Corn Strain Research Articles

Adaptive evolution of invasive fall armyworms to maize with potential involvement of Cytochrome P450 genes

BackgroundAn invasion occurs when introduced species establish and maintain stable populations in areas outside of their native habitat. Adaptive evolution has been proposed to contribute to this process. The fall armyworm (Spodoptera frugiperda) is one of the major pest insects infesting maize in both invaded and native areas. The invasion of this species was reported from West Africa in 2016, followed by spreading across the Old World. We tested adaptive evolution to maize using 56 native samples from the USA and 59 invasive samples from Senegal, based on genomic and transcriptomic analyses.ResultsPrincipal component analysis revealed that the Senegalese population originated from corn strain. Three genetic loci were identified as targets of selective sweeps in the Senegalese population. These loci include four Cytochrome P450 genes (CYP321B1, CYP321B3, CYP321B4, and CYP337B5), as well as 12 genes of which the function is unclear. Transcriptomic analysis showed an overexpression of CYP321B1 and CYP321B3 genes in sfC samples compared to sfR samples. Additionally, these two genes were overexpressed when corn strain samples were exposed to maize. In larval feeding assays, the Senegalese population exhibited higher survival rates than a Floridan population across all four tested maize varieties.ConclusionsThese results suggest that the analyzed Senegalese population experienced adaptive evolution involving loci containing CYP genes, potentially associated with an increase in the survival rates on maize. We argue that the invasive success of the fall armyworm is contributed by stabilizing selection to maize.

Fall Armyworm Spodoptera frugiperda J.E. Smith (Lepidoptera: Noctuidae) in East Nusa Tenggara Province of Indonesia: Genetic Characterization and Strain Detection

<em>Spodoptera frugiperda</em> J.E. Smith (Lepidoptera: Noctuidae) is an invasive pest of corn plants spreading throughout the world, including East Nusa Tenggara (NTT), Indonesia. Despite the wide distribution, there is a lack of information on the strain or genetic diversity of the pest in NTT. Therefore, this study aimed to determine the strain of <em>S. frugiperda</em> from several areas in NTT with a molecular method using <em>cytochrome oxidase subunit 1</em> (<em>COI</em>)<em> </em>and <em>triose phosphate isomerase</em> (<em>Tpi</em>)<em> </em>gene markers. The<em> </em>samples were collected from 3 islands: Timor, Flores, and Sumba. Amplification of the marker genes was carried out using 3 specific primers to identify the strain obtained from samples. Subsequently, polymerase chain reaction (PCR) products were sequenced and the DNA sequences were analyzed using the BioEdit and BLAST programs. Phylogeny analyses were carried out using the MEGA 11 program to verify the strain group of samples with reference isolates from other countries found in GenBank. The PCR results showed product amplicon size 811 bp for the <em>CO1A</em> marker. Based on phylogeny tree analysis using <em>COI </em>marker, <em>S. frugiperda </em>from NTT showed 2 clades, namely corn and rice strains. The characterization results showed that <em>S. frugiperda</em> in NTT comprised 63.6% corn and 36.4% rice strains. <em>COIB </em>classified <em>S. frugiperda</em> from NTT into the h4 haplotype subgroup, while <em>Tpi </em>gene marker was in the corn strain. This study provided valuable information regarding the strain of <em>S. frugiperda</em> in Indonesia to determine the appropriate control strategy.

Dominant strain shift in the invasive fall armyworm (Lepidoptera: Noctuidae) populations in Thailand as inferred from mitochondrial COI and nuclear Tpi genes.

The fall armyworm, Spodoptera frugiperda (J. E. Smith, 1797) (Lepidoptera: Noctuidae), is a significant global pest, that exhibits 2 discernible strains, corn strain (CS) and rice strain (RS). After initial detection in the eastern hemisphere in 2016, the dominant strain was identified as RS based only on cytochrome C oxidase subunit I (COI) mitochondrial gene from limited samples from various countries, including Thailand. This study aimed to assess strain and haplotype variation in the S. frugiperda populations in Thailand using both mitochondrial COI and nuclear triosephosphate isomerase (Tpi) genes. Analyses of COI sequences (n = 105) revealed 2 predominant haplotypes, COICSh4 (82.86%) and COIRSh1 (17.14%), and the analyses of Tpi sequences (n = 99) revealed 6 haplotypes, with TpiCa1a (53.53%) being the most prevalent. Of the 98 caterpillar samples, the majority exhibited true CS (83.67%) for both genes. Meanwhile, interstrain hybrids, indicated by gene discordance, accounted for the minority (16.33%). Interestingly, despite the initial dominance of RS during the 2018 outbreak, the current study identified CS as the prevalent strain across all localities in Thailand. These findings suggested a shift in S. frugiperda dynamics in Thailand that was possibly influenced by factors, such as competitive exclusion principle, pesticide usage in rice cultivation, and preferences for corn over rice. Our study suggests a need to reexamine the previous reports of rice-strain dominance in various countries in the eastern hemisphere after the initial invasion.

Impact of Maize Nutrient Composition on the Developmental Defects of Spodoptera frugiperda

Spodoptera frugiperda (J.E. Smith) is a crucial agricultural pest owing to its global impact on >300 crops. Among these, the corn strain of S. frugiperda causes significant damage to maize (Zea mays L.). However, limited research exists on the influence of maize nutrients on the metamorphosis of S. frugiperda and the underlying mechanisms. In this study, the effects of different growth stages of maize leaves, namely, tender leaves (tender) and mature leaves (mature), on various aspects of larval development, including body weight, body length, developmental age, pupation rate, and eclosion rate, were investigated. Additionally, we measured the levels of 20-hydroxyecdysone (20E) and three types of juvenile hormone (JH; i.e., JH I–III) in S. frugiperda larvae fed on tender or mature. The results revealed that larvae fed on Tender exhibited significantly prolonged instar duration, reduced body weight and length, and decreased pupation and eclosion rates, with the emergence of abnormal adults. Analysis of nutritional components in maize leaves revealed significantly higher levels of amino acids, soluble sugars, and sterols in mature than in tender. Hormone analysis in S. frugiperda larvae revealed higher 20E titers in individuals feeding on mature during prepupal and pupal stages. We demonstrated the crucial role of sterols in regulating the level of 20E and pupation rate of S. frugiperda. Based on these findings, we propose that isoleucine, arginine, glutamic acid, sucrose, campesterol, and β-sitosterol serve as key nutrients influencing the development of S. frugiperda. Moreover, β-sitosterol is a significant factor influencing the interaction between maize leaves and S. frugiperda. Our research results provide a reference for the control strategy of S. frugiperda based on breeding insect-resistant varieties by altering host nutrition.

New occurrence of corn and rice strains of Spodoptera frugiperda (Lepidoptera: Noctuidae) in Bali and Lesser Sunda: Genetic diversity, distribution, and damage

Abstract. Yudha IKW, Supartha IW, Susila IW, Sudiarta P, Wijaya IN, Wiradana PA. 2024. New occurrence of corn and rice strains of Spodoptera frugiperda (Lepidoptera: Noctuidae) in Bali and Lesser Sunda (Indonesia): Genetic diversity, distribution, and damage. Biodiversitas 25: 1890-1900. Spodoptera frugiperda is an invasive pest with rapid proliferation and is responsible for reducing corn productivity in several regions in Indonesia, including Bali and Lesser Sunda in Indonesia. Therefore, this study aimed to determine the geographic distribution, genetic diversity, and specific genes of S. frugiperda as well as assess its attacks in Bali and Lesser Sunda (NTB and NTT) regions. The study procedures were carried out using field surveys, followed by molecular identification to determine the genetic diversity of S. frugiperda with the COI locus. A total of 150 infected corn plants were sampled using the diagonal sampling method, with a unit size of 5 m × 5 m. The distribution data obtained were then analyzed using the QGIS application and SPSS 22 for statistical analysis. The geographic distribution results showed that S. frugiperda was evenly distributed in the provinces of Bali and Lesser Sunda, with the observation of 2 strains, namely corn and rice. Corn strain was more specifically found in the Karangasem, Flores, Lombok Highlands, and Timor areas, while rice strain occured in the Jembrana, Sumbawa, Sumba, Flores, and Lombok lowland areas. In addition, a total of 12 specific nucleotide bases from S. frugiperda gene were found in Bali, NTB, and NTT regions. The findings also showed that the haplotype network of Bali, NTB, and NTT populations was effectively isolated from other locations and was in the process of genetic divergence. The 3-year invasion of S. frugiperda in Indonesian territory was reported to have experienced a process of genetic population development. Lombok Island had the highest average plant damage at 54.63%, which was not significantly different from the value of Sumbawa, Bali, and Sumba at 47.79%, 42.65%, and 40.72%, respectively. On the other hand, the lowest plant damage level in Timor at 20.95%, followed by Flores (at 30.38%).

Divergent Aspergillus flavus corn population is composed of prolific conidium producers: Implications for saprophytic disease cycle

ABSTRACT The ascomycete fungus Aspergillus flavus infects and contaminates corn, peanuts, cottonseed, and tree nuts with toxic and carcinogenic aflatoxins. Subdivision between soil and host plant populations suggests that certain A. flavus strains are specialized to infect peanut, cotton, and corn despite having a broad host range. In this study, the ability of strains isolated from corn and/or soil in 11 Louisiana fields to produce conidia (field inoculum and male gamete) and sclerotia (resting bodies and female gamete) was assessed and compared with genotypic single-nucleotide polymorphism (SNP) differences between whole genomes. Corn strains produced upward of 47× more conidia than strains restricted to soil. Conversely, corn strains produced as much as 3000× fewer sclerotia than soil strains. Aspergillus flavus strains, typified by sclerotium diameter (small S-strains, <400 μm; large L-strains, >400 μm), belonged to separate clades. Several strains produced a mixture (M) of S and L sclerotia, and an intermediate number of conidia and sclerotia, compared with typical S-strains (minimal conidia, copious sclerotia) and L-strains (copious conidia, minimal sclerotia). They also belonged to a unique phylogenetic mixed (M) clade. Migration from soil to corn positively correlated with conidium production and negatively correlated with sclerotium production. Genetic differences correlated with differences in conidium and sclerotium production. Opposite skews in female (sclerotia) or male (conidia) gametic production by soil or corn strains, respectively, resulted in reduced effective breeding population sizes when comparing male:female gamete ratio with mating type distribution. Combining both soil and corn populations increased the effective breeding population, presumably due to contribution of male gametes from corn, which fertilize sclerotia on the soil surface. Incongruencies between aflatoxin clusters, strain morphotype designation, and whole genome phylogenies suggest a history of sexual reproduction within this Louisiana population, demonstrating the importance of conidium production, as infectious propagules and as fertilizers of the A. flavus soil population.

Comparative analysis of Spodoptera frugiperda (J. E. Smith) (Lepidoptera, Noctuidae) corn and rice strains microbiota revealed minor changes across life cycle and strain endosymbiont association.

Spodoptera frugiperda (FAW) is a pest that poses a significant threat to corn production worldwide, causing millions of dollars in losses. The species has evolved into two strains (corn and rice) that differ in their genetics, reproductive isolation, and resistance to insecticides and Bacillus thuringiensis endotoxins. The microbiota plays an important role in insects' physiology, nutrient acquisition, and response to chemical and biological controls. Several studies have been carried out on FAW microbiota from larvae guts using laboratory or field samples and a couple of studies have analyzed the corn strain microbiota across its life cycle. This investigation reveals the first comparison between corn strain (CS) and rice strain (RS) of FAW during different developmental insect stages and, more importantly, endosymbiont detection in both strains, highlighting the importance of studying both FAW populations and samples from different stages. The composition of microbiota during the life cycle of the FAW corn and rice strains was analyzed through high-throughput sequencing of the bacterial 16S rRNA gene using the MiSeq system. Additionally, culture-dependent techniques were used to isolate gut bacteria and the Transcribed Internal Spacer-ITS, 16S rRNA, and gyrB genes were examined to enhance bacterial identification. Richness, diversity, and bacterial composition changed significantly across the life cycle of FAW. Most diversity was observed in eggs and males. Differences in gut microbiota diversity between CS and RS were minor. However, Leuconostoc, A2, Klebsiella, Lachnoclostridium, Spiroplasma, and Mucispirilum were mainly associated with RS and Colidextribacter, Pelomonas, Weissella, and Arsenophonus to CS, suggesting that FAW strains differ in several genera according to the host plant. Firmicutes and Proteobacteria were the dominant phyla during FAW metamorphosis. Illeobacterium, Ralstonia, and Burkholderia exhibited similar abundancies in both strains. Enterococcus was identified as a conserved taxon across the entire FAW life cycle. Microbiota core communities mainly consisted of Enterococcus and Illeobacterium. A positive correlation was found between Spiroplasma with RS (sampled from eggs, larvae, pupae, and adults) and Arsenophonus (sampled from eggs, larvae, and adults) with CS. Enterococcus mundtii was predominant in all developmental stages. Previous studies have suggested its importance in FAW response to B. thuringensis. Our results are relevant for the characterization of FAW corn and rice strains microbiota to develop new strategies for their control. Detection of Arsenophonus in CS and Spiroplasma in RS are promising for the improvement of this pest management, as these bacteria induce male killing and larvae fitness reduction in other Lepidoptera species.

Identification and Genetic Diversity of Spodoptera frugiperda J. E. Smith (Lepidoptera: Noctuidae) in Egypt

Fall armyworm, Spodoptera frugiperda, is a serious agricultural pest native to tropical and subtropical regions of the Western Hemisphere and has invaded Africa and further spread into most countries of Asia within two years. In Egypt, researchers have conducted thorough investigations into the behavior of the fall armyworm and various methods to manage its impact. This study aims to further our understanding of the genetic diversity of fall armyworm populations in Egypt. By collecting specimens from five provinces across the country, we sought to analyze their genetic makeup. Through examination of partial sequences of the mitochondrial cytochrome oxidase subunit I (COI), we identified three distinct haplotypes. Phylogenetic analysis suggests that the primary sources of Spodoptera frugiperda in Egypt likely stem from both Asian and African origins. Employing the PCR-RFLP technique on the complete COI sequence, we were able to discern genotype patterns within the fall armyworm population. Our findings indicate the presence of two distinct strains—the Corn and Rice strains—within Egypt. This research contributes essential insights into the genetic diversity of insects in Egypt, providing valuable knowledge that can inform more effective strategies for managing this agricultural pest.

Invasive fall armyworms are corn strain

The fall armyworm (Spodoptera frugiperda) is one of the major pest insects in diverse crop plants, including maize, rice, and cotton. While the fall armyworm is native to North and South America, its invasion was first reported in West Africa in 2016. Since then, this species has rapidly spread across Sub-Saharan Africa, Asia, and Oceania, as well as Egypt and Cyprus. The fall armyworm is composed of two sympatric strains, the corn and rice strains, designated to their preferred host plants, in native areas. It remains surprisingly unclear whether invasive fall armyworms belong to the corn strain, rice strain, or hybrids of the two, despite a large number of population genetics studies. In this study, we performed population genomics analyses using globally collected 116 samples to identify the strains of invasive fall armyworms. We observed that invasive fall armyworms are genomically most similar to the corn strain. The reconstructed phylogenetic tree supports the hypothesis that invasive fall armyworms originated from the corn strain. All genomic loci of invasive populations exhibit higher genetic similarity to the corn strains compared to the rice strains. Furthermore, we found no evidence of gene flow from rice strains to invasive populations at any genomic locus. These results demonstrate that invasive fall armyworms belong to the corn strain. These results suggest that invasive fall armyworms likely have very limited potential to infest rice. Therefore, the management plan should primarily focus on crops preferred by the corn strain.

Two host-plant strains in the fall armyworm.

The fall armyworm (Spodoptera frugiperda) is one of the major pest insects damaging diverse crops including cotton, corn, rice, and sorghum. Fall armyworms have been identified as two morphologically indistinguishable strains, the corn strain, and the rice strain, named after their preferred host-plants. Although initially recognized as host-plant strains, there has been an ongoing debate regarding whether the corn and rice strains should be considered as such. In this article, we present arguments based on recent population genomics studies supporting that these two strains should be considered to be host-plant strains. Furthermore, host-plant adaptation appears to be a driving evolutionary force responsible for incipient speciation in the fall armyworm.

Genetic variation in the triosephosphate isomerase gene of the fall armyworm and its distribution across China.

The fall armyworm (FAW), Spodoptera frugiperda, has colonized and caused consistent damage in the Eastern hemisphere. The identification of various FAW strains is essential for developing precise prevention and control measures. The triosephosphate isomerase (Tpi) gene is recognized as an effective marker closely linked to FAW subpopulations. However, most current studies primarily focus on the comparison of variations in specific gene sites of this gene. In this study, we conducted full-length sequencing of the Tpi genes from 5 representative FAW groups. Our findings revealed that the Tpi genes varied in length from 1220 to 1420bp, with the primary variation occurring within 4 introns. Notably, the exon lengths remained consistent, at 747bp, with 37 observed base variations; however, no amino acid variations were detected. Through sequence alignment, we identified 8 stable variation sites that can be used to distinguish FAW strains in the Eastern hemisphere. Additionally, we performed strain identification on 1569 FAW samples collected from 19 provinces in China between 2020 and 2021. The extensive analysis indicated the absence of the rice strain in the samples. Instead, we only detected the presence of the corn strain and the Zambia strain, with the Zambia strain being distributed in a very low proportion (3.44%). Furthermore, the corn strain could be further categorized into 2 subgroups. This comprehensive study provides a valuable reference for enhancing our understanding of FAW population differentiation and for improving monitoring and early warning efforts.

Molecular Characterization Analysis and Adaptive Responses of Spodoptera frugiperda (Lepidoptera: Noctuidae) to Nutritional and Enzymatic Variabilities in Various Maize Cultivars.

The fall armyworm, Spodoptera frugiperda Smith (Lepidoptera: Noctuidae), a common agricultural pest known for its extensive migration and wide host ranges, causes considerable harm to maize (Zea mays L.). In this study, we utilized two molecular marker genes, COI and Tpi, to compare the genetic characteristics of the collected original samples. Additionally, through an interactive study between S. frugiperda larvae and six maize varieties aiming to understand the insect's adaptability and resistance mechanisms, our analysis revealed that both the COI and Tpi genes identified S. frugiperda as the corn strain. Further examination of the larvae showed significant differences in nutritional indices, digestive, and detoxification enzyme activities. Special maize varieties were found to offer higher efficiency in nutrient conversion and assimilation compared with common varieties. This study revealed adaptations in S. frugiperda's digestive and detoxification processes in response to the different maize varieties. For instance, larvae reared on common maize exhibited elevated amylase and lipase activities. Interestingly, detoxification enzyme activities exhibited different patterns of variation in different maize varieties. The Pearson correlation analysis between nutritional indices, enzyme activities, and the nutritional content and secondary metabolites of maize leaves provided deeper insights into the pest's adaptability. The results highlighted significant relationships between specific nutritional components in maize and the physiological responses of S. frugiperda. Overall, our findings contribute substantially to the understanding of S. frugiperda's host plant adaptability, offering critical insights for the development of sustainable pest management strategies.

Pheromonal variation and mating between two mitotypes of fall armyworm (Spodoptera frugiperda) in Africa

In the Americas, the fall armyworm (Spodoptera frugiperda) exists in two genetically distinct strains, the corn (C) and rice (R) strains. Despite their names, these strains are not associated with host plant preferences but have been shown to vary in pheromone composition and male responses. Recently, S. frugiperda was detected in Africa as an invasive species, but knowledge about variation in strain types, pheromone composition and inter-strain mating of populations of the pest in the continent has not been fully examined. Therefore, this study aimed to investigate variations, if any in the pheromone composition of female moths, male moth responses, and mating between C and R mitotypes of S. frugiperda populations in Kenya, as well as their geographic distribution. Strains (mitotypes) of S. frugiperda were identified using mitochondrial DNA (mtDNA) markers, and their pheromonal composition determined by coupled gas chromatography–mass spectrometric (GC–MS) analysis. Male moth responses to these compounds were evaluated using GC-electroantennographic detection (EAD), electroantennogram (EAG), and wind tunnel assays. Oviposition assays were used to determine whether R and C mitotype moths could mate and produce eggs. The results showed that both the R and C mitotypes were present, and there were no statistically significant differences in their distribution across all sampled locations. Five pheromone compounds including (Z)-7-dodecenyl acetate (Z7-12:OAc), (Z)-7-tetradecenyl acetate (Z7-14:OAc), (Z)-9-tetradecenyl acetate (Z9-14:OAc), (Z)-11-tetradecenyl acetate (Z11-14:OAc) and (Z)-11-hexadecenyl acetate (Z11-16:OAc), were detected in the pheromone glands of female moths of both mitotypes, with Z9-14:OAc being the most abundant. The relative percentage composition of Z9-14:OAc was similar in both mitotypes. However, the R mitotype had a 2.7 times higher relative percentage composition of Z7-12:OAc compared to the C mitotype moth, while the C mitotype moth had a 2.4 times higher relative percentage composition of Z11-16:OAc than the R mitotype moth. Male moths of both mitotypes exhibited similar responses to the pheromone compounds, showing the strongest responses to Z9-14:OAc and Z7-12:OAc in electrophysiological and behavioural assays. There was mating between R and C mitotypes with egg production comparable to mating within the same mitotype. Our results revealed that differences between the two S. frugiperda mitotypes are characterized by female moth pheromone composition rather than male moth responses to the pheromones, and that this does not prevent hybridisation between the mitotypes, which may have implications for their management.

Heterosis effect for larval performance of fall armyworm interstrain hybrids.

Spodoptera frugiperda, also known as fall armyworm (FAW), is an invasive crop pest that can feed on a variety of host plants, posing a serious threat to food security. There are two sympatric strains of FAW that are morphologically identical but described with different food preferences: the "rice strain" (SfR) and the "corn strain" (SfC). A few genetic loci exist to identify these two strains. Mitochondrial and Z-chromosome-linked haplotypes are the most used, but the biggest part of the genome displays little polymorphism between strains that could explain their adaptation to different plants. We have previously observed consistent transcription differences between the strains in both laboratory and natural populations. Therefore, we wonder if there are effects from host-strain-associated loci, maternally or paternally inherited, on FAW performance that could explain the divergence between the two FAW strains. To test this hypothesis, we first produced two F1 hybrid generations (SfR ♀ × SfC ♂, SfC ♀ × SfR ♂). These reciprocal hybrids should be heterozygous for all chromosomes except for the maternally inherited mitochondrial and sexual W chromosomes. To evaluate whether plant preference is determined by these genetic loci, we cultivated the two hybrids and the two parental strains in triplicate on an artificial diet and recorded several phenotypic traits such as weight over time, survival rate, emerging rate, developmental time, and sex ratio. Then, the same performance experiment was carried out on corn plants. Surprisingly, on the artificial diet, the two hybrid genotypes were both more performant than the two parental strains in terms of survival rate, pupal emerging rate, and developmental time, whereas they were intermediate to the inbred parental strains in pupal weight. On the corn plant diet, both hybrid genotypes outperformed the two parental strains in larval weight. Although these asymmetrical results revealed that mitochondrial or sex-linked haplotypes alone cannot explain the performance differences, they suggested a heterosis effect in FAW. A reduction of the female number for the CR genotype and the decreased F1 offspring reproduction in both hybrids suggested the possibility of Haldane's rule, which might be explained by the dominance model.

Mechanism of the Change in the Intestinal Microbiota of C-Strain Spodoptera frugiperda (Lepidoptera: Noctuidae) after an Interspecific Transference between Rice and Corn.

Spodoptera frugiperda (J.E.Smith) (Lepidoptera: Noctuidae) was first found in 2019 in Yunnan, China, and it was characterized as a corn strain; it was also found on rice strains there, and it damages rice in China, but little is known about the effect of host plant transfer on the intestinal microbiota and the activities of detoxification enzymes in the C-strain (corn strain) S. frugiperda. The intestinal microbiota and the protective enzyme activity of S. frugiperda that were transferred from rice plants were assessed, and the fourth generation of insects transferred from corn were studied; the gene types of S. frugiperda that were transferred from rice plants were tested using mitochondrial Tpi gene sequences. The results showed that the intestinal microbiota in the C-strain S. frugiperda were changed after the host transference, and the diversity and richness of the intestinal bacterial communities of the S. frugiperda feeding on rice were significantly reduced after the transfer of the host from corn. The predominant species of intestinal bacteria of the S. frugiperda on rice transferred from corn were Enterococcus and Enterobacter, with relative abundances of 28.7% and 66.68%; the predominant species of intestinal bacteria of the S. frugiperda that were transferred from rice and feeding on corn were Enterococcus (22.35%) and Erysipelatoclostridium (73.92%); and the predominant species of intestinal bacteria of S. frugiperda feeding on corn was Enterococcus, with a relative abundance of 61.26%. The CAT (catalase) activity of the S. frugiperda transferred from corn onto rice from corn was reduced, the POD (peroxidase) activity was significantly increased after the transfer from corn, and no significant variations were found for the SOD (superoxide dismutase), CarE (carboxylesterase), and GST (glutathione S-transferase) activities of S. frugiperda after the host plant transfer. The results showed that after feeding on rice, the activities of CAT and POD in the in S. frugiperda body changed in order to resist plant secondary metabolites from corn or rice, but there was no significant change in the detoxification enzymes in the body. In summary, switching the host plant between corn and rice induced variations in the intestinal microbiota in C-strain S. frugiperda owing to the strain difference between the C-strain and the R-strain (rice strain), and this was consistent with the results of the activities of detoxification enzymes. The results indicat that changes in intestinal microbiota and physiological enzymes may be important reasons for the adaptive capacity of C-strain S. frugiperda to rice.

Microbiome analysis of Spodoptera frugiperda (Lepidoptera, Noctuidae) larvae exposed to Bacillus thuringiensis (Bt) endotoxins.

Spodoptera frugiperda (or fall armyworm, FAW) is a polyphagous pest native to Western Hemisphere and recently discovered in the Eastern Hemisphere. In Colombia, S. frugiperda is recognized as a pest of economic importance in corn. The species has genetically differentiated into two host populations named "corn" and "rice" strains. In 2012, a study made in central Colombia demonstrated that the corn strain is less susceptible to Bacillus thuringiensis (Bt) endotoxins (Cry1Ac and Cry 1Ab) than the rice strain. In this country, Bt transgenic corn has been extensively produced over the last 15 years. Since gut microbiota plays a role in the physiology and immunity of insects, and has been implicated in promoting the insecticidal activity of Bt, in this study an analysis of the interaction between Bt endotoxins and FAW gut microbiota was made. Also, the detection of endosymbionts was performed here, as they might have important implications in the biological control of a pest. The composition and diversity of microbiomes associated with larval specimens of S. frugiperda(corn strain) was investigated in a bioassay based on six treatments in the presence/absence of Bt toxins and antibiotics (Ab) through bacterial isolate analyses and by high throughput sequencing of the bacterial 16S rRNA gene. Additionally, species specific primers were used, to detect endosymbionts from gonads in S. frugiperda corn strain. Firmicutes, Proteobacteria and Bacteroidota were the most dominant bacterial phyla found in S. frugiperda corn strain. No significant differences in bacteria species diversity and richness among the six treatments were found. Two species of Enterococcus spp., E. mundtii and E. casseliflavus were detected in treatments with Bt and antibiotics, suggesting that they are less susceptible to both of them. Additionally, the endosymbiont Arsenophonus was also identified on treatments in presence of Bt and antibiotics. The results obtained here are important since little knowledge exists about the gut microbiota on this pest and its interaction with Bt endotoxins. Previous studies made in Lepidoptera suggest that alteration of gut microbiota can be used to improve the management of pest populations, demonstrating the relevance of the results obtained in this work.

Spodoptera frugiperda population structure and influence of farmers’ practices on gut biodiversity for sustainable management of the pest in Kenya

Fall armyworm (FAW), Spodoptera frugiperda, is a highly polyphagous pest that recently invaded Kenya, among other African countries. Information on the pest’s genetic diversity and mechanisms conferring insecticide resistance, in addition to farmers’ knowledge and perceptions on the applicable mitigation measures, inform the development of sustainable management strategies. Therefore, this study collected cross-sectional data from 800 farmers in Kenya and documented their knowledge and perceptions on FAW and factors influencing their choice of FAW control methods. Additionally, we identified the strains present in 8 counties in Kenya using the mitochondrial Cytochrome Oxidase sub-unit I (mt COI) gene, and correlated pesticide use to gut microbiome diversity via 16S rRNA metagenomics to investigate the probable contribution of gut bacteria towards insecticide resistance evolution. All farmers reported FAW infestations, and 24% reported limited and total non-response of FAW to insecticides. Fall armyworm rice-strain and corn-strain were detected ravaging corn fields. However, the corn-strain revealed higher microbial diversity than the rice-strain. Furthermore, pathogenic bacterial genera were elevated in the insect gut in both corn and rice strains after chemical-treatments. Insecticide–endosymbiont interactions should be further explored, and farmers’ training on effective alternative pest control methods is recommended.

Genetic variation of pest fall armyworm Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae) in different landscapes in Bogor

Spodoptera frugiperda is an invasive pest from the American continent that attacks corn (Zea mays) and rapidly invaded Africa and Asia. Two main factors that support migration and population distribution of this species are suitable habitats and human activities. To date, two genetic strains of S. frugiperda have been found in corn in Indonesia: the corn strain (CS) and the rice strain (RS). The most accurate gene markers to detect these strains are COI and Tpi, which are located in mitochondria and Z chromosome. This study aims to determine the existing strains of S. frugiperda and their distribution in various landscapes in Bogor Regency. The research was conducted from July 2020 to December 2021 in Bogor, West Java. Sampling of S. fungiperda was carried out from corn plants in Leuwisadeng, Pamijahan1, Pamijahan2, Kemang, Tenjolaya, Dramaga, Cigombong, Cijeruk, Tamansari, and Ciomas. Larval samples were collected and preserved using 96% ethanol, followed by DNA extraction, DNA amplification, electrophoresis, and DNA sequencing. Distribution data were analyzedusing QGIS and Google Earth Pro programs, and statistical analysis was performed using SPSS 22. Sequence data were edited using GeneStudio, aligned using ClustalW in BioEdit, and the phylogeny tree was reconstructed using the neighbor-joining method (bootstrap 1000x) using MEGA X. The obtained sequences were compared with sequences from the GenBank® database. The results showed the presence of two distinct strains of COI (COI-CSh4 and COI-RS) and one strain of Tpi (Tpi-C) in Bogor. The study found no relationship between thelandscape structure and genetic variation of S. frugiperda.

Identification of Spodoptera frugiperda (Lepidoptera: Noctuidae) and its two host strains in China by PCR-RFLP.

The fall armyworm (FAW) Spodoptera frugiperda was first found in China in 2018. In other countries, FAW has evolved corn and rice strain biotypes. It is not possible to identify these strains based on morphology. In addition, FAW is very similar in appearance to several other common pests. These situations bring great challenges to the population management of FAW. In this study, we developed a rapid identification method based on PCR-RFLP to distinguish the two FAW strains and the FAW from other lepidopteran pests. A 697 bp mitochondrial cytochrome c oxidase I (COI) was cloned and sequenced from FAW, Spodoptera litura, Spodoptera exigua, and Mythimna separata. The COI fragments of these species revealed unique digestion patterns created by three enzymes (Tail, AlWN I, and BstY II). Thus, these four species can be distinguished from each other. The enzyme Ban I recognized a unique SNP site on a 638 bp triosephosphate isomerase (Tpi) fragment of the corn strain FAW. The Tpi fragment of the corn strain was cut into two bands. However, the rice strain could not be digested. Using this method, all 28 FAW samples collected from different host plants and locations in China were identified as the corn strain. This suggests that the rice strain has not yet invaded China. This method allows discrimination of FAW from other Lepidopteran pests and distinguishes the two FAW host strains.

Population genomics of fall armyworm by genotyping-by-sequencing: Implications for pest management.

The fall armyworm (FAW), Spodoptera frugiperda, is a significant pest of many crops in the world and it is native to the Americas, where the species has shown the ability to rapidly evolve resistance to insecticides and transgenic plants. Despite the importance of this species, there is a gap in the knowledge regarding the genetic structure of FAW in South America. Here, we examined the genetic diversity of FAW populations across a wide agricultural area of Brazil and Argentina using a Genotyping-by-Sequencing (GBS) approach. We also characterized samples by their host strain based on mitochondrial and Z-linked genetic markers. The GBS methodology enabled us to discover 3309 SNPs, including neutral and outlier markers. Data showed significant genetic structure between Brazil and Argentina populations, and also among the Argentinian ecoregions. Populations inside Brazil showed little genetic differentiation indicating high gene flow among locations and confirming that structure is related to the presence of corn and rice strains. Outlier analysis indicated 456 loci putatively under selection, including genes possibly related to resistance evolution. This study provides clarification of the population genetic structure of FAW in South America and highlights the importance of genomic research to understand the risks of spread of resistance genes.