Actinomycetes are a natural resource for sustainable pest control and safeguarding agriculture.

Actinomycetes, a diverse group of bacteria with filamentous growth characteristics, have long captivated researchers and biochemists for their prolific production of secondary metabolites. Among the myriad roles played by actinomycete secondary metabolites, their historical significance in the field of biocontrol stands out prominently. The fascinating journey begins with the discovery of antibiotics, where renowned compounds like streptomycin, tetracycline, and erythromycin revolutionized medicine and agriculture. The history of biocontrol traces its roots back to the early twentieth century, when scientists recognized the potential of naturally occurring agents to combat pests and diseases. The emergence of synthetic pesticides in the mid-twentieth century temporarily overshadowed interest in biocontrol. However, with growing environmental concerns and the realization of the negative ecological impacts of chemical pesticides, the pendulum swung back towards exploring sustainable alternatives. Beyond their historical role as antibiotics, actinomycete-produced secondary metabolites encompass a rich repertoire with biopesticide potential. The classification of these compounds based on chemical structure and mode of action is highlighted, demonstrating their versatility against both plant pathogens and insect pests. Additionally, this review provides in-depth insights into how endophytic actinomycete strains play a pivotal role in biocontrol strategies. Case studies elucidate their effectiveness in inhibiting Spodoptera spp. and nematodes through the production of bioactive compounds. By unraveling the multifunctional roles of endophytic actinomycetes, this review contributes compelling narrative knowledge to the field of sustainable agriculture, emphasizing the potential of these microbial allies in crafting effective, environmentally friendly biocontrol strategies for combating agricultural pests.

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.

Study on the virulence of Metarhizium anisopliae against Spodoptera frugiperda (J. E. Smith, 1797).

This study examined the impact of Metarhizium anisopliae (Hypocreales: Clavicipitaceae) conidia on the eggs, larvae, pupae, and adults of Spodoptera frugiperda. The results showed that eggs, larvae, pupae, and adults exhibited mortality rates that were dependent on the dose. An increased amount of conidia (1.5 × 109 conidia/mL) was found to be toxic to larvae, pupae, and adults after 9 days of treatment, resulting in a 100% mortality rate in eggs, 98% in larvae, 76% in pupae, and 85% in adults. A study using earthworms as bioindicators found that after 3 days of exposure, M. anisopliae conidia did not cause any harmful effects on the earthworms. In contrast, the chemical treatment (positive control) resulted in 100% mortality at a concentration of 40 ppm. Histopathological studies showed that earthworm gut tissues treated with fungal conidia did not show significant differences compared with those of the negative control. The gut tissues of earthworms treated with monocrotophos exhibited significant damage, and notable differences were observed in the chemical treatment. The treatments with 70 and 100 µg/mL solutions of Eudrilus eugeniae epidermal mucus showed no fungal growth. An analysis of the enzymes at a biochemical level revealed a decrease in the levels of acetylcholinesterase, α-carboxylesterase, and ß-carboxylesterase in S. frugiperda larvae after exposure to fungal conidia. This study found that M. anisopliae is effective against S. frugiperda, highlighting the potential of this entomopathogenic fungus in controlling this agricultural insect pest.

Gut dysbacteriosis induces expression differences in the adult head transcriptome of Spodoptera frugiperda in a sex-specific manner.

Mounting evidence indicates that the gut microbiota influences the neurodevelopment and behavior of insects through the gut-brain axis. However, it is currently unclear whether the gut microbiota affect the head profiles and immune pathway in pests. Here, we find that gut bacteria is essential for the immune and neural development of adult Spodoptera frugiperda, which is an extremely destructive agricultural pest worldwide. 16 S rRNA sequencing analysis showed that antibiotics exposure significantly disturbed the composition and diversity of gut bacteria. Further transcriptomic analysis revealed that the adult head transcripts were greatly affected by gut dysbacteriosis, and differently expression genes critical for brain and neural development including A4galt, Tret1, nsun4, Galt, Mitofilin, SLC2A3, snk, GABRB3, Oamb and SLC6A1 were substantially repressed. Interestingly, the dysbacteriosis caused sex-specific differences in immune response. The mRNA levels of pll (serine/threonine protein kinase Pelle), PGRP (peptidoglycan-sensing receptor), CECA (cecropin A) and CECB (cecropin B) involved in Toll and Imd signaling pathway were drastically decreased in treated male adults' heads but not in female adults; however, genes of HIVEP2, ZNF131, inducible zinc finger protein 1-like and zinc finger protein 99-like encoding zinc-finger antiviral protein (ZAP) involved in the interferon (IFNα/ß) pathway were significantly inhibited in treated female adults' heads. Collectively, these results demonstrate that gut microbiota may regulate head transcription and impact the S. frugiperda adults' heads through the immune pathway in a sex-specific manner. Our finding highlights the relationship between the gut microbiota and head immune systems of S. frugiperda adults, which is an astonishing similarity with the discoveries of other animals. Therefore, this is the basis for further research to understand the interactions between hosts and microorganisms via the gut-brain axis in S. frugiperda and other insects.

The Adaptive Evolution in the Fall Armyworm Spodoptera frugiperda (Lepidoptera: Noctuidae) Revealed by the Diversity of Larval Gut Bacteria.

Insect gut microbes have important roles in host feeding, digestion, immunity, development, and coevolution with pests. The fall armyworm, Spodoptera frugiperda (Smith, 1797), is a major migratory agricultural pest worldwide. The effects of host plant on the pest's gut bacteria remain to be investigated to better understand their coevolution. In this study, differences in the gut bacterial communities were examined for the fifth and sixth instar larvae of S. frugiperda fed on leaves of different host plants (corn, sorghum, highland barley, and citrus). The 16S rDNA full-length amplification and sequencing method was used to determine the abundance and diversity of gut bacteria in larval intestines. The highest richness and diversity of gut bacteria were in corn-fed fifth instar larvae, whereas in sixth instar larvae, the richness and diversity were higher when larvae were fed by other crops. Firmicutes and Proteobacteria were dominant phyla in gut bacterial communities of fifth and sixth instar larvae. According to the LDA Effect Size (LEfSe) analysis, the host plants had important effects on the structure of gut bacterial communities in S. frugiperda. In the PICRUSt2 analysis, most predicted functional categories were associated with metabolism. Thus, the host plant species attacked by S. frugiperda larvae can affect their gut bacterial communities, and such changes are likely important in the adaptive evolution of S. frugiperda to host plants.

Sources of Fungal Symbionts in the Microbiome of a Mobile Insect Host, Spodoptera frugiperda.

The sources of fungal symbionts of insects are not well understood, yet the acquisition and assembly of fungal communities in mobile insect hosts have important implications for the ecology of migratory insects and their plant hosts. To determine potential sources of fungi associated with the fall armyworm (Spodoptera frugiperda), we characterized the fungal communities associated with four different ecological compartments (insects, infested leaves, uninfested leaves, and soil) and estimated the contributions of each of these potential sources to the insect's fungal microbiome. Results show that insect fungal community composition was distinct from and more varied than the composition of fungal communities in the environment of those insects (plants and soil). Among the sources evaluated, on average we found a surprisingly large apparent contribution from other congeneric S. frugiperda insect larvae (ca. 25%) compared to the contribution from soil or plant sources (< 5%). However, a large proportion of the insect microbiome could not be attributed to the sampled sources and was instead attributed to unknown sources (ca. 50%). Surprisingly, we found little evidence for exchange of fungal taxa, with the exception of a Fusarium oxysporum and a Cladosporium sp. OTU, between larvae and the infested leaves on which they fed. Together, our results suggest that mobile insects such as S. frugiperda obtain their fungal symbionts from a variety of sources, not limited to plants and soil, but including conspecific insects and other unsampled environmental sources, and that transmission among insects may play an important role in acquisition of fungal symbionts.

Gut microbial community supplementation and reduction modulates African armyworm susceptibility to a baculovirus.

Gut microbiota stimulates the immune system and inhibits pathogens, and thus, it is critical for disease prevention. Probiotics represent an effective alternative to antibiotics used for the therapy and prevention of bacterial diseases. Probiotic bacteria are commonly used in vertebrates, although their use in invertebrates is still rare. We manipulated the gut microbiome of the African Armyworm (Spodoptera exempta Walker) using antibiotics and field-collected frass, in an attempt to understand the interactions of the gut microbiome with the nucleopolyhedrovirus, SpexNPV. We found that S. exempta individuals with supplemented gut microbiome were significantly more resistant to SpexNPV, relative to those with a typical laboratory gut microbiome. Illumina MiSeq sequencing revealed the bacterial phyla in the S. exempta gut belonged to 28 different classes. Individuals with an increased abundance of Lactobacillales had a higher probability of surviving viral infection. In contrast, there was an increased abundance of Enterobacteriales and Pseudomonadales in individuals dying from viral infection, corresponding with decreased abundance of these two Orders in surviving caterpillars, suggesting a potential role for them in modulating the interaction between the host and its pathogen. These results have important implications for laboratory studies testing biopesticides.

Identification of entomopathogenic fungus Metarhizium rileyi infested in fall armyworm in the cornfield of Korea, and evaluation of its virulence.

The fall armyworm (FAW) Spodoptera frugiperda is an important invasive pest in Africa and Asia. It is a polyphagous pest with at least 353 recorded host plant species, including corn. Chemical control of this pest is unsuccessful because of a developed resistance and harmful effects on the environment. Entomopathogenic fungi are potential biological control agents for FAW. In this study, the native strain of Metarhizium rileyi (KNU-Ye-1), collected from a cornfield at Yeongcheon, Korea, was identified by morphological and molecular characterization. The susceptibility of the fourth-instar larvae of FAW to the native strain M. rileyi was examined in the laboratory. The results showed that the Korean strain of M. rileyi (KNU-Ye-1) was highly virulent to FAW larvae, causing 89% mortality 7 days posttreatment. Therefore, M. rileyi (KNU-Ye-1) identified in this study is highly valuable for the biological control of FAW in the field.

Host-Specific larval lepidopteran mortality to pathogenic Serratia mediated by poor diet.

Insect guts often harbor an abundance of bacteria. Many of these members are commensal, but some may emerge as opportunistic pathogens when the host is under stress. In this study, we evaluated how dietary nutritional concentration mediates a shift from commensal to pathogenic, and if host species influences those interactions. We used the lepidopterans (Noctuidae) fall armyworm (Spodoptera frugiperda), beet armyworm (Spodoptera exigua), and corn earworm (Helicoverpa zea) as hosts and a Serratia strain initially isolated from healthy fall armyworm. Diet concentration was altered by bulk reduction in nutritional content with dilution using cellulose. Our experiments revealed that low nutrient diet increased mortality from Serratia for beet armyworm and corn earworm. However, for fall armyworm, little mortality was observed in any of the diet combinations. Dietary nutrition and oral inoculation with Serratia did not change the expression of two antimicrobial peptides in fall and beet armyworm, suggesting that other mechanisms that mediate mortality were involved. Our results have implications for how pathogens may persist as commensals in the digestive tract of insects. These findings also suggest that diet plays a very important role in the switch from commensal to pathogen. Finally, our data indicate that the host response to changing conditions is critical in determining if a pathogen may overtake its host and that these three lepidopteran species have different responses to opportunistic enteric pathogens.

The bacterial and fungal communities of the larval midgut of Spodoptera frugiperda (Lepidoptera: Noctuidae) varied by feeding on two cruciferous vegetables.

Spodoptera frugiperda is a highly polyphagous pest worldwide with a wide host range that causes serious losses to many economically important crops. Recently, insect-microbe associations have become a hot spot in current entomology research, and the midgut microbiome of S. frugiperda has been investigated, while the effects of cruciferous vegetables remain unknown. In this study, the growth of S. frugiperda larvae fed on an artificial diet, Brassica campestris and Brassica oleracea for 7 days was analyzed. Besides, the microbial community and functional prediction analyses of the larval midguts of S. frugiperda fed with different diets were performed by high-throughput sequencing. Our results showed that B. oleracea inhibited the growth of S. frugiperda larvae. The larval midgut microbial community composition and structure were significantly affected by different diets. Linear discriminant analysis effect size (LEfSe) suggested 20 bacterial genera and 2 fungal genera contributed to different gut microbial community structures. The functional classification of the midgut microbiome analyzed by PICRUSt and FUNGuild showed that the most COG function categories of midgut bacterial function were changed by B. oleracea, while the guilds of fungal function were altered by B. campestris significantly. These results showed that the diversity and structure of the S. frugiperda midgut microbial community were affected by cruciferous vegetable feeding. Our study provided a preliminary understanding of the role of midgut microbes in S. frugiperda larvae in response to cruciferous vegetables.

Opposing Growth Responses of Lepidopteran Larvae to the Establishment of Gut Microbiota.

Gut microbiota can have diverse impacts on hosts, the nature of which often depend on the circumstances. For insect gut microbes, the quality and nature of host diets can be a significant force in swinging the pendulum from inconsequential to functionally important. In our study, we addressed whether beneficial microbes in one species impart similar functions to related species under identical conditions. Using fall armyworm (Spodoptera frugiperda), beet armyworm (Spodoptera exigua), and other noctuid hosts, we implemented an axenic rearing strategy and manipulated gut bacterial populations and dietary conditions. Our results revealed that some gut Enterococcus and Enterobacter isolates can facilitate utilization of a poor diet substrate by fall armyworm, but this was not the case for other more optimized diets. While Enterococcus provided benefits to fall armyworm, it was decidedly antagonistic to beet armyworm (Spodoptera exigua) under identical conditions. Unique isolates and bacterial introductions at early growth stages were critical to how both larval hosts performed. Our results provide robust evidence of the roles in which bacteria support lepidopteran larval growth, but also indicate that the directionality of these relationships can differ among congener hosts. IMPORTANCE Insects have intimate relationships with gut microbiota, where bacteria can contribute important functions to their invertebrate hosts. Lepidopterans are important insect pests, but how they engage with their gut bacteria and how that translates to impacts on the host are lacking. Here we demonstrate the facultative nature of gut microbiota in lepidopteran larvae and the importance of diet in driving mutualistic or antagonistic relationships. Using multiple lepidopteran species, we uncover that the same bacteria that can facilitate exploitation of a challenging diet in one host severely diminishes larval performance of another larval species. Additionally, we demonstrate the beneficial functions of gut microbiota on the hosts are not limited to one lineage, but rather multiple isolates can facilitate the exploitation of a suboptimal diet. Our results illuminate the context-dependent nature of the gut microbiomes in invertebrates, and how host-specific microbial engagement can produce dramatically different interactions.

An Integrative Analysis of Transcriptomics and Proteomics Reveals Novel Insights into the Response in the Midgut of Spodoptera frugiperda Larvae to Vip3Aa.

The insecticidal Vip3 proteins, secreted by Bacillus thuringiensis (Bt) during its vegetative growth phase, are currently used in Bt crops to control insect pests, and are genetically distinct from known insecticidal Cry proteins. Compared with Cry toxins, the mechanisms of Vip3 toxins are still poorly understood. Here, the responses of Spodoptera frugiperda larvae after Vip3Aa challenge are characterized. Using an integrative analysis of transcriptomics and proteomics, we found that Vip3Aa has enormous implications for various pathways. The downregulated genes and proteins were mainly enriched in metabolic pathways, including the insect hormone synthesis pathway, whereas the upregulated genes and proteins were mainly involved in the caspase-mediated apoptosis pathway, along with the MAPK signaling and endocytosis pathways. Moreover, we also identified some important candidate genes involved in apoptosis and MAPKs. The present study shows that exposure of S. frugiperda larvae to Vip3Aa activates apoptosis pathways, leading to cell death. The results will promote our understanding of the host response process to the Vip3Aa, and help us to better understand the mode of action of Vip3A toxins.

Toll signal pathway activating eicosanoid biosynthesis shares its conserved upstream recognition components in a lepidopteran Spodoptera exigua upon infection by Metarhizium rileyi, an entomopathogenic fungus.

Eicosanoids play crucial roles in mediating immune responses in insects. Upon a fungal infection, Toll signal pathway can mediate immune responses of Spodoptera exigua, a lepidopteran insect, by activating eicosanoid biosynthesis. However, upstream signal components of the Toll signal pathway activating eicosanoid biosynthesis remain unclear. This study predicted pattern recognition receptors (PRRs) and serine proteases (SPs) as upstream components of the Toll pathway with reference to known signal components of Manduca sexta, another lepidopteran insect. S. exigua infected with Metarhizium rileyi, an entomopathogenic fungus, activated phospholipase A2 (PLA2) and phenoloxidase (PO) enzymes along with marked increases of expression levels of genes encoding three specific antimicrobial peptides, cecropin, gallerimycin, and hemolin. Among ten Toll receptors encoded in the genome of S. exigua, seven Toll genes were associated with immune responses against fungal infection by M. rileyi through individual RNA interference (RNAi) screening. In addition, two Spätzles (ligands of Toll receptor) were required for Toll signaling against the fungal infection. All predicted upstream components of the Toll pathway were inducible by the fungal infection. Individual RNAi screening showed that three PRRs (ßGRP-1, ßGRP-2, and GNBP3) and five SPs (ModSP, HP21, HP5, HP6, and HP8) were required for immune responses of S. exigua mediated by Toll signal pathway against the fungal infection. However, two PO-activating proteases (PAP1 and PAP3) were not required for PLA2 activation, although they were required for PO activation. These results suggest that PRRs and SPs conserved as upstream components in Toll signal pathway play crucial roles in triggering eicosanoid biosynthesis of S. exigua to mediate various immune responses against fungal infection.

ABCC2 is a functional receptor of Bacillus thuringiensis Cry1Ca in Spodoptera litura.

Spodoptera litura is a serious polyphagous pest in the whole world, which has developed resistance to most conventional insecticides and even some Bacillus thuringiensis (Bt) toxins. Cry1Ca has excellent insecticide activity against S. litura with potential application to control S. litura and delay the development of insect resistance. However, the mode of action of Cry1Ca in S. litura is poorly understood. Here, Cry1Ca-binding proteins were identified from S. litura by using pull down assays and liquid chromatography-tandem mass spectrometry (LC-MS/MS). The results indicated that aminopeptidase-N (APN), ATP binding cassette subfamily C member 2 (ABCC2), polycalin, actin and V-type proton ATPase subunit A may bind with Cry1Ca. Further study confirmed that ABCC2 fragment expressed in vitro can bind to Cry1Ca as demonstrated by Ligand blot and homologous competition experiments. The over-expression of endogenous SlABCC2 in Sf9 cells increased Cry1Ca cytotoxicity. Correspondingly, the vivo loss of function analyses by SlABCC2 small interfering RNAs (siRNAs) in S. litura larvae decreased the toxicity of Cry1Ca to larvae. Altogether, these results show that ABCC2 of S. litura is a functional receptor that is involved in the action mode of Cry1Ca.

Dry and Rainy Seasons Significantly Alter the Gut Microbiome Composition and Reveal a Key Enterococcus sp. (Lactobacillales: Enterococcaceae) Core Component in Spodoptera frugiperda (Lepidoptera: Noctuidae) Corn Strain From Northwestern Colombia.

Spodoptera frugiperda is a polyphagous pest of several crops of economic importance. Nowadays, the insect is broadly distributed in America and, recently, in Africa, Asia, and Australia. The species has diverged into corn and rice strains. The role of the gut microbiota in insect physiology is relevant due to its participation in crucial functions. However, knowledge of seasonal variations that alter the gut microbiome in pests is limited. Gut microbiome composition between the dry and rainy seasons was analyzed with cultured and uncultured approaches in S. frugiperda corn strain larvae collected at Northwest Colombia, as seasonal microbiome changes might fluctuate due to environmental changes. On the basis of culture-dependent methods, results show well-defined microbiota with bacterial isolates belonging to Enterococcus, Klebsiella (Enterobacteriales: Enterobacteriaceae), Enterobacter (Enterobacterales: Enterobacteriaceae), and Bacillus (Bacillales: Bacillaceae) genera. The community composition displayed a low bacterial diversity across all samples. The core community detected with uncultured methods was composed of Enterococcus, Erysipelatoclostridium (Erysipelotrichales: Erysipelotrichaceae), Rasltonia (Burkholderiales: Burkholderiaceae), and Rhizobium (Hyphomicrobiales: Rhizobiaceae) genera, and Enterobacteriaceae family members. Significant differences in microbiome diversity were observed between the two seasons. The relative abundance of Erysipelatoclostridium was high in the dry season, while in the phylotype ZOR0006 (Erysipelotrichales: Erysipelotrichaceae) and Tyzzerella (Lachnospirales: Lachnospiraceae) genus, the relative abundance was high in the rainy season. The overall low gut bacterial diversity observed in the S. frugiperda corn strain suggests a strong presence of antagonist activity as a selection factor possibly arising from the host, the dominant bacterial types, or the material ingested. Targeting the stability and predominance of this core microbiome could be an additional alternative to pest control strategies, particularly in this moth.

Comparison of Gut Bacterial Communities of Fall Armyworm (Spodoptera frugiperda) Reared on Different Host Plants.

Spodoptera frugiperda is a highly polyphagous and invasive agricultural pest that can harm more than 300 plants and cause huge economic losses to crops. Symbiotic bacteria play an important role in the host biology and ecology of herbivores, and have a wide range of effects on host growth and adaptation. In this study, high-throughput sequencing technology was used to investigate the effects of different hosts (corn, wild oat, oilseed rape, pepper, and artificial diet) on gut microbial community structure and diversity. Corn is one of the most favored plants of S. frugiperda. We compared the gut microbiota on corn with and without a seed coating agent. The results showed that Firmicutes and Bacteroidetes dominated the gut microbial community. The microbial abundance on oilseed rape was the highest, the microbial diversity on wild oat was the lowest, and the microbial diversity on corn without a seed coating agent was significantly higher than that with such an agent. PCoA analysis showed that there were significant differences in the gut microbial community among different hosts. PICRUSt analysis showed that most of the functional prediction categories were related to metabolic and cellular processes. The results showed that the gut microbial community of S. frugiperda was affected not only by the host species, but also by different host treatments, which played an important role in host adaptation. It is important to deepen our understanding of the symbiotic relationships between invasive organisms and microorganisms. The study of the adaptability of host insects contributes to the development of more effective and environmentally friendly pest management strategies.

Aspergillus flavus induced oxidative stress and immunosuppressive activity in Spodoptera litura as well as safety for mammals.

BACKGROUND: In the last few decades, considerable attention has been paid to entomopathogenic fungi as biocontrol agents, however little is known about their mode of action and safety. This study aimed to investigate the toxicity of Aspergillus flavus in insect Spodoptera litura by analyzing the effect of fungal extract on antioxidant and cellular immune defense. In antioxidant defense, the lipid peroxidation (Malondialdehyde content) and antioxidant enzymes activities (Catalase, Ascorbate peroxidase, Superoxide dismutase) were examined. In cellular immune defense, effect of A. flavus extract was analyzed on haemocytes using Scanning Electron Microscopy (SEM). Furthermore, mammalian toxicity was analyzed with respect to DNA damage induced in treated rat relative to control by comet assay using different tissues of rat (blood, liver, and kidney). RESULTS: Ethyl acetate extract of A. flavus was administrated to the larvae of S.litura using artificial diet method having concentration 1340.84 µg/ml (LC50 of fungus). The effect was observed using haemolymph of insect larvae for different time intervals (24, 48, 72 and 96). In particular, Malondialdehyde content and antioxidant enzymes activities were found to be significantly (p ≤ 0.05) increased in treated larvae as compared to control. A. flavus ethyl acetate extract also exhibit negative impact on haemocytes having major role in cellular immune defense. Various deformities were observed in different haemocytes like cytoplasmic leakage and surface abnormalities etc. Genotoxicity on rat was assessed using different tissues of rat (blood, liver, and kidney) by comet assay. Non-significant effect of A. flavus extract was found in all the tissues (blood, liver, and kidney). CONCLUSIONS: Overall the study provides important information regarding the oxidative stress causing potential and immunosuppressant nature of A. flavus against S. litura and its non toxicity to mammals (rat), mammals (rat), suggesting it an environment friendly pest management agent.

Compatibility of Bt biopesticides and adjuvants for Spodoptera frugiperda control.

Spodoptera frugiperda is a pest of economic importance for several crops with resistance reports to Bt crops and pesticides. Eco-friendly Bt biopesticides may be an alternative to chemical insecticides due to their selectivity and specificity. However, the efficacy of Bt biopesticides may be influenced by the association with other chemicals, such as adjuvants. This study evaluated the compatibility and toxicity of Bt biopesticides mixed with adjuvants for the control of S. frugiperda. The treatments included the association of Dipel SC and Dipel PM with adjuvants. Compatibility tests were used to evaluate the Bt mixture. Bt suspensions obtained from mixtures of Bt and adjuvants at 106 and 3 × 108 spores/mL-1 were used to evaluate S. frugiperda mortality and distilled water was used as the control. The addition of the adjuvant LI increased growth and sporulation, indicating compatibility with Bt biopesticides. The other adjuvants were toxic to reducing Bt growth and sporulation. Only the mixture of Bt with LI and Bt alone was effective to S. frugiperda. The addition of adjuvants to Bt biopesticide affect the Bt sporulation, growth and mortality.

The prostanoids, thromboxanes, mediate hemocytic immunity to bacterial infection in the lepidopteran Spodoptera exigua.

We report on a new insect prostanoid in a lepidopteran insect, Spodoptera exigua. Thromboxane B2 (TXB2) was detected by LC-MS/MS in extracts of larval epidermis, midgut, fat body and hemocytes, with highest amounts in hemocytes (about 300 ng/g tissue with substantial variation). Thromboxane A2 (TXA2) is an unstable intermediate that is non-enzymatically hydrolyzed into the stable TXB2. In S. exigua, both thromboxanes mediate at least two cellular immune responses to bacterial infection, hemocyte-spreading behavior and nodule formation. At the molecular level, a TXA2 synthase (SeTXAS) was identified from a group of 139 S. exigua cytochrome P450 monooxygenases. SeTXAS was highly similar to mammalian TXAS genes and is expressed in all developmental stages and four tested larval tissues. Immune challenge significantly enhanced SeTXAS expression, especially in hemocytes. RNA interference (RNAi) injections using gene-specific double stranded RNA led to reduced SeTXAS expression and suppressed the cellular immune responses, which were rescued following TXA2 or TXB2 injections. Unlike other PGs, TXA2 or TXB2 did not influence oocyte development in adult females. We infer that thromboxanes are present in insect tissues, where they mediate innate immune responses.

Effects of maize (Zea mays) genotypes and microbial sources in shaping fall armyworm (Spodoptera frugiperda) gut bacterial communities.

Plants can have fundamental roles in shaping bacterial communities associated with insect herbivores. For larval lepidopterans (caterpillars), diet has been shown to be a driving force shaping gut microbial communities, where the gut microbiome of insects feeding on different plant species and genotypes can vary in composition and diversity. In this study, we aimed to better understand the roles of plant genotypes, sources of microbiota, and the host gut environment in structuring bacterial communities. We used multiple maize genotypes and fall armyworm (Spodoptera frugiperda) larvae as models to parse these drivers. We performed a series of experiments using axenic larvae that received a mixed microbial community prepared from frass from larvae that consumed field-grown maize. The new larval recipients were then provided different maize genotypes that were gamma-irradiated to minimize bacteria coming from the plant during feeding. For field-collected maize, there were no differences in community structure, but we did observe differences in gut community membership. In the controlled experiment, the microbial inoculation source, plant genotype, and their interactions impacted the membership and structure of gut bacterial communities. Compared to axenic larvae, fall armyworm larvae that received frass inoculum experienced reduced growth. Our results document the role of microbial sources and plant genotypes in contributing to variation in gut bacterial communities in herbivorous larvae. While more research is needed to shed light on the mechanisms driving this variation, these results provide a method for incorporating greater gut bacterial community complexity into laboratory-reared larvae.