Microbiome facilitated pest resistance: potential problems and uses

(±)-Catechins inhibit prehaustorium formation in the parasitic weed Phelipanche ramosa and reduce tomato infestation

BACKGROUND

Phelipanche ramosa L. (Pomel) is a noxious parasitic weed in field and vegetable crops in Mediterranean countries. Control of this pest is complex and far from being achieved, and new environmentally-friendly strategies are being sought. The present study evaluates the possibility of using (±)-catechins as a natural herbicide against broomrapes.

RESULTS

The results show that (±)-catechins have no effect on GR24-induced germination over a wide concentration range (10-4 to 10-10 m), nor on radicle elongation after germination, but strongly inhibit, at 10-4 and 10-5 m, prehaustorium formation in response to the haustorium-inducing factor, cis/trans-zeatin. Accordingly, pot experiments involving the supplies of 10-5 m of (±)-catechins to tomato plants infested or not with P. ramosa demonstrate that (±)-catechins do not influence growth of non-parasitized tomato plants and prevent heavy infestation by strongly reducing parasite attachments and inducing parasite necrosis once they are attached.

CONCLUSION

This study points the potential use of (±)-catechins for parasitic weed control. It raises also the question of the mechanisms involved in the inhibition of prehaustorium formation and the necrosis of parasite attachments in response to (±)-catechins application. © 2024 The Author(s). Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Mosquito Gut Microbiota: A Review

Mosquitoes are vectors of many important human diseases. The prolonged and widespread use of insecticides has led to the development of mosquito resistance to these insecticides. The gut microbiota is considered the master of host development and physiology; it influences mosquito biology, disease pathogen transmission, and resistance to insecticides. Understanding the role and mechanisms of mosquito gut microbiota in mosquito insecticide resistance is useful for developing new strategies for tackling mosquito insecticide resistance. We searched online databases, including PubMed, MEDLINE, SciELO, Web of Science, and the Chinese Science Citation Database. We searched all terms, including microbiota and mosquitoes, or any specific genera or species of mosquitoes. We reviewed the relationships between microbiota and mosquito growth, development, survival, reproduction, and disease pathogen transmission, as well as the interactions between microbiota and mosquito insecticide resistance. Overall, 429 studies were included in this review after filtering 8139 search results. Mosquito gut microbiota show a complex community structure with rich species diversity, dynamic changes in the species composition over time (season) and across space (environmental setting), and variation among mosquito species and mosquito developmental stages (larval vs. adult). The community composition of the microbiota plays profound roles in mosquito development, survival, and reproduction. There was a reciprocal interaction between the mosquito midgut microbiota and virus infection in mosquitoes. Wolbachia, Asaia, and Serratia are the three most studied bacteria that influence disease pathogen transmission. The insecticide resistance or exposure led to the enrichment or reduction in certain microorganisms in the resistant mosquitoes while enhancing the abundance of other microorganisms in insect-susceptible mosquitoes, and they involved many different species/genera/families of microorganisms. Conversely, microbiota can promote insecticide resistance in their hosts by isolating and degrading insecticidal compounds or altering the expression of host genes and metabolic detoxification enzymes. Currently, knowledge is scarce about the community structure of mosquito gut microbiota and its functionality in relation to mosquito pathogen transmission and insecticide resistance. The new multi-omics techniques should be adopted to find the links among environment, mosquito, and host and bring mosquito microbiota studies to the next level.

Novel Insecticidal Butenolide-Containing Methylxanthine Derivatives: Synthesis, Crystal Structure, Biological Activity Evaluation, DFT Calculation and Molecular Docking

The design of novel agrochemicals starting from bioactive natural products is one of the most effective ways in the discovery and development of new pesticidal agents. In this paper, a series of novel butenolide-containing methylxanthine derivatives (Ia-Ir) were designed based on natural methylxanthine caffeine and stemofoline, and the derivatized insecticide flupyradifurone of the latter. The structures of the synthesized compounds were confirmed via 1H-NMR, 13C NMR, HRMS and X-ray single crystal diffraction analyses. The biological activities of the compounds were evaluated against a variety of agricultural pests including oriental armyworm, bean aphid, diamondback moth, fall armyworm, cotton bollworm, and corn borer; the results indicated that some of them have favorable insecticidal potentials, particularly toward diamondback moth. Among others, Ic and Iq against diamondback moth possessed LC50 values of 6.187 mg ⋅ L-1 and 3.269 mg ⋅ L-1, respectively, - 2.5- and 4.8-fold of relative insecticidal activity respectively to that of flupyradifurone (LC50=15.743 mg ⋅ L-1). Additionally, both the DFT theoretical calculation and molecular docking with acetylcholine binding protein were conducted for the highly bioactive compound (Ic). Ic and Iq derived from the integration of caffeine (natural methylxanthine) and butenolide motifs can serve as novel leading insecticidal compounds for further optimization.

Discussion: Harnessing microbiome-mediated adaptations in insect pollinators to mitigate climate change impact on crop pollination

Insect pollinators, vital for agriculture and biodiversity, face escalating threats from climate change. We argue and explore the pivotal role of the microbiomes in shaping adaptations of insect pollinator resilience amid climate-induced challenges (climate change and habitat alteration). Examining diverse taxonomic groups, we unravel the interplay between insect physiology, microbiomes, and adaptive mechanisms. Climate-driven alterations in microbiomes impact insect health, behavior, and plant interactions, posing significant effects on agricultural ecosystems. We propose harnessing microbiome-mediated adaptations as a strategic approach to mitigate climate change impacts on crop pollination. Insights into insect-pollinator microbiomes offer transformative avenues for sustainable agriculture, including probiotic interventions (use of EM PROBIOTIC) and microbiome engineering (such as engineering gut bacteria) to induce immune responses and enhanced pollination services. Integrating microbiome insights into conservation practices elucidates strategies for preserving pollinator habitats, optimizing agricultural landscapes, and developing policies to safeguard pollinator health in the face of environmental changes. Finally, we stress interdisciplinary collaboration and the urgency of understanding pollinator microbiome dynamics under climate change in future research.

Tetracycline inhibits tick host reproduction by modulating bacterial microbiota, gene expression and metabolism levels

BACKGROUND

Ticks are disease vectors that are a matter of worldwide concern. Antibiotic treatments have been used to explore the interactions between ticks and their symbiotic microorganisms. In addition to altering the host microbial community, antibiotics can have toxic effects on the host.

RESULTS

In the tick Haemaphysalis longicornis, engorged females showed reproductive disruption after microinjection of tetracycline. Multi-omics approaches were implemented to unravel the mechanisms of tick reproductive inhibition in this study. There were no significant changes in bacterial density in the whole ticks on Day (D)2 or D4 after tetracycline treatment, whereas the bacterial microbial community was significantly altered, especially on D4. The relative abundances of the bacteria Staphylococcus, Bacillus and Pseudomonas decreased after tetracycline treatment, whereas the relative abundances of Coxiella and Rhodococcus increased. Ovarian transcriptional analysis revealed a cumulative effect of tetracycline treatment, as there was a significant increase in the number of differentially expressed genes with treatment time and a higher number of downregulated genes. The tick physiological pathways including lysosome, extracellular matrix (ECM)-receptor interaction, biosynthesis of ubiquinone and other terpenoids-quinones, insect hormone biosynthesis, and focal adhesion were significantly inhibited after 4 days of tetracycline treatment. Metabolite levels were altered after tetracycline treatment and the differences increased with treatment time. The differential metabolites were involved in a variety of physiological pathways; the downregulated metabolites were significantly enriched in the nicotinate and nicotinamide metabolism, galactose metabolism, and ether lipid metabolism pathways.

CONCLUSIONS

These findings indicate that tetracycline inhibits tick reproduction through the regulation of tick bacterial communities, gene expression and metabolic levels. The results may provide new strategies for tick control. © 2023 Society of Chemical Industry.

Does Leptinotarsa decemlineata larval survival after pesticide treatment depend on microbiome composition?

BACKGROUND

The microbiomes of some arthropods are believed to eliminate pesticides by chemical degradation or stimulation of the host immune system. The Colorado potato beetle (CPB; Leptinotarsa decemlineata) is an important agricultural pest with known resistance to used pesticides. We sought to analyze microbiome composition in CPB larvae from different sites and to identify the effect of pesticides on the microbiome of surviving and dead larvae after chlorpyrifos treatment in laboratory. Changes in the Lactococcus lactis community in larvae treated with chlorpyrifos and fed by potato leaves with L. lactis cover were studied by manipulative experiment. The microbiome was characterized by sequencing the 16S RNA gene.

RESULTS

The microbiome of L. decemlineata larvae is composed of a few operational taxonomic units (OTUs) (Enterobacteriaceae, Pseudocitrobacter, Acinetobacter, Pseudomonas, L. lactis, Enterococcus, Burkholderia and Spiroplasma leptinotarsae). The microbiome varied among the samples from eight sites and showed differences in profiles between surviving and dead larvae. The survival of larvae after chlorpyrifos treatment was correlated with a higher proportion of L. lactis sequences in the microbiome. The S. leptinotarsa profile also increased in the surviving larvae, but this OTU was not present in all sampling sites. In manipulative experiments, larvae treated with L. lactis had five-fold lower mortality rates than untreated larvae.

CONCLUSION

These results indicate that the microbiome of larvae is formed from a few bacterial taxa depending on the sampling site. A member of the gut microbiome, L. lactis, is believed to help overcome the toxic effects of chlorpyrifos in the larval gut. © 2023 Society of Chemical Industry.

Comparative metaproteomics reveal co-contribution of onion maggot and its gut microbiota to phoxim resistance

Pesticide resistance inflicts significant economic losses on a global scale each year. To address this pressing issue, substantial efforts have been dedicated to unraveling the resistance mechanisms, particularly the newly discovered microbiota-derived pesticide resistance in recent decades. Previous research has predominantly focused on investigating microbiota-derived pesticide resistance from the perspective of the pest host, associated microbes, and their interactions. However, a gap remains in the quantification of the contribution by the pest host and associated microbes to this resistance. In this study, we investigated the toxicity of phoxim by examining one resistant and one sensitive Delia antiqua strain. We also explored the critical role of associated microbiota and host in conferring phoxim resistance. In addition, we used metaproteomics to compare the proteomic profile of the two D. antiqua strains. Lastly, we investigated the activity of detoxification enzymes in D. antiqua larvae and phoxim-degrading gut microbes, and assessed their respective contributions to phoxim resistance in D. antiqua. The results revealed contributions by D. antiqua and its gut bacteria to phoxim resistance. Metaproteomics showed that the two D. antiqua strains expressed different protein profiles. Detoxifying enzymes including Glutathione S-transferases, carboxylesterases, Superoxide Dismutase, Glutathione Peroxidase, and esterase B1 were overexpressed in the resistant strain and dominated in differentially expressed insect proteins. In addition, organophosphorus hydrolases combined with a group of ABC type transporters were overexpressed in the gut microbiota of resistant D. antiqua compared to the sensitive strain. 85.2% variation of the larval mortality resulting from phoxim treatment could be attributed to the combined effects of proteins from both from gut bacteria and D. antiqua, while the individual contribution of proteins from gut bacteria or D. antiqua alone accounted for less than 10% of the variation in larval mortality caused by phoxim. The activity of the overexpressed insect enzymes and the phoxim-degrading activity of gut bacteria in resistant D. antiqua larvae were further confirmed. This work enhances our understanding of microbiota-derived pesticide resistance and illuminates new strategies for controlling pesticide resistance in the context of insect-microbe mutualism.

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 Effect of Residual Pesticide Application on Microbiomes of the Storage Mite Tyrophagus putrescentiae

Arthropods can host well-developed microbial communities, and such microbes can degrade pesticides and confer tolerance to most types of pests. Two cultures of the stored-product mite Tyrophagus putrescentiae, one with a symbiotic microbiome containing Wolbachia and the other without Wolbachia, were compared on pesticide residue (organophosphate: pirimiphos-methyl and pyrethroid: deltamethrin, deltamethrin + piperonyl butoxide)-containing diets. The microbiomes from mite bodies, mite feces and debris from the spent mite diet were analyzed using barcode sequencing. Pesticide tolerance was different among mite cultures and organophosphate and pyrethroid pesticides. The pesticide residues influenced the microbiome composition in both cultures but without any remarkable trend for mite cultures with and without Wolbachia. The most influenced bacterial taxa were Bartonella-like and Bacillus for both cultures and Wolbachia for the culture containing this symbiont. However, there was no direct evidence of any effect of Wolbachia on pesticide tolerance. The high pesticide concentration residues in diets reduced Wolbachia, Bartonella-like and Bacillus in mites of the symbiotic culture. This effect was low for Bartonella-like and Bacillus in the asymbiotic microbiome culture. The results showed that the microbiomes of mites are affected by pesticide residues in the diets, but the effect is not systemic. No actual detoxification effect by the microbiome was observed for the tested pesticides.

Spodoptera frugiperda (Lepidoptera: Noctuidae) Life Table Comparisons and Gut Microbiome Analysis Reared on Corn Varieties

The fall armyworm (Spodoptera frugiperda, FAW) is an invasive migratory pest that has recently spread to Korea, damaging several corn cultivars with significant economic value. Comparisons of the growth stages of FAW were conducted based on the preferred feed. Therefore, we selected six maize cultivars, including three categories: (i) commercial waxy corn (mibaek 2-ho, heukjeom 2-ho, dreamoak); (ii) popcorn (oryun popcorn, oryun 2-ho); and (iii) processing corn (miheukchal). A significant effect was observed during the larvae period, pupal period, egg hatching ratio, and larvae weight, whereas the total survival period and adult period did not show significant variation among the tested corn cultivars. We identified variations in the FAW gut bacterial community that were dependent on the genotype of the corn maize feed. The identified phyla included Firmicutes, Proteobacteria, Actinobacteria, and Bacteroidetes. Among these genera, the most abundant bacterial genus was Enterococcus, followed by Ureibacillus. Enterococcus mundtii was the most abundant among the top 40 bacterial species. The intergenic PCR-based amplification and gene sequence of the colony isolates were also matched to the GenBank owing to the prevalence of E. mundtii. These results showed that the bacterial diversity and abundance of particular bacteria in the guts of FAWs were influenced by the six major maize corn cultivars.

Ampicillin enhanced the resistance of Myzus persicae to imidacloprid and cyantraniliprole

BACKGROUND

Recent studies have shown that symbionts are involved in regulating insecticide detoxification in insects. However, there are few studies on the relationship between the symbionts found in Myzus persicae and the mechanism underlying host detoxification of insecticides. In this study, antibiotic ampicillin treatment was used to investigate the possible relationship between symbiotic bacteria and the detoxification of insecticides in the host, M. persicae.

RESULTS

Bioassays showed that ampicillin significantly reduced the susceptibilities of M. persicae to imidacloprid and cyantraniliprole. Synergistic bioassays and RNAi assays showed that the susceptibilities of M. persicae to imidacloprid and cyantraniliprole were related to metabolic detoxification enzyme activities and the expression level of the cytochrome P450 gene, CYP6CY3. Also, treatment to a combination of ampicillin and enzyme inhibitors or dsCYP6CY3 showed that the negative effect of ampicillin on the susceptibility of M. persicae was effectively inhibited bydetoxification enzyme inhibitors and dsCYP6CY3. Additionally, ampicillin treatment resulted in significant increases in the activities of multifunctional oxidases and esterases, the expression level of CYP6CY3 and fitness of M. persicae. Further, ampicillin significantly reduced the total bacterial abundance and changed symbiont diversity in M. persicae. The abundance of Pseudomonadaceae decreased significantly, while the abundance of Rhodococcus and Buchnera increased significantly.

CONCLUSION

Our study showed that ampicillin enhanced the resistance levels to imidacloprid and cyantraniliprole of M. persicae, which might be related to the selective elimination of symbiotic bacteria, the upregulated activities of detoxification enzymes and the increased fitness. © 2022 Society of Chemical Industry.

Vector microbiome: will global climate change affect vector competence and pathogen transmission?

Vector-borne diseases are among the greatest causes of human suffering globally. Several studies have linked climate change and increasing temperature with rises in vector abundance, and in the incidence and geographical distribution of diseases. The microbiome of vectors can have profound effects on how efficiently a vector sustains pathogen development and transmission. Growing evidence indicates that the composition of vectors' gut microbiome might change with shifts in temperature. Nonetheless, due to a lack of studies on vector microbiome turnover under a changing climate, the consequences for vector-borne disease incidence are still unknown. Here, we argue that climate change effects on vector competence are still poorly understood and the expected increase in vector-borne disease transmission might not follow a relationship as simple and straightforward as past research has suggested. Furthermore, we pose questions that are yet to be answered to enhance our current understanding of the effect of climate change on vector microbiomes, competence, and, ultimately, vector-borne diseases transmission.

Strain Tracking of 'Candidatus Liberibacter asiaticus', the Citrus Greening Pathogen, by High-Resolution Microbiome Analysis of Asian Citrus Psyllids

The Asian citrus psyllid, Diaphorina citri, is an invasive insect and a vector of 'Candidatus Liberibacter asiaticus' (CLas), a bacterium whose growth in Citrus species results in huanglongbing (HLB), also known as citrus greening disease. Methods to enrich and sequence CLas from D. citri often rely on biased genome amplification and nevertheless contain significant quantities of host DNA. To overcome these hurdles, we developed a simple pretreatment DNase and filtration (PDF) protocol to remove host DNA and directly sequence CLas and the complete, primarily uncultivable microbiome from D. citri adults. The PDF protocol yielded CLas abundances upward of 60% and facilitated direct measurement of CLas and endosymbiont replication rates in psyllids. The PDF protocol confirmed our lab strains derived from a progenitor Florida CLas strain and accumulated 156 genetic variants, underscoring the utility of this method for bacterial strain tracking. CLas genetic polymorphisms arising in lab-reared psyllid populations included prophage-encoding regions with key functions in CLas pathogenesis, putative antibiotic resistance loci, and a single secreted effector. These variants suggest that laboratory propagation of CLas could result in different phenotypic trajectories among laboratories and could confound CLas physiology or therapeutic design and evaluation if these differences remain undocumented. Finally, we obtained genetic signatures affiliated with Citrus nuclear and organellar genomes, entomopathogenic fungal mitochondria, and commensal bacteria from laboratory-reared and field-collected D. citri adults. Hence, the PDF protocol can directly inform agricultural management strategies related to bacterial strain tracking, insect microbiome surveillance, and antibiotic resistance screening.

Pesticide residue exposure provides different responses of the microbiomes of distinct cultures of the stored product pest mite Acarus siro

Background

The contribution of the microbiome to pesticide breakdown in agricultural pests remains unclear. We analyzed the effect of pirimiphos-methyl (PM) on four geographically different cultures of the stored product pest mite Acarus siro (6 L, 6Tu, 6Tk and 6Z) under laboratory experiments. The effect of PM on mite mortality in the impregnated filter paper test was compared.

Results

The mite sensitivity to PM decreased in the order of 6 L, 6Tu, 6Tk, and 6Z. Then, the mites were cultured on PM residues (0.0125 and 1.25 µg·g⁻¹), and population growth was compared to the control after 21 days of exposure. The comparison showed two situations: (i) increasing population growth for the most sensitive cultures (6 L and 6Tu), and (ii) no effect on mite population growth for tolerant cultures (6Z and 6Tk). The microbiome of mites was analyzed by quantification of 16S DNA copies based on quantitative polymerase chain reaction (qPCR) and by barcode sequencing of the V4 fragment of 16S DNA on samples of 30 individuals from the control and PM residues. The microbiome comprised primarily Solitalea-like organisms in all cultures, except for 6Z, followed by Bacillus, Staphylococcus, and Lactobacillus. The microbiomes of mite cultures did not change with increasing population density. The microbiome of cultures without any differences in population density showed differences in the microbiome composition. A Sodalis-like symbiont replaced Solitalea in the 1.25 µg·g⁻¹ PM in the 6Tk culture. Sodalis and Bacillus prevailed in the microbiomes of PM-treated mites of 6Z culture, while Solitalea was almost absent.

Conclusion

The results showed that the microbiome of A. siro differs in composition and in response to PM residues in the diet. The results indicate that Sodalis-like symbionts can help recover mites from pesticide-induced stress.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12866-022-02661-4.

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.

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.

Discovery of Early-Branching Wolbachia Reveals Functional Enrichment on Horizontally Transferred Genes

Wolbachia is a widespread endosymbiont of insects and filarial nematodes that profoundly influences host biology. Wolbachia has also been reported in rhizosphere hosts, where its diversity and function remain poorly characterized. The discovery that plant-parasitic nematodes (PPNs) host Wolbachia strains with unknown roles is of interest evolutionarily, ecologically, and for agriculture as a potential target for developing new biological controls. The goal of this study was to screen communities for PPN endosymbionts and analyze genes and genomic patterns that might indicate their role. Genome assemblies revealed 1 out of 16 sampled sites had nematode communities hosting a Wolbachia strain, designated wTex, that has highly diverged as one of the early supergroup L strains. Genome features, gene repertoires, and absence of known genes for cytoplasmic incompatibility, riboflavin, biotin, and other biosynthetic functions placed wTex between mutualist C + D strains and reproductive parasite A + B strains. Functional terms enriched in group L included protoporphyrinogen IX, thiamine, lysine, fatty acid, and cellular amino acid biosynthesis, while dN/dS analysis suggested the strongest purifying selection on arginine and lysine metabolism, and vitamin B6, heme, and zinc ion binding, suggesting these as candidate roles in PPN Wolbachia. Higher dN/dS pathways between group L, wPni from aphids, wFol from springtails, and wCfeT from cat fleas suggested distinct functional changes characterizing these early Wolbachia host transitions. PPN Wolbachia had several putative horizontally transferred genes, including a lysine biosynthesis operon like that of the mitochondrial symbiont Midichloria, a spirochete-like thiamine synthesis operon shared only with wCfeT, an ATP/ADP carrier important in Rickettsia, and a eukaryote-like gene that may mediate plant systemic acquired resistance through the lysine-to-pipecolic acid system. The Discovery of group L-like variants from global rhizosphere databases suggests diverse PPN Wolbachia strains remain to be discovered. These findings support the hypothesis of plant-specialization as key to shaping early Wolbachia evolution and present new functional hypotheses, demonstrating promise for future genomics-based rhizosphere screens.

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.

Synthesis and evaluation of novel xanthine-acrylamides and xanthine-acrylates as insecticidal agents

BACKGROUND

The design and discovery of novel pesticidal agents according to bioactive natural products is an important aspect of agrochemical innovation. New xanthine derivatives derived from natural xanthine or methylxanthines are rich resources that possess great potential to afford new active pesticidal molecules. Herein novel xanthine derivatives were designed through a strategy of combining the methylxanthine caffeine skeleton with the acrylamide or acrylate motif of cinnamic acid derivatives.

RESULTS

A series of novel (E)-3-(1,3,7-trimethyl-2,6-dioxo-2,3,6,7-tetrahydro-1H-purin-8-yl)acrylic acid derivatives, caffeine-(E)-acrylamides and caffeine-(E)-acrylates, were synthesized and confirmed via melting points, ¹ H NMR, ¹³ C NMR and high-resolution mass spectrometry. A single crystal of compound I12 was obtained to illustrate the trans-configuration of the vinyl double bond. Preliminary insecticidal evaluations showed that some of the compounds had favorable insecticidal potentials against Mythimna separata Walker at 200 mg L^-1 . Some of the compounds exhibited excellent insecticidal activity against Plutella xylostella L. at low test concentrations, e.g. I18 and I24 with LC₅₀ values of 0.0435 and 0.0133 mg L^-1 , respectively, were found to be more potent than the insecticide control triflumuron. The structure-activity relationship (SAR) analysis is also given in detail.

CONCLUSION

Compounds I12, I18, I24 and I26 generated from the integration of natural methylxanthine (caffeine) and acrylate moieties could be novel insecticidal leading compounds for further structural optimization. The SAR analysis may bring a new inspiration to the extensive and deep investigations on new xanthine derivatives in the agrochemical area.

Bacterial symbionts influence host susceptibility to fenitrothion and imidacloprid in the obligate hematophagous bed bug, Cimex hemipterus

The use of insecticides remains important in managing pest insects. Over the years, many insects manifested physiological and behavioral modifications resulting in reduced efficacy of insecticides targeted against them. Emerging evidence suggests that bacterial symbionts could modulate susceptibility of host insects against insecticides. Here, we explore the influence of host microbiota in affecting the susceptibility of insect host against different insecticides in the blood-sucking bed bug, Cimex hemipterus. Rifampicin antibiotic treatment resulted in increased susceptibility to fenitrothion and imidacloprid, but not against deltamethrin. Meanwhile, the host fitness parameters measured in the present study were not significantly affected by rifampicin treatment, suggesting the role of bacterial symbionts influencing susceptibility against the insecticides. 16S metagenomics sequencing revealed a drastic shift in the composition of several bacterial taxa following rifampicin treatment. The highly abundant Alphaproteobacteria (Wolbachia > 90%) and Gammaproteobacteria (Yersinia > 6%) in control bed bugs were significantly suppressed and replaced by Actinobacteria, Bacilli, and Betaproteobacteria in the rifampicin treated F1 bed bugs, suggesting possibilities of Wolbachia mediating insecticide susceptibility in C. hemipterus. However, no significant changes in the total esterase, GST, and P450 activities were observed following rifampicin treatment, indicating yet unknown bacterial mechanisms explaining the observed phenomena. Re-inoculation of microbial content from control individuals regained the tolerance of rifampicin treated bed bugs to imidacloprid and fenitrothion. This study provides a foundation for a symbiont-mediated mechanism in influencing insecticide susceptibility that was previously unknown to bed bugs.

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.

Mosquito-Associated Viruses and Their Related Mosquitoes in West Africa

Mosquito-associated viruses (MAVs), including mosquito-specific viruses (MSVs) and mosquito-borne (arbo)viruses (MBVs), are an increasing public, veterinary, and global health concern, and West Africa is projected to be the next front for arboviral diseases. As in-depth knowledge of the ecologies of both western African MAVs and related mosquitoes is still limited, we review available and comprehensive data on their diversity, abundance, and distribution. Data on MAVs’ occurrence and related mosquitoes were extracted from peer-reviewed publications. Data on MSVs, and mosquito and vertebrate host ranges are sparse. However, more data are available on MBVs (i.e., dengue, yellow fever, chikungunya, Zika, and Rift Valley fever viruses), detected in wild and domestic animals, and humans, with infections more concentrated in urban areas and areas affected by strong anthropogenic changes. Aedes aegypti, Culex quinquefasciatus, and Aedes albopictus are incriminated as key arbovirus vectors. These findings outline MAV, related mosquitoes, key knowledge gaps, and future research areas. Additionally, these data highlight the need to increase our understanding of MAVs and their impact on host mosquito ecology, to improve our knowledge of arbovirus transmission, and to develop specific strategies and capacities for arboviral disease surveillance, diagnostic, prevention, control, and outbreak responses in West Africa.

Differences in the intestinal microbiota between insecticide-resistant and -sensitive Aedes albopictus based on full-length 16S rRNA sequencing

The intestinal symbiotic bacteria of Aedes albopictus play a potential role in host resistance to insecticides. In this study, we sequenced the full‐length of 16S rRNA and analyzed the differences in the intestinal microbiota between deltamethrin‐resistant and ‐sensitive Ae. albopictus. Symbiotic bacteria were cultured and analyzed using six types of culture media in aerobic and anaerobic environments. We found significant differences in the diversity and abundance of the intestinal microbiota of the two strains of Ae. albopictus. The symbiotic bacteria cultured in vitro were found to be mainly facultative anaerobes. The cultured bacteria such as Serratia oryzae and Acinetobacter junii may function to promote the development of insecticide resistance. This work indicates that intestinal bacteria may contribute to the enhancement of insecticide resistance of Ae. albopictus It also highlights the analytical advantage of full‐length 16S rRNA sequencing to study the intestinal microbiota of mosquitoes.

Host resistance to Bacillus thuringiensis is linked to altered bacterial community within a specialist insect herbivore

Evolution of resistance to transgenic crops producing toxins from Bacillus thuringiensis (Bt) threatens the sustainability of the technology. Examination of resistance mechanisms has largely focused on characterization of mutations in proteins serving as Bt toxin binding sites. However, insect microbial communities have the potential to provide host resistance to pesticides in a myriad of ways. Previous findings suggest the killing mechanism of Bt relies on enteric bacteria becoming pathogenic in the disrupted gut environment of the insect following Bt intoxication. Thus, here we hypothesized that resistance to Bt would alter the microbiome composition of the insect. Previous studies have manipulated the microbiome of susceptible insects and monitored their response to Bt. In our study, we characterized the associated bacterial communities of Bt‐resistant and ‐susceptible western corn rootworms, a widespread pest of maize in the United States. We found resistant insects harbor a bacterial community that is less rich and distinct from susceptible insects. After feeding on Bt‐expressing maize, susceptible insects exhibited dysbiosis of the associated bacterial community, whereas the community within resistant insects remained relatively unchanged. These results suggest resistance to Bt produces alterations in the microbiome of the western corn rootworm that may contribute to resistance. We further demonstrated that by itself, feeding on Bt toxin‐expressing seedlings caused a shift in the microbiota. This work provides a broader picture of the effect stressors have on microbiome composition, and the potential heritable changes induced as a result of intense selection.

New Insights into Cockroach Control: Using Functional Diversity of Blattella germanica Symbionts

Simple Summary

Insect hosts have close relationships with microbial symbionts. The limited metabolic networks of most insects are enhanced by these symbiotic relationships. Using symbiotic microorganisms for biological control of insects and insect-borne diseases has become an important research topic and shows potential for the development of applicable control approaches. Blattella germanica (L.) is public health pest worldwide; it is difficult to control because of its strong reproductive ability, adaptability, and resistance to insecticides. In this paper, the diverse biological functions (nutrition metabolism, reproductive regulation, insecticide resistance, defense, and behavior management) of symbionts, their interaction mechanism with hosts, and the research progress in the control of B. germanica are reviewed and discussed.

Abstract

Insects have close symbiotic relationships with several microbes, which extends the limited metabolic networks of most insects. Using symbiotic microorganisms for the biological control of pests and insect-borne diseases has become a promising direction. Blattella germanica (L.) (Blattaria: Blattidae) is a public health pest worldwide, which is difficult to control because of its strong reproductive ability, adaptability, and resistance to insecticides. In this paper, the diverse biological functions (nutrition, reproductive regulation, insecticide resistance, defense, and behavior) of symbionts were reviewed, and new biological control strategies on the basis of insect–symbiont interaction were proposed. We highlight new directions in B. germanica control, such as suppressing cockroach population using Wolbachia or paratransgenes, and combining fungal insecticides with synergistic agents to enhance insecticidal efficacy.

Gut bacteria of the silkworm Bombyx mori facilitate host resistance against the toxic effects of organophosphate insecticides

Organophosphate insecticides that are heavily used in agriculture for pest control have caused growing environmental problems and public health concerns worldwide. Ironically, insecticide resistance develops quickly in major lepidopteran pests, partially via their microbial symbionts. To investigate the possible mechanisms by which the microbiota confers insecticide resistance to Lepidoptera, the model organism silkworm Bombyx mori (Lepidoptera: Bombycidae) was fed different antibiotics to induce gut dysbiosis (microbiota imbalance). Larvae treated with polymyxin showed a significantly lower survival rate when exposed to chlorpyrifos. Through high-throughput sequencing, we found that the abundances of Stenotrophomonas and Enterococcus spp. changed substantially after treatment. To assess the roles played by these two groups of bacteria in chlorpyrifos resistance, a germ-free (GF) silkworm rearing protocol was established to avoid the influence of natural microbiota and antibiotics. Monoassociation of GF silkworms with Stenotrophomonas enhanced host resistance to chlorpyrifos, but not in Enterococcus-fed larvae, consistent with larval detoxification activity. GC-μECD detection of chlorpyrifos residues in feces indicated that neither Stenotrophomonas nor Enterococcus degraded chlorpyrifos directly in the gut. However, gut metabolomics analysis revealed a highly species-specific pattern, with higher levels of essential amino acid produced in the gut of silkworm larvae monoassociated with Stenotrophomonas. This critical nutrient provisioning significantly increased host fitness and thereby allowed larvae to circumvent the deleterious effects of these toxic chemicals more efficiently. Altogether, our study not only suggests a new mechanism for insecticide resistance in notorious lepidopteran pests but also provides a useful template for investigating the interplay between host and gut bacteria in complex environmental systems.

Disentangling of the ecotoxicological signal using "omics" analyses, a lesson from the survey of the impact of cyanobacterial proliferations on fishes

Omics technologies offer unprecedented perspectives for the rational investigation of complex biological systems. Indeed, omics present the ability of offering an extensive perception of the biochemistry and physiology of the cell and of any perturbing consequences of contaminants through the joint investigation of thousands of molecular responses simultaneously; then it has recently conducted to a fervent attention by research ecotoxicologists. Beyond the presentation of latest advances, exemplified here by omics investigation of cyanobacterial deleterious effects on various fishes (at various experimental and biological scales and with various analytical tools and pipeline), the present review paper re-explores the promising perspectives and also the pitfalls of such holistic investigations of the ecotoxicological response of organisms for environmental assessment.

Perspective: root exudation of herbicides as a novel mode of herbicide resistance in weeds

The evolution of resistance to herbicides in weeds has become a great challenge for global agricultural production. Weeds have evolved resistance to herbicides through many different physiological mechanisms. Some weed species are known to secrete herbicide molecules from roots into the rhizosphere upon being treated. However, root exudation of herbicides as a mechanism of resistance has only recently been identified in two weed species. Root exudation pathways have been investigated in Arabidopsis, and this work suggested that ATP-binding cassette (ABC) and multidrug and toxic compound extrusion (MATE) transporters play a role in the secretion of primary and secondary plant products from roots. We hypothesize that the mechanisms involved in root exudation of herbicides that result in resistance are mediated by overactive or overexpressed transporters, probably similar to those found for the exudation of primary and secondary compounds from roots. Elucidating the molecular and physiological basis of root exudation in herbicide-resistant weeds would improve our understanding of the pathways involved in herbicide root secretion mediated by transporters in plants. © 2020 Society of Chemical Industry.

Biodegradation of recalcitrant compounds and phthalates by culturable bacteria isolated from Liometopum apiculatum microbiota

Liometopum apiculatum is a species of ants widely distributed in arid and semi-arid ecosystems where there is a relative food shortage compared with tropical ecosystems. L. apiculatum has established an ecological balance involving symbiotic interactions, which have allowed them to survive through mechanisms that are still unknown. Therefore, the aim of this study was to explore the metabolic potential of isolated bacteria from L. apiculatum using enzymatic activity assay and substrate assimilation. Results revealed a complex bacteria consortium belonging to Proteobacteria, Firmicutes, and Actinobacteria phylum. Most of the isolated bacteria showed activities associated with biopolymers degradation, from them Exiguobacterium and B. simplex showed the highest amylolytic activity (27 U/mg protein), while A. johnsonii and B. pumulis showed the highest cellulolytic and xylanolytic activities (1 and 2.9 U/mg protein, respectively). By other hand, some microorganisms such as S. ficaria, E. asburiae, P. agglomerans, A. johnsonii, S. rubidaea, S. marcescens, S. warneri, and M. hydrocarbonoxydans were able to grow up to 1000 mg/L of phthalates esters. These results not only revealed the important contribution of the symbionts in L apiculatum ants feeding habits, but also have shown a promising source of enzymes with potential biotechnological applications such as lignocellulosic biomass hydrolysis and bioremediation processes.

Gut microbiota metabolic potential correlates with body size between mulberry-feeding lepidopteran pest species

BACKGROUND

Many insect pests rely on microbial symbionts to obtain nutrients or for defence, thereby allowing them to exploit novel food sources and degrade environmental xenobiotics, including pesticides. Although Lepidoptera is one of the most diverse insect taxa and includes important agricultural pests, lepidopteran microbiotas, particularly functional traits, have not been studied widely. Here, we provide a comprehensive characterization of the gut microbiota across multiple mulberry-feeding lepidopteran species, resolving both community structure and metabolic potential.

RESULTS

Our results indicate abundant bacteria inside the gut of larval Lepidoptera. However, even though they were fed the same diet, the structures of the bacterial communities differed in four major mulberry pest species, suggesting host-specific effects on microbial associations. Community-level metabolic reconstructions further showed that although taxonomic composition varied greatly, carbohydrate and amino acid metabolism and membrane transporter were key functional capabilities of the gut bacteria in all samples, which may play basic roles in the larval gut. In addition, principal coordinate analysis (PCoA) of gut bacterial-predicted gene ontologies revealed specialized features of the microbiota associated with these mulberry pests, which were divided into two distinct clusters (macrolepidopterans and microlepidopterans). This pattern became even more prominent when further Lepidoptera species were involved.

CONCLUSIONS

A suite of gut microbiota metabolic functions significantly correlated with larval size; the metabolism of terpenoids and polyketides, xenobiotics biodegradation and metabolism were specifically enriched in large species, while small larvae had enhanced nucleotide metabolism. Our report paves the way for uncovering the correlation between host phenotype and microbial symbiosis in this notorious insect pest group. © 2019 Society of Chemical Industry.

Host determinants of among-species variation in microbiome composition in drosophilid flies

The taxonomic composition of microbial communities in animals varies among animal species, but the contribution of interspecific differences in filtering of the microbial pool by the animal host to this variation is uncertain. Here, we demonstrate significant interspecific variation in microbial community composition among laboratory-reared Drosophila species that was not related to host phylogeny. Complementary reciprocal transfer experiments yielded different microbial communities for a single microbiota administered to homologous and heterologous hosts (i.e., the same and different Drosophila species from which the microbiota was derived), indicative of among-host species differences in traits that shape microbiota composition. The difference in microbiota composition between homologous and heterologous hosts was not greater for distantly related than for closely related host species pairs. Furthermore, Drosophila survival to adulthood was significantly reduced in heterologous associations relative to homologous associations and microbiologically sterile flies, suggesting that microbial taxa that are advantageous for their homologous host species can be deleterious for other host species. We conclude that drosophilid flies display robust among-host species variation in host controls over microbiota composition that has diversified in response to selection pressures which are not tracked by host phylogeny.

Implication of human drug transporters to toxicokinetics and toxicity of pesticides

Human membrane drug transporters are recognized as major actors of pharmacokinetics. Pesticides also interact with human drug transporters, which may have consequences for pesticide toxicokinetics and toxicity. The present review summarizes key findings about this topic. In vitro assays have demonstrated that some pesticides, belonging to various chemical classes, modulate drug transporter activity, regulate transporter expression and/or are substrates, thus bringing the proof of concept for pesticide-transporter relationships. The expected low human concentration of pesticides in response to environmental exposure constitutes a key-parameter to be kept in mind for judging the in vivo relevance of such pesticide-transporter interactions and their consequences for human health. Existing data about interactions of pesticides with drug transporters remain, however, rather sparse; more extensive and systematic characterization of pesticide-transporter relationships, through the use of high throughput in vitro assays and/or in silico methods, is, therefore, required. In addition, consideration of transporter polymorphisms, pesticide mixture effects and physiological and pathological factors governing drug transporter expression may help to better define the in vivo relevance of pesticide-transporter interactions in terms of toxicokinetics and toxicity for humans. © 2019 Society of Chemical Industry.

Life history and functional capacity of the microbiome are altered in beta-cypermethrin-resistant cockroaches

Cockroaches are widely perceived to evolve resistance to insecticides. Over-expression of a resistance-conferring gene can be costly and may require energy and resource reallocation for metabolic and developmental processes. To evaluate whether changes in the composition of gut microbiota in Blattella germanica affected its resistance evolution to beta-cypermethrin and to determine the role of gut microbiota in host growth and development, we studied the relationship between insecticide resistance and the diversity and genetic content of gut microbiota in cockroaches. Results suggest beta-cypermethrin-resistant cockroaches (R strain) exhibited a delayed development period and reduced adult longevity compared with susceptible cockroaches (S strain). Based on 16S rRNA gene sequencing and community metagenomics, we found that the relative abundance of Lactobacillus and Acetobacteraceae were significantly lower in the R strain compared with the S strain in the foregut and midgut of both strains. Functional annotation of Kyoto Encyclopedia of Genes and Genomes (KEGG) modules of midgut genes in the two strains revealed that 10.6% were involved in metabolism, while the relative abundance in the R strain was 7.4%. Unigenes were also translated into amino acid sequences and assigned to protein families based on hits to the Carbohydrate-Active enzymes (CAZy) database. This process identified the glycoside hydrolases, glycosyl transferases and carbohydrate-binding modules of the S strain as all being significantly higher in diversity than those in the R strain. Overall, we conclude that fitness-related costs increased in the resistant strain of cockroaches compared with the susceptible strain, and the variation in insect gut microbiota, especially those related to growth and development, was an important influencing factor.

Parasitoid envenomation alters the Galleria mellonella midgut microbiota and immunity, thereby promoting fungal infection

Gut bacteria influence the development of different pathologies caused by bacteria, fungi and parasitoids in insects. Wax moth larvae became more susceptible to fungal infections after envenomation by the ectoparasitoid Habrobracon hebetor. In addition, spontaneous bacterioses occurred more often in envenomated larvae. We analyzed alterations in the midgut microbiota and immunity of the wax moth in response to H. hebetor envenomation and topical fungal infection (Beauveria bassiana) alone or in combination using 16S rRNA sequencing, an analysis of cultivable bacteria and a qPCR analysis of immunity- and stress-related genes. Envenomation led to a predominance shift from enterococci to enterobacteria, an increase in CFUs and the upregulation of AMPs in wax moth midguts. Furthermore, mycosis nonsignificantly increased the abundance of enterobacteria and the expression of AMPs in the midgut. Combined treatment led to a significant increase in the abundance of Serratia and a greater upregulation of gloverin. The oral administration of predominant bacteria (Enterococcus faecalis, Enterobacter sp. and Serratia marcescens) to wax moth larvae synergistically increased fungal susceptibility. Thus, the activation of midgut immunity might prevent the bacterial decomposition of envenomated larvae, thus permitting the development of fungal infections. Moreover, changes in the midgut bacterial community may promote fungal killing.

Interaction of Chemical Pesticides and Their Formulation Ingredients with Microbes Associated with Plants and Plant Pests

Chemical pesticides and their formulation ingredients can have unintended effects on microbes associated with plants and plant pests. These effects can be due to direct effects on the microbes or to effects on crops or weeds that subsequently affect the microbes. In addition to fungicides, some insecticides, herbicides, and formulation compounds are toxic to plant pathogenic microbes, as well as to potentially beneficial microbes, such as those that infect insect pests. These chemicals, especially herbicides, can also indirectly affect microbes through their effects on crops and weeds. For example, glyphosate strongly impairs shikimic acid pathway-based plant defenses to microbial diseases in glyphosate-susceptible plants, significantly increasing its efficacy as an herbicide. Some herbicides induce plant defenses against plant pathogens. For a complete understanding of integrated pest management and overall cost/benefit of pesticide use, much more information is needed on microbial/pesticide interactions.

Predicting mammalian metabolism and toxicity of pesticides in silico

Pesticides must be effective to be commercially viable but they must also be reasonably safe for those who manufacture them, apply them, or consume the food they are used to produce. Animal testing is key to ensuring safety, but it comes late in the agrochemical development process, is expensive, and requires relatively large amounts of material. Surrogate assays used as in vitro models require less material and shift identification of potential mammalian toxicity back to earlier stages in development. Modern in silico methods are cost-effective complements to such in vitro models that make it possible to predict mammalian metabolism, toxicity and exposure for a pesticide, crop residue or other metabolite before it has been synthesized. Their broader use could substantially reduce the amount of time and effort wasted in pesticide development. This contribution reviews the kind of in silico models that are currently available for vetting ideas about what to synthesize and how to focus development efforts; the limitations of those models; and the practical considerations that have slowed development in the area. Detailed discussions are provided of how bacterial mutagenicity, human cytochrome P450 (CYP) metabolism, and bioavailability in humans and rats can be predicted. © 2018 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.