Spodoptera Frugiperda Multiple Nucleopolyhedrovirus Research Articles

Generation and characterization of a novel ovariole cell line derived from Spodoptera frugiperda in China with sensitivity to both SfMNPV and AcMNPV

Spodoptera frugiperda multiple nucleopolyhedrovirus (SfMNPV), belonging to the species Alphabaculovirus spofrugiperdae, has been recently registered as an insecticide in China. This virus has a specific effect on the global major agricultural pest Spodoptera frugiperda. To gain insights into viral infection, replication processes, and the complex formation of viral particles, in vitro studies using cell lines are essential tools. Although the IPLB-Sf9 and IPLB-Sf21 cell lines derived from S. frugiperda are widely used for studies on the infection and replication mechanisms of Autographa californica multiple nucleopolyhedrovirus (AcMNPV), their capacity to produce viral polyhedra after SfMNPV infection is not optimal. To address this limitation, a novel cell line named IOZCAS-Sf-1 has been developed from a S. frugiperda population sourced Yunnan, China. The mitochondrial COX1 gene analysis confirmed the species origin of the IOZCAS-Sf-1 cell line. Furthermore, a comparative study was carried out to contrast the COX1 gene sequence of this novel cell line with that of IPLB-Sf9, highlighting the distinctions between the two. Importantly, the IOZCAS-Sf-1 cells exhibited a remarkable ability to generate polyhedra when infected with AcMNPV and SfMNPV, respectively. Consequently, this cellular lineage is considered a promising and valuable resource. It serves not only to investigate the molecular mechanisms of viral replication and its impact on host cells, but also to explore the transfection efficiency of SfMNPV DNA. This exploration further expands into its potential application in recombinant DNA experiments, laying a theoretical groundwork for the advancement of more effective biopesticides and sustainable agricultural practices.

A qPCR Assay for the Quantification of Selected Genotypic Variants of Spodoptera frugiperda Multiple Nucleopolyhedrovirus (Baculoviridae).

Alphabaculoviruses are lethal dsDNA viruses of Lepidoptera that have high genetic diversity and are transmitted in aggregates within proteinaceous occlusion bodies. This mode of transmission has implications for their efficacy as biological insecticides. A Nicaraguan isolate of Spodoptera frugiperda multiple nucleopolyhedrovirus (SfMNPV-NIC) comprising nine genotypic variants has been the subject of considerable study due to the influence of variant interactions on the insecticidal properties of mixed-variant occlusion bodies. As part of a systematic study on the replication and transmission of variant mixtures, a tool for the accurate quantification of a selection of genotypic variants was developed based on the quantitative PCR technique (qPCR). First, primer pairs were designed around a region of high variability in four variants named SfNic-A, SfNic-B, SfNic-C and SfNic-E to produce amplicons of 103-150 bp. Then, using cloned purified amplicons as standards, amplification was demonstrated over a dynamic range of 108-101 copies of each target. The assay was efficient (mean ± SD: 98.5 ± 0.8%), reproducible, as shown by low inter- and intra-assay coefficients of variation (<5%), and specific to the target variants (99.7-100% specificity across variants). The quantification method was validated on mixtures of genotype-specific amplicons and demonstrated accurate quantification. Finally, mixtures of the four variants were quantified based on mixtures of budded virions and mixtures of DNA extracted from occlusion-derived virions. In both cases, mixed-variant preparations compared favorably to total viral genome numbers by quantification of the polyhedrin (polh) gene that is present in all variants. This technique should prove invaluable in elucidating the influence of variant diversity on the transmission and insecticidal characteristics of this pathogen.

Simplified and cool texturing diets for in vivo inoculation of Spodoptera frugiperda multiple nucleopolyhedrovirus (SfMNPV)

The inoculation of viral entomopathogens in vivo requires study of each pathosystem. Several factors interfere in the cost of production and consequently in the availability of virus-based formulations. For the Spodoptera frugiperda multiple nucleopolyhedrovirus (SfMNPV), employed in the management of the fall armyworm Spodoptera frugiperda, factors such as host cannibal habit, temperature, and artificial diet of viral inoculation are important to research. In this work we propose to evaluate a diet based on textured soy protein, without heating during preparation, for viral inoculation and an artificial diet of simplified composition, based on wheat germ, to complete the feeding of larvaes during the stage of viral inoculation in groups of insects. S. frugiperda larvae were inoculated with SfMNPV virus in two diets: an artificial diet similar to that of mass rearing of the host and texturized soy protein at the following temperatures and respective ages: at 25 °C at 6 and 8 days after hatching and 31 °C at 4 and 6 days after larvae hatching. And, subsequently, viral inoculation was evaluated in a group of 300 larvae under different incubation times and temperature conditions, complementing feeding at this stage with a diet of simplified composition. The results show that it is possible to inoculate viruses without loss of viral polyhedra production in a textured soy protein-based diet and supplement the larvae diet with an artificial diet of simplified composition to complete the viral infection stage in groups of infected insects.

The use of baculovirus Spodoptera SfMNPV alone and combined with herbicides and adjuvant to control Spodoptera frugiperda (Smith, 1797) (Lepidoptera: Noctuidae)

Four independent experiments were carried out to evaluate the use of Spodoptera frugiperda multiple nucleopolyhedrovirus (SfMNPV) alone and mixed in different combinations with herbicides (atrazine and tembotrione) and adjuvant (soybean oil) to control Spodoptera frugiperda in maize. Experiments evaluated S. frugiperda mortality (%) under controlled conditions (26 ± 2 °C, relative humidity of 70 % ± 10 %, and 14:10 h L:D photoperiod) after feeding using a treated artificial diet (experiment 1) and maize leaves (experiment 2), both immediately and four hours after spraying the studied treatments (experiment 3). An additional experiment evaluated plant damage caused by S. frugiperda in the field (visual observation) on various days after spraying the tested treatments (experiment 4). The addition of the herbicide atrazine did not reduce the efficiency of SfMNPV in S. frugiperda control in any of the experiments. Thus, SfMNPV could be used in a tank mix with this herbicide, which would be economically attractive to farmers, facilitating SfMNPV adoption in the field. In contrast to atrazine, the herbicide tembotrione and the adjuvant (soybean oil) had an antagonistic interaction with SfMNPV, but only when sprayed four hours after preparation. Thus, the combination of SfMNPV with tembotrione and soybean oil can also be used by farmers if sprayed immediately after mixing with the baculovirus.

Vegetable waste extracts as enhancers of baculovirus infections

Vegetable waste extracts (VWE) contain a great variety of antioxidants such as polyphenols, which have shown to potentiate baculovirus infections, making them ingredients for pest control ingredients. In the present study, the mortality enhancement of different vegetable extracts obtained from food residues when combined with baculoviruses was evaluated. Extracts from spent coffee (E2), rosehip (E17), asparagus (E28), artichoke (E29), beet stalks (E32) and banana peel (E37) were selected as they increased mortality of Spodoptera littoralis nucleopolyhedrovirus (SpliNPV) in second instar S. littoralis larvae, when comparing with the virus inoculation alone. Extracts were assayed at 1 % w/v. In S. littoralis-SpliNPV system, the selected extracts reduced the median lethal concentration (LC50) of SpliNPV against second instar larvae. The E37 extract presented the highest potentiation, as it reduced the LC50 13.61 times, while the rest of the extracts presented LC50 reductions from 3.71 to 7.72-fold. In Spodoptera exigua-SeMNPV (Spodoptera exigua multiple nucleopolyhedrovirus) system, none of the extracts decreased the LC50 of SeMNPV. In contrast, in Spodoptera frugiperda-SfMNPV (Spodoptera frugiperda multiple nucleopolyhedrovirus) system, E2 showed the greatest potentiating effect. In the heterologous systems, none of the extracts tested increased the effective host range of SfMNPV, AcMNPV (Autographa californica multiple nucleopolyhedrovirus), and MbMNPV (Mamestra brassicae multiple nucleopolyhedrovirus) in second instar S. littoralis larvae. Thus, the viral enhancing effect of VWE was host-pathogen and instar dependent. However, the potentiation effect of the extracts could not be directly related with the antioxidants content of the extracts.

Bioreactor Production Process of Spodoptera frugiperda multiple nucleopolyhedrovirus Biopesticide.

Spodoptera frugiperda (fall armyworm) is one of the most important maize pests in the world and the baculovirus Spodoptera frugiperda multiple nucleopolyhedrovirus (SfMNPV), a natural pathogen of this pest, has been used as a biopesticide for its control. At present, in vivo strategies at the commercial scale are employed by multiplying the virus in the host insect in biofactory facilities; however, in vitro large-scale production is an interesting alternative to overcome the limitations of baculoviruses massal production. This study aimed to develop the process of the SfMNPV in vitro production by evaluating the effects of different multiplicities of infection (MOI) and nutritional supplements, morphological and molecular analysis of the infection on the growth of Sf9 cells and virus production. The Bioreactor Stirred Tank Reactor (STR) approach with glutamine-supplemented Sf-900 III serum free culture medium, combined with the MOI of 1.0, showed the best viral production performance, with a specific productivity above 300 occlusion bodies (OBs)/cell and volumetric productivity of 9.0 × 1011 OBs/L.

Entomopathogens and Parasitoids Allied in Biocontrol: A Systematic Review.

Biological pest control is an environmentally friendly alternative to synthetic pesticides, using organisms such as viruses, bacteria, fungi, and parasitoids. However, efficacy is variable and combining different biocontrol agents could improve success rates. We conducted a systematic review of studies combining a parasitoid with an entomopathogenic microorganism, the first of its kind. We searched in Web of Science and extracted data from 49 publications matching the pre-defined inclusion criteria. Combinations of 36 hymenopteran parasitoids with 17 entomopathogenic microorganisms used to control 31 target pests were found. Trichogramma pretiosum and Encarsia formosa were the most frequently studied parasitoids, while Beauveria bassiana, Metarhizium anisopliae, Lecanicillium muscarium, Bacillus thuringiensis var. kurstaki, the Spodoptera exigua multiple nucleopolyhedrovirus, and the Spodoptera frugiperda multiple nucleopolyhedrovirus were the main microbial agents assessed. Out of 49 parasitoid-microorganism combinations assessed in the laboratory experiments, thirty-eight were reported as compatible and six as incompatible. Timing and dosage of biopesticides played a crucial role, with later application and appropriate dosage minimizing adverse effects on parasitoid development. More research is needed to assess compatibility and efficacy under real-world conditions. Our review provides valuable insights for researchers and practitioners to optimize the combined use of micro- and macroorganisms for effective pest control.

Presence of Spodoptera frugiperda Multiple Nucleopolyhedrovirus (SfMNPV) Occlusion Bodies in Maize Field Soils of Mesoamerica.

The occlusion bodies (OBs) of lepidopteran nucleopolyhedroviruses can persist in soil for extended periods before being transported back on to the foliage for transmission to the host insect. A sensitive insect bioassay technique was used to detect OBs of Spodoptera frugiperda multiple nucleopolyhedrovirus (SfMNPV) in 186 soil samples collected from maize fields in the southern Mexican states of Chiapas, Tabasco, Campeche, Yucatán, and Quintana Roo, as well Belize and Guatemala. Overall, 35 (18.8%) samples proved positive for SfMNPV OBs. The frequency of OB-positive samples varied significantly among Mexican states and countries (p &lt; 0.05). Between 1.7 and 4.4% of S. frugiperda larvae that consumed OB-positive samples died from polyhedrosis disease. Restriction endonuclease analysis using PstI and HindIII confirmed that the soil-derived isolates were strains of SfMNPV and that genetic diversity was evident among the isolates. The prevalence of OB-positive soil samples did not differ with altitude or extension (area) of the maize field, but it was significantly higher in fields with the presence of living maize plants compared to those containing dead plants or crop residues (p &lt; 0.05). Georeferenced soil samples were used to identify soil types on digitized soil maps. Lithosol and Luvisol soils had a higher than average prevalence of OB-positive samples (42-45% positive) (p = 0.006), as did Andosol, Gleysol, and Vertisol soils (33-60% OB-positive), although the sample sizes were small (&lt;5 samples) for the latter three soils. In contrast, Cambisol soils had a lower than average prevalence of OB-positive samples (5% positive). Bioassays on Acrisol, Fluvisol, Phaeozem, and Rendzina soils resulted in intermediate levels of OB-positive samples. We conclude that certain soil types may favor OB persistence and virus-mediated biological pest control. The soil is also likely to provide a valuable source of genetic diversity for the design of virus-based insecticides against this pest.

Response of Doru luteipes (Dermaptera: Forficulidae) to insecticides used in maize crop as a function of its life stage and exposure route.

The present study aimed to evaluate insecticide toxicity to Doru luteipes (Scudder), a major predator of maize pests. Lethal and sublethal effects were assessed on nymphs and adults exposed to the insecticides through contact (maize leaves) and ingestion (prey eggs) routes. Tested insecticides included a biopesticide (Spodoptera frugiperda multiple nucleopolyhedrovirus, SfMNPV), modern (flubendiamide and metaflumizone), and older neurotoxins (imidacloprid + β-cyfluthrin). The imidacloprid/β-cyfluthrin mix was highly toxic (100% mortality) to the predator, regardless of the exposure route and predator stage. Metaflumizone caused mortality higher than 95% and 45% of nymphs and adults. Flubendiamide and SfMNPV were the least toxic insecticides, not differing from the untreated control in any of the assessed endpoints. Adult tibial length did not differ among treatments. Metaflumizone impaired egg consumption by nymphs and walking distance of adult D. luteipes. Overall, the insecticides caused a more pronounced effect on D. luteipes nymphs than on adults and were more toxic by the contact route. From these findings, flubendiamide and SfMNPV are safer for D. luteipes and should head insecticide choice in integrated pest management programs in maize.

Characterization and genomic analyses of a novel alphabaculovirus isolated from the black armyworm, Spodoptera cosmioides (Lepidoptera: Noctuidae)

The black armyworm Spodoptera cosmioides is a pest of increasing importance in Cry1Ac-Bt toxin crops and non-Bt crops of soybean and cotton in Brazil. Here we characterized a baculovirus isolated from extracts of S. cosmioides that died with symptoms of nuclear polyhedrosis. The putative novel virus exhibited polyhedral occlusion bodies (OBs) with virions containing multiple rod-shaped nucleocapsids, characteristic of alphabaculoviruses. The virus isolate was named Spodoptera cosmioides nucleopolyhedrovirus isolate CNPSo-72 (SpcoNPV-CNPSo-72). SpcoNPV-CNPSo-72 was lethal to third-instar S. cosmioides caterpillars but not to S. frugiperda under the tested viral concentrations. Moreover, SpcoNPV-CNPSo-72 contained a circular 147,763 bp long genome and a G + C content of 44.8% with 151 annotated ORFs (10 unique for baculovirus) and five homologous regions (hrs). The 38 currently defined baculovirus core genes were found in the SpcoNPV-CNPSo-72 genome. After phylogenetic analysis, the novel virus was found to be closely related to other members of Alphabaculovirus, especially to the Spodoptera-infecting viruses, which included Spodoptera eridania nucleopolyhedrovirus isolate 251, Spodoptera litura nucleopolyhedrovirus isolate II, Spodoptera exigua multiple nucleopolyhedrovirus isolate US-1, Spodoptera eridania nucleopolyhedrovirus isolate CNPSo-165, and Spodoptera frugiperda multiple nucleopolyhedrovirus isolate 19. Surprisingly, the new baculoviral genome was found to code for a putative arginine-associated tRNA gene with a predicted intronic sequence of 105 nt. The gene was found inside the bjdp CDS. Overall, baculoviruses are pathogens that lethally infect insect larvae and their study allows a better understanding of large DNA virus evolution, which provides important insights for the development and improvement of biological control agents.

Hitching a Ride: Examining the Ability of a Specialist Baculovirus to Translocate through Its Insect Host's Food Plant.

Plant vascular systems can translocate the entomopathogen Bacillus thuringiensis from the soil into plant tissues. However, whether other soil dwelling entomopathogens utilize plant vascular tissue for movement has not yet been fully explored. We used Spodoptera frugiperda multiple nucleopolyhedrovirus (SfMNPV) to evaluate whether baculoviruses, a common entomopathogen and bioinsecticide, can be transported through the plant vascular pathways of Zea mays. We found that our treatments did not allow a sufficient virus translocation into the plant to induce a lethal infection in insects, which was confirmed by a molecular analysis. While other entomopathogens translocate, baculoviruses may not be one of them.

Optimization of In Vivo Production of Spodoptera frugiperda multiple nucleopolyhedrovirus (SfMNPV).

Insect viruses have been used to protect crops and forests worldwide for decades. Among insect viruses, isolates of Spodoptera frugiperda multiple nucleopolyhedrovirus (SfMNPV) have proven potential for the control of Spodoptera frugiperda (J. E. Smith) (FAW)(Lepidoptera: Noctuidae), a pest of many economically essential crops across several continents. Mass production of SfMNPV depends on an in vivo system using host insect rearing. However, many factors can limit its production, including abiotic factors and host characteristics, such as the stage of development and an antagonist intraspecific interaction. Thus, to improve in vivo production, we verified the most suitable larval age to inoculate the virus and the influence of incubation temperature on viral production. Subsequently, cannibal behavior was verified in FAW larvae reared at different densities, while reproducing the conditions of the best treatments. The highest viral yield occurred when FAW larvae were inoculated at 10 and 8days old and incubated at 22°C and 25°C, respectively. Nonetheless, survival (lethal period in days) and cannibal behavior were positively influenced by larval development, which potentially increases the load of contamination and requires larval individualization for these production conditions. In contrast, 4-day-old larvae, which were inoculated and incubated at 31°C, also demonstrated high viral production, with lower rates of cannibalism and death on the same day, thereby showing potential. The information presented in this study is useful for the optimization of the in vivo production systems of SfMNPV.

Successful co-infection of two different baculovirus species in the same cell line reveals a potential strategy for large in vitro production

Baculoviruses have been applied for biocontrol of agricultural pests, such as velvetbean caterpillar (Anticarsia gemmatalis) and fall armyworm (Spodoptera frugiperda). Cell culture is an interesting approach for large-scale production of these viruses. Co-infection of a host cell with two distinct viruses can contribute to reduce costs due to saving cell culture media, bioreactor space and the resulting co-occluded polyhedra may help to reduce final biopesticide costs. The baculovirus Anticarsia gemmatalis multiple nucleopolyhedrovirus (AgMNPV) and Spodoptera frugiperda multiple nucleopolyhedrovirus (SfMNPV) were chosen to test a model for in vitro co-infection in SF21 cells. Different proportions of SfMNPV/AgMNPV were evaluated along three in vitro passages by optical microscopy analysis of cells and real-time PCR (qPCR) of DNA obtained from budded viruses (BVs) and occlusion bodies (OBs). The kinetics of viral protein synthesis was carried out for analysis of the co-infection in first passage and bioassays with the resulting OBs were performed against A. gemmatalis and S. frugiperda larvae. The results demonstrated successful co-infection in these cells. The quantity of SfMNPV and AgMNPV in supernatants and sediments tends to be maintained stable during the three passages, although the amount of AgMNPV was higher than SfMPNV in most of the experiments. Analysis of the kinetics of radiolabed proteins showed that the cell protein synthesis was shut off and two distinct bands of about 30 kDa, regarded to be the polyhedrin of each virus, were strongly detected at 48 and 72 hp.i. Although the pathogenicity of the produced viruses was not completely satisfactory, the bioassays confirmed occurrence of co-infected larvae with disproportional amount of each virus.

Pathogenic Assessment of SfMNPV-Based Biopesticide on Spodoptera frugiperda (Lepidoptera: Noctuidae) Developing on Transgenic Soybean Expressing Cry1Ac Insecticidal Protein.

Pathogenic assessment of a baculovirus-based biopesticide containing Spodoptera frugiperda multiple nucleopolyhedrovirus (SfMNPV: Baculoviridae: Alphabaculovirus) infecting fall armyworm, Spodoptera frugiperda (J. E. Smith, 1797) (Lepidoptera: Noctuidae) is reported. In the bioassays, neonates were infected with different doses of SfMNPV applied on Cry1Ac Bt soybean and non-Bt soybean. Our findings indicated that S. frugiperda neonates did not survive at 10 d post infection or develop into adults on Bt and non-Bt soybean sprayed with the field recommended dose of SfMNPV. In contrast, a proportion of the infected neonates developed into adults when infected with lower doses of SfMNPV (50%, 25%, and 10% of field dose) in both Bt and non-Bt soybean. However, S. frugiperda neonates surviving infection at the lowest virus doses on both soybean varieties showed longer neonate-to-pupa and neonate-to-adult periods, lower larval and pupal weights, reduced fecundity, and increased population suppression. Nevertheless, more pronounced pathogenicity of SfMNPV infecting neonates of S. frugiperda were verified on larvae that developed on Bt soybean. These findings revealed that, beyond mortality, the biopesticide containing SfMNPV also causes significant sublethal pathogenic effects on neonates of S. frugiperda developing on Bt and non-Bt soybean and suggested an additive effect among SfMNPV and Cry1Ac insecticidal protein expressed in Bt soybean.

Genome Sequence of a Spodoptera frugiperda Multiple Nucleopolyhedrovirus Isolated from Fall Armyworm (Spodoptera frugiperda) in Nigeria, West Africa.

ABSTRACTWe report the entire genome sequence of an isolate of Spodoptera frugiperda multiple nucleopolyhedrovirus from Nigeria, West Africa. The genome is 132,710 bp long and contains 144 open reading frames. The GC content is 40.3% and, based on baculovirus species demarcation criteria, the isolate belongs to the species Spodoptera frugiperda multiple nucleopolyhedrovirus.

Differential insecticidal properties of Spodoptera frugiperda multiple nucleopolyhedrovirus isolates against corn-strain and rice-strain fall armyworm, and genomic analysis of three isolates

The fall armyworm, Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae) is a destructive crop pest native to North, Central, and South America that recently has spread to Africa and Asia. Isolates of Spodoptera frugiperda multiple nucleopolyhedrovirus (SfMNPV) have the potential to be developed as low-risk biopesticides for management of fall armyworm, and a commercially available formulation has been developed for control of fall armyworm in North and South America. In this study, the virulence (LC50 and LT50) of several SfMNPV isolates towards larvae of both corn-strain and rice-strain fall armyworm was assessed. Bioassays with corn-strain larvae revealed that the isolates could be organized into fast-killing (LT50 < 56 h post-infection) and slow-killing (LT50 > 68 h post-infection) groups. Rice-strain larvae exhibited narrower ranges of susceptibility to baculovirus infection and of survival times in bioassays with different isolates. Two SfMNPV isolates with rapid speeds of kill (SfMNPV-459 from Colombia and SfMNPV-1197 from Georgia, USA) along with an isolate that killed corn-strain at relatively low concentrations (SfMNPV-281 from Georgia) were selected for the complete determination of their genome sequences. The SfMNPV-1197 genome sequence shared high sequence identity with genomes of a Nicaraguan isolate, while SfMNPV-281 formed a separate clade with a USA and a Brazilian isolate in phylogenetic trees. The SfMNPV-459 sequence was more divergent with the lowest genome sequence identities in pairwise alignments with other sequenced SfMNPV genomes, and was not grouped reliably with either the 1197 clade or the 281 clade. SfMNPV-459 contained homologs of two ORFs that were unique to another Colombian isolate, but these isolates were not placed in the same clade in phylogenetic trees. This study identifies isolates with superior properties for control of fall armyworm and adds to our knowledge of the genetics of SfMNPV.

Genomic diversity in a population of Spodoptera frugiperda nucleopolyhedrovirus.

Spodoptera frugiperda multiple nucleopolyhedrovirus (SfMNPV) represents a strong candidate to develop environmental-friendly pesticides against the fall armyworm (Spodoptera frugiperda), a widespread pest that poses a severe threat to different crops around the world. To date, SfMNPV genomic diversity of different isolates has been mainly studied by means of restriction pattern analyses and by sequencing of the egt region. Here, the genomic diversity present inside an isolate of SfMNPV was explored using high-throughput sequencing for the first time. We identified 704 intrahost single nucleotide variants, from which 184 are nonsynonymous mutations distributed among 82 different coding sequences. We detected several structural variants affecting SfMNPV genome, including two previously reported deletions inside the egt region. A comparative analysis between polymorphisms present in different SfMNPV isolates and our intraisolate diversity data suggests that coding regions with higher genetic diversity are associated with oral infectivity or unknown functions. In this context, through molecular evolution studies we provide evidence of diversifying selection acting on sf29, a putative collagenase which could contribute to the oral infectivity of SfMNPV. Overall, our results contribute to deepen our understanding of the coevolution between SfMNPV and the fall armyworm and will be useful to improve the applicability of this virus as a biological control agent.

Molecular and Biological Characterization of Spodoptera frugiperda Multiple Nucleopolyhedrovirus Field Isolate and Genotypes from China.

Simple SummaryThe fall armyworm is a notorious lepidopteran pest that consumes many economically important crops. Its recent invasion into China threatens crops in over 19 provinces. This species is susceptible to its homologous nucleopolyhedrovirus (Spodoptera frugiperda multiple nucleopolyhedrovirus, or SfMNPV). Selection of indigenous isolates that are adaptable in each geographical region is important for developing a virus-based pesticide. In this study, an SfMNPV field isolate was obtained from a natural population of the fall armyworm in Hubei, China. Two genotypes were cloned from the field isolate, and one genotype, SfHub-A, which had similar activity to the field isolate and produced significantly more progeny viruses, was considered to be a suitable strain for the commercial production of SfMNPV. This information will be valuable for developing a virus-based pesticide against fall armyworm in China.The fall armyworm, Spodoptera frugiperda, is a new invading pest in China. The baculovirus Spodoptera frugiperda multiple nucleopolyhedrovirus (SfMNPV) is a pathogenic agent of the fall armyworm and a potential agent for its control in integrated pest management strategies. In this work, we analyze the molecular and biological characteristics of an SfMNPV isolate collected from maize in China (SfMNPV-Hub). Two genotypes were further isolated from SfMNPV-Hub by an in vivo cloning method. The PstI profile of one genotype (SfHub-A) was similar to genotype A of the SfMNPV Colombian isolate, and the other (SfHub-E) was similar to genotype E of the Colombian isolate. The bioactivity of SfHub-A against second-instar S. frugiperda larvae was not significantly different from that of SfMNPV-Hub, whereas SfHub-E was 2.7–5.5 fold less potent than SfMNPV-Hub. The speed of kill of SfHub-E was quicker than SfMNPV-Hub, while SfHub-A acted slower than SfMNPV-Hub. Occlusion body (OB) production of SfHub-A in an S. frugiperda cadaver was significantly higher than that of SfMNPV-Hub, while SfHub-E yielded far fewer occlusion bodies (OBs) in the host larvae. These results provide basic information for developing a virus-based pesticide against the invading pest S. frugiperda.

Biological characterization of two Spodoptera frugiperda nucleopolyhedrovirus isolates from Mexico and evaluation of one isolate in a small-scale field trial

This study describes the biological activity of two Spodoptera frugiperda multiple nucleocapsid nucleopolyhedrovirus (SfMNPV) isolates recovered from the soil of maize crops in the states of Yucatán and Chiapas, Mexico (Sf-YUC and Sf-CHI). The biological activity was determined for four Spodoptera frugiperda (J. E. Smith) (Lepidoptera: Noctuidae) field populations: Sf-Motozintla, Sf-Erongaricuaro, Sf-Abasolo, and Sf-Culiacancito. As a reference, a laboratory colony (Sf-Lab) was used. Biological characterization was compared with that for a characterized SfMNPV isolate from Nicaragua (Sf-NIC). The LC50 values for both the Sf-NIC and Sf-CHI isolates did not differ in any of the insect populations tested. In contrast, the Sf-YUC isolate was less active than the Sf-NIC isolate in the Sf-Motozintla population, but this isolate was more active in the Sf-Erongaricuaro and Sf-Abasolo populations. The killing speed and OB productivity were variable among isolates in each insect population. A small-scale field trial was performed to evaluate the degree of pest control achieved by the Sf-YUC isolate, applied at a rate of 3 × 1012 OBs/ha, in maize grown in central Mexico. The larval mortality caused by the virus was 58%, 78%, and 84% at 2, 5, and 7 d post application, respectively. At 7 d post application, the incidence of insect parasitoids in the virus treatment was significantly lower than in the control. In conclusion, the insecticidal characteristics of both Mexican isolates (Sf-CHI and Sf-YUC) varied according to their insect population. In addition, the Sf-YUC isolate may be suitable as the basis for a biopesticide for the control of S. frugiperda in Mexico.

Vertical dispersal of nucleopolyhedrovirus occlusion bodies in soil by the earthworm Amynthas gracilus: a field-based estimation

ABSTRACTThe soil is the most important environmental reservoir for nucleopolyhedrovirus occlusion bodies (OBs). We employed a diet + soil bioassay technique to demonstrate that the earthworm Amynthas gracilus was capable of vertical transport of Spodoptera frugiperda multiple nucleopolyhedrovirus (SfMNPV) occlusion bodies (OBs) under field conditions. Incubation of OBs with earthworms in sand did not adversely affect the prevalence of virus-induced mortality, but variation in insect mortality was markedly increased, possibly due to changes in the particle size distribution following earthworm processing of OB-contaminated sand. We conclude that earthworms are likely to interact frequently with soil OB populations.