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Spodoptera frugiperda (Lepidoptera: Noctuidae) host-plant variants: two host strains or two distinct species?

ABSTRACT: The moth Spodoptera frugiperda is a well-known pest of crops throughout the Americas, which consists of two strains adapted to different host-plants: the first feeds preferentially on corn, cotton and sorghum whereas the second is more associated with rice and several pasture grasses. Though morphologically indistinguishable, they exhibit differences in their mating behavior, pheromone compositions, and show development variability according to the host-plant. Though the latter suggest that both strains are different species, this issue is still highly controversial because hybrids naturally occur in the wild, not to mention the discrepancies among published results concerning mating success between the two strains. In order to clarify the status of the two host-plant strains of S. frugiperda, we analyze features that possibly reflect the level of post-zygotic isolation: (1) first generation (F1) hybrid lethality and sterility; (2) patterns of meiotic segregation of hybrids in reciprocal second generation (F2), as compared to the meiosis of the two parental strains. We found a significant reduction of mating success in F1 in one direction of the cross and a high level of microsatellite markers showing transmission ratio distortion in the F2 progeny. Our results support the existence of post-zygotic reproductive isolation between the two laboratory strains and are in accordance with the marked level of genetic differentiation that was recovered between individuals of the two strains collected from the field. Altogether these results provide additional evidence in favor of a sibling species status for the two strains.

SUBMITTER: Dumas P

PROVIDER: S-EPMC4419160 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:BackgroundThe evolution of insecticide resistance in Spodoptera frugiperda (Lepidoptera: Noctuidae) has resulted in large economic losses and disturbances to the environment and agroecosystems. Resistance to lufenuron, a chitin biosynthesis inhibitor insecticide, was recently documented in Brazilian populations of S. frugiperda. Thus, we utilized large-scale cDNA sequencing (RNA-Seq analysis) to compare the pattern of gene expression between lufenuron-resistant (LUF-R) and susceptible (LUF-S) S. larvae in an attempt to identify the molecular basis behind the resistance mechanism(s) of S. frugiperda to this insecticide.ResultsA transcriptome was assembled using approximately 19.6 million 100 bp-long single-end reads, which generated 18,506 transcripts with a N50 of 996 bp. A search against the NCBI non-redundant database generated 51.1% (9,457) functionally annotated transcripts. A large portion of the alignments were homologous to insects, with the majority (45%) being similar to sequences of Bombyx mori (Lepidoptera: Bombycidae). Moreover, 10% of the alignments were similar to sequences of various species of Spodoptera (Lepidoptera: Noctuidae), with 3% of them being similar to sequences of S. frugiperda. A comparative analysis of the gene expression between LUF-R and LUF-S S. frugiperda larvae identified 940 differentially expressed transcripts (p ≤ 0.05, t-test; fold change ≥ 4). Six of them were associated with cuticle metabolism. Of those, four were overexpressed in LUF-R larvae. The machinery involved with the detoxification process was represented by 35 differentially expressed transcripts; 24 of them belonging to P450 monooxygenases, four to glutathione-S-transferases, six to carboxylases and one to sulfotransferases. RNA-Seq analysis was validated for a number of selected candidate transcripts by using quantitative real time PCR (qPCR).ConclusionsThe gene expression profile of LUF-R larvae of S. frugiperda differs from LUF-S larvae. In general, gene expression is much higher in resistant larvae when compared to the susceptible ones, particularly for those genes involved with pathways for xenobiotic detoxification, mainly represented by P450 monooxygenases transcripts. Our data indicate that enzymes involved with the detoxification process, and mostly the P450, are one of the resistance mechanisms employed by the LUF-R S. frugiperda larvae against lufenuron.

Project description:The aim of this experiment was to compare the transciptome of the fall armyworm (Spodoptera frugiperda) strain SUS (a laboratory insecticide-susceptible standard) with organophosphate (OP) and pyrethroid (PYR) resistant strains were collected in cornfields located in Minas Gerais and Mato Grosso States, Brazil, in 2008 and maintained in the laboratory under selection with chlorpyrifos (at increasing discriminating doses from 100 up to 400 M-BM-5g of insecticide/g of insect in a topical bioassay) or lambda-cyhalothrin (from 8.4 up to 27 M-BM-5g of insecticide/g of insect) respectively The custom microarray used in this study was designed using the Agilent eArray platform (Agilent Technologies). A SurePrint HD (8M-CM-^W15k) expression array was designed using the base composition and the best probe methodologies to design sense orientation 60-mer probes with a 3M-bM-^@M-2 bias. The FAW EST database (SPODOBASE) was used as the reference transcriptome (Negre, Hotelier et al. 2006). These sequences are derived from 8 cDNA libraries as follows: Sf1F: Fat body, Sf1H: Hemocyte, Sf1M: Midgut, Sf1P: Pool of various tissues, Sf2H: Immune Challenged hemocytes, Sf2L: Sf21 Cell lines sequences, Sf2M: Xenobiotic Induced Midgut and Sf9L: Sf9 cell lines sequences. All assembled contigs and singlets were kindly sent by the website maintainers. The BLAST2GO software v.2.3.1 (http://www.blast2go.org) was used to annotate the EST database. 60-mer probes were designed for all 7,552 assembled contigs and 5,519 annotated singlets (BlastX), totaling 13,071 sequences. For contigs encoding detoxification enzymes (P450s, GSTs and CEs) three probes were designed. Additional probe groups for 15 control genes were also included. For reference all sequences are included in the zip file with array data. References: Negre, V., T. Hotelier, et al. (2006). "SPODOBASE : an EST database for the lepidopteran crop pest Spodoptera." BMC Bioinformatics 7: 322. Two-condition experiment. Slide 1: SUS vs. OP S. fugiperda strains. Slide 2: SUS vs. PYR S. fugiperda strains. Biological replicates: 4 pools of RNA extracted from four pools of 5 second instar larvae. Technical Replicates: None, the biological replicates incorporated a dye swap. Total replication: four replicates for each strain.

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Spodoptera frugiperda (Lepidoptera: Noctuidae) host-plant variants: two host strains or two distinct species?

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