Cyt c, p53 and caspase-1 and suppressing IAP and BI-1. Pretreatment of infected Diaphorina citri with vitamin c (Vc) increased the adult survival and diminished the apoptosis-inducing effect.

CONCLUSIONS

The colonization of Serratia marcescens KH-001 in the guts of Diaphorina citri increased H2 O2 accumulation, leading to severe changes and apoptosis in intestinal cells, which enhanced a higher mortality level of D. citr. This study identifies the underlying virulence mechanism of Serratia marcescens KH-001 on Diaphorina citri that contributes to a widespread application in the integrated management of citrus psyllid. © 2023 Society of Chemical Industry.

Genome sequence of Staphylococcus nepalensis ZZ-2023a, isolated from Nasonia vitripennis

We isolated a strain of Staphylococcus nepalensis from Nasonia vitripennis and presented the draft genome sequence of this strain. This research was conducted at the Institute of Zoology, Chinese Academy of Sciences (Beijing, China). The genome spans 2,910,033 bp, distributed over 144 contigs, with a G+C content of 33.33%.

Symbiotic bacteria confer insecticide resistance by metabolizing buprofezin in the brown planthopper, Nilaparvata lugens (Stål)

Buprofezin, a chitin synthesis inhibitor, is widely used to control several economically important insect crop pests. However, the overuse of buprofezin has led to the evolution of resistance and exposed off-target organisms present in agri-environments to this compound. As many as six different strains of bacteria isolated from these environments have been shown to degrade buprofezin. However, whether insects can acquire these buprofezin-degrading bacteria from soil and enhance their own resistance to buprofezin remains unknown. Here we show that field strains of the brown planthopper, Nilaparvata lugens, have acquired a symbiotic bacteria, occurring naturally in soil and water, that provides them with resistance to buprofezin. We isolated a symbiotic bacterium, Serratia marcescens (Bup_Serratia), from buprofezin-resistant N. lugens and showed it has the capacity to degrade buprofezin. Buprofezin-susceptible N. lugens inoculated with Bup_Serratia became resistant to buprofezin, while antibiotic-treated N. lugens became susceptible to this insecticide, confirming the important role of Bup_Serratia in resistance. Sequencing of the Bup_Serratia genome identified a suite of candidate genes involved in the degradation of buprofezin, that were upregulated upon exposure to buprofezin. Our findings demonstrate that S. marcescens, an opportunistic pathogen of humans, can metabolize the insecticide buprofezin and form a mutualistic relationship with N. lugens to enhance host resistance to buprofezin. These results provide new insight into the mechanisms underlying insecticide resistance and the interactions between bacteria, insects and insecticides in the environment. From an applied perspective they also have implications for the control of highly damaging crop pests.

A multi-study analysis of gut microbiome data from the blue mussel (Mytilus edulis) emphasises the impact of depuration on biological interpretation

The blue mussel (Mytilus edulis) is a suspension feeder which has been used in gut-microbiome surveys. Although raw 16S sequence data are often publicly available, unifying secondary analyses are lacking. The present work analysed raw data from seven projects conducted by one group over 7 years. Although each project had different motivations, experimental designs and conclusions, all selected samples were from the guts of M. edulis collected from a single location in Long Island Sound. The goal of this analysis was to determine which independent factors (e.g., collection date, depuration status) were responsible for governing composition and diversity in the gut microbiomes. Results indicated that whether mussels had undergone depuration, defined here as voidance of faeces in a controlled, no-food period, was the primary factor that governed gut microbiome composition. Gut microbiomes from non-depurated mussels were mixtures of resident and transient communities and were influenced by temporal factors. Resident communities from depurated mussels were influenced by the final food source and length of time host mussels were held under laboratory conditions. These findings reinforce the paradigm that gut microbiota are divided into resident and transient components and suggest that depuration status should be taken into consideration when designing and interpreting future experiments.

Effects of parasitism by a parasitoid wasp on the gut microbiota in a predaceous lady beetle host

BACKGROUND

The gut microbiota has an intimate relationship with insect hosts and this relationship can become complicated with parasitic organisms being involved with the host. To date there has been limited evidence for the relevance of parasitism of the host by parasitoids to host gut microbiota, especially in host insect predators. Here, our study examined gut microbiotas in larvae of the predaceous lady beetle, Coccinella septempunctata, in response to their parasitism by Homalotylus eytelweinii regarding the development progress of offspring parasitoids.

RESULTS

Overall 58.5% of gut bacterial operational taxonomic units (OTUs) in the parasitized lady beetle were different from those in the unparasitized host. The phylum Proteobacteria abundance increased while Firmicutes decreased in parasitized hosts compared to the unparasitized. The abundance of genus Aeribacillus decreased substantially in the parasitized lady beetle across all stages of the offspring development compared to the unparasitized host. The α-diversity of the gut microbiota in a parasitized lady beetle larva increased at the early stage of offspring parasitoids and then returned over the intermediate and later stages. Analyses of β-diversity indicated that the gut microbial community in a parasitized lady beetle was distinct from that in an unparasitized one and different between early or middle and late stages of offspring parasitoids in parasitized hosts.

CONCLUSION

Our results provide evidence for the relevance of the gut microbiota to interactions between a lady beetle host and its parasitoid. Our study provides a starting point for further investigations of the role the gut microbiota may play in host-parasitoid interactions. © 2023 Society of Chemical Industry.

Comparative Genomics of Pesticide-Degrading Enterococcus Symbionts of Spodoptera frugiperda (Lepidoptera: Noctuidae) Leads to the Identification of Two New Species and the Reappraisal of Insect-Associated Enterococcus Species

Enterococcus species have been described as core members of the microbial community of Spodoptera frugiperda (Lepidoptera: Noctuidae) and have been previously reported as insecticide degrading agents. This study aimed to investigate the molecular composition of these microbial symbionts of S. frugiperda to better understand their association with the host and their potential for insecticide metabolization. Through phenotypic assays and comparative genomic analyses of several pesticide-degrading Enterococcus isolated from the gut of S. frugiperda larvae, we identified two new species: Enterococcus entomosocium n. sp. and Enterococcus spodopteracolus n. sp. Their identities as new species were confirmed by whole genome alignment, utilizing cut-offs of 95-96% for the average nucleotide identity (ANI) and 70% for the digital DNA: DNA hybridization (dDDH) values. The systematic positioning of these new species within the genus Enterococcus was resolved using genome-based analysis, revealing Enterococcus casseliflavus as a sister group of E. entomosocium n. sp., and Enterococcus mundtii as a sister group of E. spodopteracolus n. sp. Comparative genomic analyses of several isolates of E. entomosocium n. sp. and E. spodopteracolus n. sp. provided a better assessment of the interactions established in the symbiotic association with S. frugiperda and led to the discovery of misidentified new species of Enterococcus associated with insects. Our analyses indicated that the potential of E. entomosocium n. sp. and E. spodopteracolus n. sp. to metabolize different pesticides arises from molecular mechanisms that result in rapid evolution of new phenotypes in response to environmental stressors, in this case, the pesticides their host insect is exposed to.

Response of the Propylea japonica Microbiota to Treatment with Cry1B Protein

Propylea japonica (Thunberg) (Coleoptera: Coccinellidae) is a dominant natural enemy of insect pests in farmland ecosystems. It also serves as an important non-target insect for environmental safety evaluations of transgenic crops. Widespread planting of transgenic crops may result in direct or indirect exposure of P. japonica to recombinant Bacillus thuringiensis (Bt) protein, which may in turn affect the biological performance of this natural enemy by affecting the P. japonica microflora. However, the effects of Bt proteins (such as Cry1B) on the P. japonica microbiota are currently unclear. Here, we used a high-throughput sequencing method to investigate differences in the P. japonica microbiota resulting from treatment with Cry1B compared to a sucrose control. The results demonstrated that the P. japonica microbiome was dominated by Firmicutes at the phylum level and by Staphylococcus at the genus level. Within-sample (α) diversity indices demonstrated a high degree of consistency between the microbial communities of P. japonica treated with the sucrose control and those treated with 0.25 or 0.5 mg/mL Cry1B. Furthermore, there were no significant differences in the abundance of any taxa after treatment with 0.25 mg/mL Cry1B for 24 or 48 h, and treatment with 0.5 mg/mL Cry1B for 24 or 48 h led to changes only in Staphylococcus, a member of the phylum Firmicutes. Treatment with a high Cry1B concentration (1.0 mg/mL) for 24 or 48 h caused significant changes in the abundance of specific taxa (e.g., Gemmatimonades, Patescibacteria, Thauera, and Microbacterium). However, compared with the control, most taxa remained unchanged. The statistically significant differences may have been due to the stimulatory effects of treatment with a high concentration of Cry1B. Overall, the results showed that Cry1B protein could alter endophytic bacterial community abundance, but not composition, in P. japonica. The effects of Bt proteins on endophytes and other parameters in non-target insects require further study. This study provides data support for the safety evaluation of transgenic plants.

Homeostatic Regulation of the Duox-ROS Defense System: Revelations Based on the Diversity of Gut Bacteria in Silkworms (Bombyx mori)

The Duox-ROS defense system plays an important role in insect intestinal immunity. To investigate the role of intestinal microbiota in Duox-ROS regulation herein, 16S rRNA sequencing technology was utilized to compare the characteristics of bacterial populations in the midgut of silkworm after different time-periods of treatment with three feeding methods: 1-4 instars artificial diet (AD), 1-4 instars mulberry leaf (ML) and 1-3 instars artificial diet + 4 instar mulberry leaf (TM). The results revealed simple intestinal microbiota in the AD group whilst microbiota were abundant and variable in the ML and TM silkworms. By analyzing the relationship among intestinal pH, reactive oxygen species (ROS) content and microorganism composition, it was identified that an acidic intestinal environment inhibited the growth of intestinal microbiota of silkworms, observed concurrently with low ROS content and a high activity of antioxidant enzymes (SOD, TPX, CAT). Gene expression associated with the Duox-ROS defense system was detected using RT-qPCR and identified to be low in the AD group and significantly higher in the TM group of silkworms. This study provides a new reference for the future improvement of the artificial diet feeding of silkworm and a systematic indicator for the further study of the relationship between changes in the intestinal environment and intestinal microbiota balance caused by dietary alterations.

Unintended consequences: Disrupting microbial communities of Nilaparvata lugens with non-target pesticides

Insects are frequently exposed to a range of insecticides that can alter the structure of the commensal microbiome. However, the effects of exposure to non-target pesticides (including non-target insecticides and fungicides) on insect pest microbiomes are still unclear. In the present study, we exposed Nilaparvata lugens to three target insecticides (nitenpyram, pymetrozine, and avermectin), a non-target insecticide (chlorantraniliprole), and two fungicides (propiconazole and tebuconazole), and observed changes in the microbiome's structure and function. Our results showed that both non-target insecticide and fungicides can disrupt the microbiome's structure. Specifically, symbiotic bacteria of N. lugens were more sensitive to non-target insecticide compared to target insecticide, while the symbiotic fungi were more sensitive to fungicides. We also found that the microbiome in the field strain was more stable under pesticides exposure than the laboratory strain (a susceptible strain), and core microbial species g_Pseudomonas, s_Acinetobacter soli, g_Lactobacillus, s_Metarhizium minus, and s_Penicillium citrinum were significantly affected by specifically pesticides. Furthermore, the functions of symbiotic bacteria in nutrient synthesis were predicted to be significantly reduced by non-target insecticide. Our findings contribute to a better understanding of the impact of non-target pesticides on insect microbial communities and highlight the need for scientific and rational use of pesticides.

Pesticide exposure and the microbiota-gut-brain axis

The gut microbiota exist within a dynamic ecosystem shaped by various factors that includes exposure to xenobiotics such as pesticides. It is widely regarded that the gut microbiota plays an essential role in maintaining host health, including a major influence on the brain and behaviour. Given the widespread use of pesticides in modern agriculture practices, it is important to assess the long-term collateral effects these xenobiotic exposures have on gut microbiota composition and function. Indeed, exposure studies using animal models have shown that pesticides can induce negative impacts on the host gut microbiota, physiology and health. In tandem, there is a growing body of literature showing that the effects of pesticide exposure can be extended to the manifestation of behavioural impairments in the host. With the increasing appreciation of the microbiota-gut-brain axis, in this review we assess whether pesticide-induced changes in gut microbiota composition profiles and functions could be driving these behavioural alterations. Currently, the diversity of pesticide type, exposure dose and variation in experimental designs hinders direct comparisons of studies presented. Although many insights presented, the mechanistic connection between the gut microbiota and behavioural changes remains insufficiently explored. Future experiments should therefore focus on causal mechanisms to examine the gut microbiota as the mediator of the behavioural impairments observed in the host following pesticide exposure.

The gut microbiome of solitary bees is mainly affected by pathogen assemblage and partially by land use

Pollinators, including solitary bees, are drastically declining worldwide. Among the factors contributing to this decline, bee pathogens and different land uses are of relevance. The link between the gut microbiome composition and host health has been recently studied for social pollinators (e.g. honeybees), whereas the information related to solitary bees is sparse. This work aimed at the characterization of the gut microbiome of the solitary bees Xylocopa augusti, Eucera fervens and Lasioglossum and attempted to correlate the gut microbial composition with the presence and load of different pathogens and land uses. Solitary bees were sampled in different sites (i.e. a farm, a natural reserve, and an urban plant nursery) showing different land uses. DNA was extracted from the gut, 16S rRNA gene amplified and sequenced. Eight pathogens, known for spillover from managed bees to wild ones, were quantified with qPCR. The results showed that the core microbiome profile of the three solitary bees significantly varied in the different species. Pseudomonas was found as the major core taxa in all solitary bees analyzed, whereas Lactobacillus, Spiroplasma and Sodalis were the second most abundant taxa in X. augusti, E. fervens and Lasioglossum, respectively. The main pathogens detected with qPCR were Nosema ceranae, Nosema bombi and Crithidia bombi, although differently abundant in the different bee species and sampling sites. Most microbial taxa did not show any correlation with the land use, apart from Snodgrassella and Nocardioides, showing higher abundances on less anthropized sites. Conversely, the pathogens species and load strongly affected the gut microbial composition, with Bifidobacterium, Apibacter, Serratia, Snodgrassella and Sodalis abundance that positively or negatively correlated with the detected pathogens load. Therefore, pathogens presence and load appear to be the main factor shaping the gut microbiome of solitary bees in Argentina.

Gut Microbiota Accelerate the Insecticidal Activity of Plastid-Expressed Bacillus thuringiensis Cry3Bb to a Leaf Beetle, Plagiodera versicolora

Bacillus thuringiensis is widely used as a biopesticide, and its crystal protein expressed in transgenic crops has been successfully used for the management of insect pests. However, whether the midgut microbiota contribute to the Bt insecticidal mechanism remains controversial. We previously demonstrated that transplastomic poplar plants expressing Bt Cry3Bb are highly lethal to willow leaf beetle (Plagiodera versicolora), one of the major pests causing severe damage to Salicaceae plants such as willows and poplars. Here, we demonstrate that feeding poplar leaves expressing Cry3Bb to nonaxenic P. versicolora larvae leads to significantly accelerated mortality, and overgrowth and dysbiosis of the gut microbiota, compared with axenic larvae. Corroborating work done with Lepidopteran insects, plastid-expressed Cry3Bb can cause the lysis of the beetle's intestinal cells, lead to the entry of intestinal bacteria into the body cavity, and thus cause the dynamic changes in the flora of the midgut and blood cavity in P. versicolora. Reintroduction of Pseudomonas putida, a gut bacterium of P. versicolora, into axenic P. versicolora larvae further enhances mortality upon feeding on Cry3Bb-expressing poplar. Our results indicate the important contribution of host gut microbiota in promoting the B. thuringiensis crystal protein insecticidal activity and provide new insights into the mechanism of pest control by Bt-transplastomic approaches. IMPORTANCE The contribution of gut microbiota to Bacillus thuringiensis Cry3Bb insecticidal activity in a leaf beetle was demonstrated using transplastomic poplar plants, providing a potential new approach to improve the efficiency of plastid transformation technology for pest control by expression of Bt toxins.

Axenic and gnotobiotic insect technologies in research on host-microbiota interactions

Insects are one of the most important animal life forms on earth. Symbiotic microbes are closely related to the growth and development of the host insects and can affect pathogen transmission. For decades, various axenic insect-rearing systems have been developed, allowing further manipulation of symbiotic microbiota composition. Here we review the historical development of axenic rearing systems and the latest progress in using axenic and gnotobiotic approaches to study insect-microbe interactions. We also discuss the challenges of these emerging technologies, possible solutions to address these challenges, and future research directions that can contribute to a more comprehensive understanding of insect-microbe interactions.

Multi-and transgenerational synergistic effects of glyphosate and chlorpyrifos at environmentally relevant concentrations in the estuarine rotifer Proales similis

We evaluated the multi-and transgenerational effects of single and combined environmentally relevant concentrations of glyphosate (GLY) and chlorpyrifos (CPF) in the estuarine rotifer Proales similis. The acute and chronic toxicities of GLY and CPF were determined as individual compounds and as a mixture. Rotifers were exposed to environmental concentrations of GLY (1, 10, 100, and 1000 μg/L) and CPF (0.1, 1, 5, and 10 μg/L). The main findings were as follows: (i) the LC₅₀ values were 33.91 mg/L (GLY) and 280 μg/L (CPF); (ii) the toxic unit (TU₅₀) of the mixture was 0.30, corresponding to 10.17 mg/L GLY and 83 μg/L CPF; (iii) the multigenerational study indicated that the tested concentrations of GLY and CPF, both single and combined, significantly and consistently decreased the growth rates of P. similis from the F0 to F6 generations; (iv) in most cases, GLY and CPF mixtures induced a strong synergistic effect; and (v) transgenerational effects were detected in the F4 generation, especially GLY and CPF in higher equitoxic proportions. These effects seem to dissipate in F5. Across multigeneration, a slight recovery could indicate population resilience to pollution. Our findings suggest that a mixture of GLY and CPF at environmental concentrations is likely to occur under real field conditions, increasing the risk to marine and estuarine invertebrates such as rotifers.

Nasonia-microbiome associations: a model for evolutionary hologenomics research

In recent years, with the development of microbial research technologies, microbiota research has received widespread attention. The parasitoid wasp genus Nasonia is a good model organism for studying insect behavior, development, evolutionary genetics, speciation, and symbiosis. This review describes key advances and progress in the field of the Nasonia-microbiome interactions. We provide an overview of the advantages of Nasonia as a model organism for microbiome studies, list research methods to study the Nasonia microbiome, and discuss recent discoveries in Nasonia microbiome research. This summary of the complexities of Nasonia-microbiome relationships will help to contribute to a better understanding of the interactions between animals and their microbiomes and establish a clear research direction for Nasonia-microbiome interactions in the future.

Ecosystem consequences of herbicides: the role of microbiome

Non-target organisms are globally exposed to herbicides. While many herbicides - for example, glyphosate - were initially considered safe, increasing evidence demonstrates that they have profound effects on ecosystem functions via altered microbial communities. We provide a comprehensive framework on how herbicide residues may modulate ecosystem-level outcomes via alteration of microbiomes. The changes in soil microbiome are likely to influence key nutrient cycling and plant-soil processes. Herbicide-altered microbiome affects plant and animal performance and can influence trophic interactions such as herbivory and pollination. These changes are expected to lead to ecosystem and even evolutionary consequences for both microbes and hosts. Tackling the threats caused by agrochemicals to ecosystem functions and services requires tools and solutions based on a comprehensive understanding of microbe-mediated risks.

Effects of Lifetime Exposures to Environmental Contaminants on the Adult Gut Microbiome

Emerging experimental evidence indicates that toxicant-induced alterations in gut microbiota composition and activity may affect host homeostasis. However, data from human studies are scarce; to our knowledge, no previous studies have quantified the association of lifetime exposure to environmental chemicals, across multiple time points, with the composition of the adult gut microbiome. Here we studied 124 individuals born in the Faroe Islands in 1986-1987 who were followed approximately every seven years from birth through age 28 years. Organochlorine compounds, including polychlorinated biphenyls (PCBs) and pesticides, perfluoroalkyl substances (PFAS), and mercury (Hg), were measured in cord blood and longitudinally in participants' blood. At age 28, the gut microbiome was assessed using shotgun metagenomic sequencing. Historical contaminant exposures had little direct effect on the adult gut microbiome, while a small number of fastidious anaerobes were weakly linked to recent PFAS/PFOS exposures at age 28. In this cohort, our findings suggest no lasting effects of early life exposures on adult gut microbial composition, but proximal exposures may contribute to gut microbiome alterations. The methods developed and used for this investigation may help in future identification of small but lasting impacts of environmental toxicant exposure on the gut microbiome.

Experimental inheritance of antibiotic acquired dysbiosis affects host phenotypes across generations

Microbiomes can enhance the health, fitness and even evolutionary potential of their hosts. Many organisms propagate favorable microbiomes fully or partially via vertical transmission. In the long term, such co-propagation can lead to the evolution of specialized microbiomes and functional interdependencies with the host. However, microbiomes are vulnerable to environmental stressors, particularly anthropogenic disturbance such as antibiotics, resulting in dysbiosis. In cases where microbiome transmission occurs, a disrupted microbiome may then become a contagious pathology causing harm to the host across generations. We tested this hypothesis using the specialized socially transmitted gut microbiome of honey bees as a model system. By experimentally passaging tetracycline-treated microbiomes across worker 'generations' we found that an environmentally acquired dysbiotic phenotype is heritable. As expected, the antibiotic treatment disrupted the microbiome, eliminating several common and functionally important taxa and strains. When transmitted, the dysbiotic microbiome harmed the host in subsequent generations. Particularly, naïve bees receiving antibiotic-altered microbiomes died at higher rates when challenged with further antibiotic stress. Bees with inherited dysbiotic microbiomes showed alterations in gene expression linked to metabolism and immunity, among other pathways, suggesting effects on host physiology. These results indicate that there is a possibility that sublethal exposure to chemical stressors, such as antibiotics, may cause long-lasting changes to functional host-microbiome relationships, possibly weakening the host's progeny in the face of future ecological challenges. Future studies under natural conditions would be important to examine the extent to which negative microbiome-mediated phenotypes could indeed be heritable and what role this may play in the ongoing loss of biodiversity.

Managing the efficiencies of three different bacterial isolates for removing atrazine from wastewater

Three individual bacterial isolates previously isolated from two types of soil with a different history of atrazine applications were chosen, purified, and subjected to subsequent work. Identification of the individual bacterial isolates was conducted using molecular methods 16S rRNA and then tested for their atrazine degradation potentials. Effects of different parameters like mixing, starvation, UV exposure, and sodium citrate for enhancing the atrazine bioremediation process by identified bacteria were also studied. The molecular method identified individual bacterial isolates as Stenotrophomonas sp. strain SD2 (strain SD2), Bacillus cereus strain BC3 (strain BC3), and Paenarthrobacter ureafaciens strain AD3 (strain AD3). The bacterial isolate strain AD3 was able to degrade 47.95% of atrazine after 28 days. Mixing strain AD3 with strain BC3 showed almost doubled of atrazine degradation percentage (61.39%) of using strain BC3 as an individual isolate (36.59%). The atrazine degradation efficacy for Stenotrophomonas sp. strain SD2, Bacillus cereus strain BC3, and Paenarthrobacter ureafaciens strain AD3 was increased between 1.28 and 4.32 folds after the starvation process. The UV exposure enhanced the efficiencies of the tested isolates either individual or mixtures (from 1.08 to 4.63-fold). Adding sodium citrate as a stimulator to the media of growing the tested isolates enhanced their potential for atrazine degradation.

Pesticide soil microbial toxicity: setting the scene for a new pesticide risk assessment for soil microorganisms (IUPAC Technical Report)

Pesticides constitute an integral part of modern agriculture. However, there are still concerns about their effects on non-target organisms. To address this the European Commission has imposed a stringent regulatory scheme for new pesticide compounds. Assessment of the aquatic toxicity of pesticides is based on a range of advanced tests. This does not apply to terrestrial ecosystems, where the toxicity of pesticides on soil microorganisms, is based on an outdated and crude test (N mineralization). This regulatory gap is reinforced by the recent methodological and standardization advances in soil microbial ecology. The inclusion of such standardized tools in a revised risk assessment scheme will enable the accurate estimation of the toxicity of pesticides on soil microorganisms and on associated ecosystem services. In this review we (i) summarize recent work in the assessment of the soil microbial toxicity of pesticides and point to ammonia-oxidizing microorganisms (AOM) and arbuscular mycorrhizal fungi (AMF) as most relevant bioindicator groups (ii) identify limitations in the experimental approaches used and propose mitigation solutions, (iii) identify scientific gaps and (iv) propose a new risk assessment procedure to assess the effects of pesticides on soil microorganisms.

Contribution of insect gut microbiota and their associated enzymes in insect physiology and biodegradation of pesticides

Synthetic pesticides are extensively and injudiciously applied to control agriculture and household pests worldwide. Due to their high use, their toxic residues have enormously increased in the agroecosystem in the past several years. They have caused many severe threats to non-target organisms, including humans. Therefore, the complete removal of toxic compounds is gaining wide attention to protect the ecosystem and the diversity of living organisms. Several methods, such as physical, chemical and biological, are applied to degrade compounds, but as compared to other methods, biological methods are considered more efficient, fast, eco-friendly and less expensive. In particular, employing microbial species and their purified enzymes makes the degradation of toxic pollutants more accessible and converts them into non-toxic products by several metabolic pathways. The digestive tract of insects is usually known as a superior organ that provides a nutrient-rich environment to hundreds of microbial species that perform a pivotal role in various physiological and ecological functions. There is a direct relationship between pesticides and insect pests: pesticides reduce the growth of insect species and alter the phyla located in the gut microbiome. In comparison, the insect gut microbiota tries to degrade toxic compounds by changing their toxicity, increasing the production and regulation of a diverse range of enzymes. These enzymes breakdown into their derivatives, and microbial species utilize them as a sole source of carbon, sulfur and energy. The resistance of pesticides (carbamates, pyrethroids, organophosphates, organochlorines, and neonicotinoids) in insect species is developed by metabolic mechanisms, regulation of enzymes and the expression of various microbial detoxifying genes in insect guts. This review summarizes the toxic effects of agrochemicals on humans, animals, birds and beneficial arthropods. It explores the preferential role of insect gut microbial species in the degradation process and the resistance mechanism of several pesticides in insect species. Additionally, various metabolic pathways have been systematically discussed to better understand the degradation of xenobiotics by insect gut microbial species.

Reciprocal interactions between anthropogenic stressors and insect microbiota

Insects play many important roles in nature due to their diversity, ecological role, and impact on agriculture or human health. They are directly influenced by environmental changes and in particular anthropic activities that constitute an important driver of change in the environmental characteristics. Insects face numerous anthropogenic stressors and have evolved various detoxication mechanisms to survive and/or resist to these compounds. Recent studies highligted the pressure exerted by xenobiotics on insect life-cycle and the important role of insect-associated bacterial microbiota in the insect responses to environmental changes. Stressor exposure can have various impacts on the composition and structure of insect microbiota that in turn may influence insect biology. Moreover, bacterial communities associated with insects can be directly or indirectly involved in detoxification processes with the selection of certain microorganisms capable of degrading xenobiotics. Further studies are needed to assess the role of insect-associated microbiota as key contributor to the xenobiotic metabolism and thus as a driver for insect adaptation to polluted habitats.

Evolution of pesticide tolerance and associated changes in the microbiome in the water flea Daphnia magna

Exposure to pesticides can have detrimental effects on aquatic communities of non-target species. Populations can evolve tolerance to pesticides which may rescue them from extinction. However, the evolution of tolerance does not always occur and insights in the underlying mechanisms are scarce. One understudied mechanism to obtain pesticide tolerance in hosts are shifts toward pesticide-degrading bacteria in their microbiome. We carried out experimental evolution trials where replicated experimental populations of the water flea Daphnia magna were exposed to the pesticide chlorpyrifos or a solvent control, after which we performed acute toxicity assays to evaluate the evolution of chlorpyrifos tolerance. Additionally, we quantified changes in the microbiota community composition of whole body and gut samples to assess which sample type best reflected the pesticide tolerance of the Daphnia host. As expected, chlorpyrifos-selected clones became more tolerant to chlorpyrifos as shown by the higher EC_5048 h (36% higher) compared with the control clones. This was associated with shifts in the microbiome composition whereby the abundance of known organophosphate-degrading bacterial genera increased on average ~4 times in the chlorpyrifos-selected clones. Moreover, the abundances of several genera, including the organophosphate-degrading bacteria Pseudomonas, Flavobacterium and Bacillus, were positively correlated with the EC_5048 h of the host populations. These shifts in bacterial genera were similar in magnitude in whole body and gut samples, yet the total abundance of organophosphate-degrading bacteria was ~6 times higher in the whole body samples, suggesting that the gut is not the only body part where pesticide degradation by the microbiome occurs. Our results indicate that the microbiome is an important mediator of the development of tolerance to pesticides in Daphnia.

The Mechanism of Chlorantraniliprole Resistance and Detoxification in Trichogramma chilonis (Hymenoptera: Trichogrammatidae)

Parasitic Trichogramma chilonis Ishii, an egg parasitoid of Grapholita molesta, is a critical agent for biological control of insect pests in crop plants. However, the efficiency of T. chilonis is influenced by its resistance to the common pesticide chlorantraniliprole. To elucidate the chlorantraniliprole detoxification mechanism, differentially expressed genes (DEGs) related to chlorantraniliprole resistance were studied at different developmental stages of the wasp. Individuals of T. chilonis were grouped and treated with chlorantraniliprole at different developmental stages. Untreated wasps were used as controls. Transcriptomic analysis identified the DEGs associated with chlorantraniliprole resistance and detoxification in T. chilonis. A total of 1,483 DEGs were associated with chlorantraniliprole resistance at all developmental stages. DEGs that correlated with chlorantraniliprole sensitivity of T. chilonis at different developmental stages were distinct and had various functions. The newly identified DEGs are involved in cytochrome P450- and glutathione metabolism-related pathways, which were predicted to contribute to chlorantraniliprole detoxification. Chlorantraniliprole detoxification by T. chilonis was associated with cytochrome P450- and glutathione-related pathways. Our findings may be useful for balancing chemical and biological control practices aimed to optimize agricultural production.

The Role of Insect Symbiotic Bacteria in Metabolizing Phytochemicals and Agrochemicals

Simple Summary

To counter plant chemical defenses and exposure to agrochemicals, herbivorous insects have developed several adaptive strategies to guard against the ingested detrimental substances, including enhancing detoxifying enzyme activities, avoidance behavior, amino acid mutation of target sites, and lower penetration through a thicker cuticle. Insect microbiota play important roles in many aspects of insect biology and physiology. To better understand the role of insect symbiotic bacteria in metabolizing these detrimental substances, we summarize the research progress on the function of insect bacteria in metabolizing phytochemicals and agrochemicals, and describe their future potential application in pest management and protection of beneficial insects.

Abstract

The diversity and high adaptability of insects are heavily associated with their symbiotic microbes, which include bacteria, fungi, viruses, protozoa, and archaea. These microbes play important roles in many aspects of the biology and physiology of insects, such as helping the host insects with food digestion, nutrition absorption, strengthening immunity and confronting plant defenses. To maintain normal development and population reproduction, herbivorous insects have developed strategies to detoxify the substances to which they may be exposed in the living habitat, such as the detoxifying enzymes carboxylesterase, glutathione-S-transferases (GSTs), and cytochrome P450 monooxygenases (CYP450s). Additionally, insect symbiotic bacteria can act as an important factor to modulate the adaptability of insects to the exposed detrimental substances. This review summarizes the current research progress on the role of insect symbiotic bacteria in metabolizing phytochemicals and agrochemicals (insecticides and herbicides). Given the importance of insect microbiota, more functional symbiotic bacteria that modulate the adaptability of insects to the detrimental substances to which they are exposed should be identified, and the underlying mechanisms should also be further studied, facilitating the development of microbial-resource-based pest control approaches or protective methods for beneficial insects.

A Margulian View of Symbiosis and Speciation: the Nasonia Wasp System

Species are fundamental units of biology that exemplify lineage diversification, while symbiosis of microbes and macrobial hosts exemplify lineage unification between the domains of life. While these conceptual differences between speciation and symbiosis often dominate the narrative of the respective fields, Lynn Margulis argued for interconnection between these two subdisciplines of biology in a manner that left a legacy for scholars and students alike to pursue, detail, and discover. The Margulian perspective has always been that host evolutionary processes such as speciation are more impacted by microbial symbioses than typically appreciated. In this article, we present and review the case system that she long envisioned, one in which layers of microbial symbiosis reduce species interbreeding and assist species diversification among a closely related group of small, metallic green, parasitoid wasps from the genus Nasonia.

Bacillus velezensis EEAM 10B Strengthens Nutrient Metabolic Process in Black Soldier Fly Larvae (Hermetia illucens) via Changing Gut Microbiome and Metabolic Pathways

Insects are a potential alternative protein source to solve the food shortage crisis. Previous studies have illustrated that probiotics can improve the substrate conversion efficiency of insects and increase insect protein content. However, the effects of probiotics on insect physiology and nutrient metabolism are still not well understood. Here, the black soldier fly larvae (BSFL), Hermetia illucens (Diptera: Stratiomyidae), was used as a study subject to deeply investigate the specific interaction among a novel probiotic, Bacillus velezensis EEAM 10B (10B), intestinal microbiota, and the host. In this study, the effects of 10B on the survival and physiology of BSFL were first analyzed. It shows that 10B significantly elevated the substrate conversion rate, average dry weight, and protein content of BSFL by 5%, 0.13 g/pc, and 8%, respectively. Then, we assessed the effect of 10B on the microbial community composition in the gut and frass of BSFL using Illumina Miseq sequencing. It shows that 10B significantly altered the microbial composition of the gut, but not that of the frass. Pearson’s correlation analysis further showed that the Bacillus, unclassified_of_Caloramatoraceae, and Gracilibacillus were positively correlated with the survival rate, crude protein content, and substrate conversion rate of BSFL. To further investigate the effect of 10B on host metabolism, metabolic analyses on germ-free BSFL, monobacterial intestinal BSFL, and natural BSFL were also performed. The results proved that 10B (i) played a vital role in the survival of BSFL; and (ii) regulated the amino acid synthetic and metabolic process of BSFL, thus leading to the rise of the protein content of BSFL. In addition, vitamin backfill assays verified that the BSFL survival rate was significantly improved by supplying the germ-free BSFL with riboflavin, which further suggests that 10B determines the survival of BSFL via delivering riboflavin. Overall, this study provides a reference for understanding the comprehensive contribution of a specific probiotic to its host.

Role of Insect Gut Microbiota in Pesticide Degradation: A Review

Insect pests cause significant agricultural and economic losses to crops worldwide due to their destructive activities. Pesticides are designed to be poisonous and are intentionally released into the environment to combat the menace caused by these noxious pests. To survive, these insects can resist toxic substances introduced by humans in the form of pesticides. According to recent findings, microbes that live in insect as symbionts have recently been found to protect their hosts against toxins. Symbioses that have been formed are between the pests and various microbes, a defensive mechanism against pathogens and pesticides. Insects' guts provide unique conditions for microbial colonization, and resident bacteria can deliver numerous benefits to their hosts. Insects vary significantly in their reliance on gut microbes for basic functions. Insect digestive tracts are very different in shape and chemical properties, which have a big impact on the structure and composition of the microbial community. Insect gut microbiota has been found to contribute to feeding, parasite and pathogen protection, immune response modulation, and pesticide breakdown. The current review will examine the roles of gut microbiota in pesticide detoxification and the mechanisms behind the development of resistance in insects to various pesticides. To better understand the detoxifying microbiota in agriculturally significant pest insects, we provided comprehensive information regarding the role of gut microbiota in the detoxification of pesticides.

Disentangling host-microbiota complexity through hologenomics

Research on animal-microbiota interactions has become a central topic in biological sciences because of its relevance to basic eco-evolutionary processes and applied questions in agriculture and health. However, animal hosts and their associated microbial communities are still seldom studied in a systemic fashion. Hologenomics, the integrated study of the genetic features of a eukaryotic host alongside that of its associated microbes, is becoming a feasible - yet still underexploited - approach that overcomes this limitation. Acknowledging the biological and genetic properties of both hosts and microbes, along with the advantages and disadvantages of implemented techniques, is essential for designing optimal studies that enable some of the major questions in biology to be addressed.

Earwig mothers consume the feces of their juveniles during family life

Many animals consume the feces of their conspecifics. This allo-coprophagy can have benefits, such as access to nutrients and symbionts, but also risks for consumers, mainly due to direct contact with pathogens that develop on feces. In the European earwig Forficula auricularia, mothers and juveniles live in nests lined with their feces. This surprising habit allows juveniles to consume the feces of their siblings during family life and provides them with nutritional benefits when mothers provide low care. However, it was unclear whether earwig mothers also practice allo-coprophagy, and whether this behavior is motivated by their nutritional needs. Here, we set up four types of experimental families in which we manipulated the nutritional needs of mothers and/or juveniles and measured the effects on the production of feces by the juveniles, and the consumption of these feces by the mothers. Our results first show that fed juveniles produced more feces pellet in presence of fed compared to food-deprived mothers. We also found that, overall, about 50% of the mothers consumed juveniles feces. This consumption was both more likely and larger when the feces were produced by fed compared to food-deprived juveniles, while the proportion of feces pellets eaten was larger in food-deprived compared to fed mothers. Overall, our results reveal that allo-coprophagy involves every family member and suggest that it can have both nutritional and non-nutritional benefits for earwig mothers. Allo-coprophagy could thus favor the maintenance of mothers in the nest and, more generally, promote the early evolution of family life.

Gut Microbiota: A Key Regulator in the Effects of Environmental Hazards on Modulates Insulin Resistance

Insulin resistance is a hallmark of Alzheimer’s disease (AD), type II diabetes (T2D), and Parkinson’s disease (PD). Emerging evidence indicates that these disorders are typically characterized by alterations in the gut microbiota composition, diversity, and their metabolites. Currently, it is understood that environmental hazards including ionizing radiation, toxic heavy metals, pesticides, particle matter, and polycyclic aromatic hydrocarbons are capable of interacting with gut microbiota and have a non-beneficial health effect. Based on the current study, we propose the hypothesis of “gut microenvironment baseline drift”. According to this “baseline drift” theory, gut microbiota is a temporarily combined cluster of species sharing the same environmental stresses for a short period, which would change quickly under the influence of different environmental factors. This indicates that the microbial species in the gut do not have a long-term relationship; any split, division, or recombination may occur in different environments. Nonetheless, the “baseline drift” theory considers the critical role of the response of the whole gut microbiome. Undoubtedly, this hypothesis implies that the gut microbiota response is not merely a “cross junction” switch; in contrast, the human health or disease is a result of a rich palette of gut-microbiota-driven multiple-pathway responses. In summary, environmental factors, including hazardous and normal factors, are critical to the biological impact of the gut microbiota responses and the dual effect of the gut microbiota on the regulation of biological functions. Novel appreciation of the role of gut microbiota and environmental hazards in the insulin resistance would shed new light on insulin resistance and also promote the development of new research direction and new overcoming strategies for patients.

An optimized method for Nasonia germ-free rearing

A germ-free rearing system is a crucial method for host–microbiota interactions using Nasonia as a model system. The previous rearing media in 2012 introduced toxic factors like bleach and antibiotics, required significant effort and volume of media preparation, and the rearing protocols in 2012 and 2016 often resulted in embryos, larvae, and enclosing pupae drowning, underfed, or desiccating. In this work, we optimize the germ-free rearing media that excludes the toxic factors and provide a substrate for the developing animals to have constant access to media without the risk of drowning or desiccation. The new process resulted in an increase in full maturation of larvae to adults from 33 to 65%, with no effect on the rate of growth or final adult size. This significantly improves the applicability of germ-free rearing of Nasonia and potentially other parasitoids.

Isolation, Identification, and Analysis of Potential Functions of Culturable Bacteria Associated with an Invasive Gall Wasp, Leptocybe invasa

Symbioses between invasive insects and bacteria are one of the key drivers of insect invasion success. Gall-inducing insects stimulate host plants to produce galls, which affects the normal growth of plants. Leptocybe invasa Fisher et La Salle, an invasive gall-inducing wasp, mainly damages Eucalyptus plantations in Southern China, but little is known about its associated bacteria. The aim of this study was to assess the diversity of bacterial communities at different developmental stages of L. invasa and to identify possible ecological functions of the associated bacteria. Bacteria associated with L. invasa were isolated using culture-dependent methods and their taxonomic statuses were determined by sequencing the 16S rRNA gene. A total of 88 species belonging to four phyla, 27 families, and 44 genera were identified by phylogenetic analysis. The four phyla were Proteobacteria, Actinobacteria, Firmicutes, and Bacteroidetes, mainly from the genera Pantoea, Enterobacter, Pseudomonas, Bacillus, Acinetobacter, Curtobacterium, Sphingobium, Klebsiella, and Rhizobium. Among them, 72 species were isolated in the insect gall stage and 46 species were isolated from the adult stage. The most abundant bacterial species were γ-Proteobacteria. We found significant differences in total bacterial counts and community compositions at different developmental stages, and identified possible ecological roles of L. invasa-associated bacteria. This study is the first to systematically investigate the associated bacteria of L. invasa using culture-dependent methods, and provides a reference for other gall-inducing insects and associated bacteria.

Herbicide Selection Promotes Antibiotic Resistance in Soil Microbiomes

Herbicides are one of the most widely used chemicals in agriculture. While they are known to be harmful to nontarget organisms, the effects of herbicides on the composition and functioning of soil microbial communities remain unclear. Here we show that application of three widely used herbicides—glyphosate, glufosinate, and dicamba—increase the prevalence of antibiotic resistance genes (ARGs) and mobile genetic elements (MGEs) in soil microbiomes without clear changes in the abundance, diversity and composition of bacterial communities. Mechanistically, these results could be explained by a positive selection for more tolerant genotypes that acquired several mutations in previously well-characterized herbicide and ARGs. Moreover, herbicide exposure increased cell membrane permeability and conjugation frequency of multidrug resistance plasmids, promoting ARG movement between bacteria. A similar pattern was found in agricultural soils across 11 provinces in China, where herbicide application, and the levels of glyphosate residues in soils, were associated with increased ARG and MGE abundances relative to herbicide-free control sites. Together, our results show that herbicide application can enrich ARGs and MGEs by changing the genetic composition of soil microbiomes, potentially contributing to the global antimicrobial resistance problem in agricultural environments.

Diversity and Functions of Yeast Communities Associated with Insects

Following the concept of the holobiont, insect-microbiota interactions play an important role in insect biology. Many examples of host-associated microorganisms have been reported to drastically influence insect biological processes such as development, physiology, nutrition, survival, immunity, or even vector competence. While a huge number of studies on insect-associated microbiota have focused on bacteria, other microbial partners including fungi have been comparatively neglected. Yeasts, which establish mostly commensal or symbiotic relationships with their host, can dominate the mycobiota of certain insects. This review presents key advances and progress in the research field highlighting the diversity of yeast communities associated with insects, as well as their impact on insect life-history traits, immunity, and behavior.

Phylogenetically closely related pseudomonads isolated from arthropods exhibit differential insect-killing abilities and genetic variations in insecticidal factors

Strains belonging to the Pseudomonas protegens and Pseudomonas chlororaphis species are able to control soilborne plant pathogens and to kill pest insects by producing virulence factors such as toxins, chitinases, antimicrobials or two‐partner secretion systems. Most insecticidal Pseudomonas described so far were isolated from roots or soil. It is unknown whether these bacteria naturally occur in arthropods and how they interact with them. Therefore, we isolated P. protegens and P. chlororaphis from various healthy insects and myriapods, roots and soil collected in an agricultural field and a neighbouring grassland. The isolates were compared for insect killing, pathogen suppression and host colonization abilities. Our results indicate that neither the origin of isolation nor the phylogenetic position mirror the degree of insecticidal activity. Pseudomonas protegens strains appeared homogeneous regarding phylogeny, biocontrol and insecticidal capabilities, whereas P. chlororaphis strains were phylogenetically and phenotypically more heterogenous. A phenotypic and genomic analysis of five closely related P. chlororaphis isolates displaying varying levels of insecticidal activity revealed variations in genes encoding insecticidal factors that may account for the reduced insecticidal activity of certain isolates. Our findings point towards an adaption to insects within closely related pseudomonads and contribute to understand the ecology of insecticidal Pseudomonas.

Toxicology and Microbiota: How Do Pesticides Influence Gut Microbiota? A Review

In recent years, new targets have been included between the health outcomes induced by pesticide exposure. The gastrointestinal tract is a key physical and biological barrier and it represents a primary site of exposure to toxic agents. Recently, the intestinal microbiota has emerged as a notable factor regulating pesticides’ toxicity. However, the specific mechanisms related to this interaction are not well known. In this review, we discuss the influence of pesticide exposure on the gut microbiota, discussing the factors influencing gut microbial diversity, and we summarize the updated literature. In conclusion, more studies are needed to clarify the host–microbial relationship concerning pesticide exposure and to define new prevention interventions, such as the identification of biomarkers of mucosal barrier function.

The microbiome and mosquito vectorial capacity: rich potential for discovery and translation

Microbiome research has gained considerable interest due to the emerging evidence of its impact on human and animal health. As in other animals, the gut-associated microbiota of mosquitoes affect host fitness and other phenotypes. It is now well established that microbes can alter pathogen transmission in mosquitoes, either positively or negatively, and avenues are being explored to exploit microbes for vector control. However, less attention has been paid to how microbiota affect phenotypes that impact vectorial capacity. Several mosquito and pathogen components, such as vector density, biting rate, survival, vector competence, and the pathogen extrinsic incubation period all influence pathogen transmission. Recent studies also indicate that mosquito gut-associated microbes can impact each of these components, and therefore ultimately modulate vectorial capacity. Promisingly, this expands the options available to exploit microbes for vector control by also targeting parameters that affect vectorial capacity. However, there are still many knowledge gaps regarding  mosquito-microbe interactions  that need to be addressed in order to exploit them efficiently. Here, we review current evidence of impacts of the microbiome on aspects of vectorial capacity, and we highlight likely opportunities for novel vector control strategies and areas where further studies are required. Video abstract.

Atrazine detoxification by intracellular crude enzyme extracts derived from epiphytic root bacteria associated with emergent hydrophytes

The present study demonstrated atrazine detoxification by intracellular crude enzyme extracts of Pseudomonas spp. strains ACB and TLB. Indigenous bacterial protein-based remediation techniques could be an alternative to bioaugmentation which pose multiple challenges when applied to the field. Intracellular enzymes were extracted from strains ACB and TLB and their degradation potential of 10 mg L^-1 was determined using Gas Chromatography; further, enzyme extracts were subjected to protein profiling studies. In span of 6 h, enzyme extracts of strain ACB showed maximum degradation at 30 °C and 40 °C (71%) and enzyme extracts of strain TLB showed maximum degradation at 40 °C (48%). Atrazine degradation by enzyme extracts of strain ACB showed maximum degradation at pH 7 (71%) and pH 6 (69%) in 6 h. Similarly, enzyme extracts of strain TLB showed maximal degradation at pH 6 (46%) in 6 h. The present study demonstrated, for the first time, efficient atrazine remediation by intracellular crude enzyme extracts from epiphytic root bacteria at a range of temperature and pH conditions. Protein profiling studies indicated that atrazine induced expression of CoA ester lyase and alkyl hydroperoxide reductase in the strains ACB and TLB respectively. Expressions of these proteins have never been associated with atrazine exposure.

Alteration of gut microbiota with a broad-spectrum antibiotic does not impair maternal care in the European earwig

The microbes residing within the gut of an animal host often increase their own fitness by modifying their host's physiological, reproductive and behavioural functions. Whereas recent studies suggest that they may also shape host sociality and therefore have critical effects on animal social evolution, the impact of the gut microbiota on maternal care remains unexplored. This is surprising, as this behaviour is widespread among animals, often determines the fitness of both juveniles and parents, and is essential in the evolution of complex animal societies. Here, we tested whether life-long alterations of the gut microbiota with rifampicin-a broad-spectrum antibiotic-impair pre- and post-hatching maternal care in the European earwig. Our results first confirm that rifampicin altered the mothers' gut microbial communities and indicate that the composition of the gut microbiota differs before and after egg care. Contrary to our predictions, however, the rifampicin-induced alterations of the gut microbiota did not modify pre- or post-hatching care. Independent of maternal care, rifampicin increased the females' faeces production and resulted in lighter eggs and juveniles. By contrast, rifampicin altered none of the other 21 physiological, reproductive and longevity traits measured over the 300 days of a female's lifetime. Overall, these findings reveal that altering the gut microbiota with a large spectrum antibiotic such as rifampicin does not necessarily affect host sociality. They also emphasize that not all animals have evolved a co-dependence with their microbiota and call for caution when generalizing the central role of gut microbes in host biology.

Coadaptation between host genome and microbiome under long-term xenobiotic-induced selection

One of the most difficult experimental challenges today is testing the evolutionary dynamics shaping complex host-microbiome interactions. We investigated host-microbiome codiversification in response to xenobiotic-induced selection using an experimental evolution approach. To this end, we exposed the parasitoid wasp Nasonia vitripennis to sublethal concentrations of the widely used herbicide atrazine for 85 generations. Our results reveal that atrazine exposure not only mediated adaptive changes within the microbiome, which conferred host resistance to atrazine toxicity, but also exerted selective pressure on the host genome and altered host gene expression and immune response. Furthermore, microbiome transplant experiments reveal a decreased survival of adults from the control population after exposure to the evolved microbiome of the atrazine-exposed population, while no such decrease occurred in the reciprocal transplant. These results indicate that xenobiotic-induced selection mediated host-microbiome coadaptation, ultimately leading to a new host genome-microbiome equilibrium.

When your host shuts down: larval diapause impacts host-microbiome interactions in Nasonia vitripennis

BACKGROUND

The life cycles of many insect species include an obligatory or facultative diapause stage with arrested development and low metabolic activity as an overwintering strategy. Diapause is characterised by profound physiological changes in endocrine activity, cell proliferation and nutrient metabolism. However, little is known regarding host-microbiome interactions during diapause, despite the importance of bacterial symbionts for host nutrition and development. In this work, we investigated (i) the role of the microbiome for host nutrient allocation during diapause and (ii) the impact of larval diapause on microbiome dynamics in the parasitoid wasp Nasonia vitripennis, a model organism for host-microbiome interactions.

RESULTS

Our results demonstrate that the microbiome is essential for host nutrient allocation during diapause in N. vitripennis, as axenic diapausing larvae had consistently lower glucose and glycerol levels than conventional diapausing larvae, especially when exposed to cold temperature. In turn, microbiome composition was altered in diapausing larvae, potentially due to changes in the surrounding temperature, host nutrient levels and a downregulation of host immune genes. Importantly, prolonged larval diapause had a transstadial effect on the adult microbiome, with unknown consequences for host fitness. Notably, the most dominant microbiome member, Providencia sp., was drastically reduced in adults after more than 4 months of larval diapause, while potential bacterial pathogens increased in abundance.

CONCLUSION

This work investigates host-microbiome interactions during a crucial developmental stage, which challenges both the insect host and its microbial associates. The impact of diapause on the microbiome is likely due to several factors, including altered host regulatory mechanisms and changes in the host environment. Video Abstract.