Spodoptera frugiperda: Ecology, Evolution, and Management Options of an Invasive Species

The fall armyworm (FAW), Spodoptera frugiperda (Lepidoptera, Noctuidae), is a well-known agricultural pest in its native range, North and South America, and has become a major invasive pest around the globe in the past decade. In this review, we provide an overview to update what is known about S. frugiperda in its native geographic ranges. This is followed by discussion of studies from the invaded areas to gain insights into S. frugiperda's ecology, specifically its reproductive biology, host plant use, status of insecticide resistance alleles, and biocontrol methods in native and invasive regions. We show that reference to host strains is uninformative in the invasive populations because multidirectional introduction events likely underpinned its recent rapid spread. Given that recent genomic analyses show that FAW is much more diverse than was previously assumed, and natural selection forces likely differ geographically, region-specific approaches will be needed to control this global pest.

Whole-genome sequencing to detect mutations associated with resistance to insecticides and Bt proteins in Spodoptera frugiperda

The fall armyworm (FAW), Spodoptera frugiperda, is a major pest native to the Americas that has recently invaded the Old World. Point mutations in the target-site proteins acetylcholinesterase-1 (ace-1), voltage-gated sodium channel (VGSC) and ryanodine receptor (RyR) have been identified in S. frugiperda as major resistance mechanisms to organophosphate, pyrethroid and diamide insecticides respectively. Mutations in the adenosine triphosphate-binding cassette transporter C2 gene (ABCC2) have also been identified to confer resistance to Cry1F protein. In this study, we applied a whole-genome sequencing (WGS) approach to identify point mutations in the target-site genes in 150 FAW individuals collected from China, Malawi, Uganda and Brazil. This approach revealed three amino acid substitutions (A201S, G227A and F290V) of S. frugiperda ace-1, which are known to be associated with organophosphate resistance. The Brazilian population had all three ace-1 point mutations and the 227A allele (mean frequency = 0.54) was the most common. Populations from China, Malawi and Uganda harbored two of the three ace-1 point mutations (A201S and F290V) with the 290V allele (0.47-0.58) as the dominant allele. Point mutations in VGSC (T929I, L932F and L1014F) and RyR (I4790M and G4946E) were not detected in any of the 150 individuals. A novel 12-bp insertion mutation in exon 15 of the ABCC2 gene was identified in some of the Brazilian individuals but absent in the invasive populations. Our results not only demonstrate robustness of the WGS-based genomic approach for detection of resistance mutations, but also provide insights for improvement of resistance management tactics in S. frugiperda.

Mitochondrial DNA genomes of five major Helicoverpa pest species from the Old and New Worlds (Lepidoptera: Noctuidae)

Five species of noctuid moths, Helicoverpa armigera, H. punctigera, H. assulta, H. zea, and H. gelotopoeon, are major agricultural pests inhabiting various and often overlapping global distributions. Visual identification of these species requires a great deal of expertise and misidentification can have repercussions for pest management and agricultural biosecurity. Here, we report on the complete mitochondrial genomes of H. assulta assulta and H. assulta afra, H. gelotopoeon, H. punctigera, H. zea, and H. armigera armigera and H. armigera conferta' assembled from high-throughput sequencing data. This study significantly increases the mitogenome resources for these five agricultural pests with sequences assembled from across different continents, including an H. armigera individual collected from an invasive population in Brazil. We infer the phylogenetic relationships of these five Helicoverpa species based on the 13 mitochondrial DNA protein-coding genes (PCG's) and show that two publicly available mitogenomes of H. assulta (KP015198 and KR149448) have been misidentified or incorrectly assembled. We further consolidate existing PCR-RFLP methods to cover all five Helicoverpa pest species, providing an updated method that will contribute to species differentiation and to future monitoring efforts of Helicoverpa pest species across different continents. We discuss the value of Helicoverpa mitogenomes to assist with species identification in view of the context of the rapid spread of H. armigera in the New World. With this work, we provide the molecular resources necessary for future studies of the evolutionary history and ecology of these species.

Mitochondrial DNA and trade data support multiple origins of Helicoverpa armigera (Lepidoptera, Noctuidae) in Brazil

The Old World bollworm Helicoverpa armigera is now established in Brazil but efforts to identify incursion origin(s) and pathway(s) have met with limited success due to the patchiness of available data. Using international agricultural/horticultural commodity trade data and mitochondrial DNA (mtDNA) cytochrome oxidase I (COI) and cytochrome b (Cyt b) gene markers, we inferred the origins and incursion pathways into Brazil. We detected 20 mtDNA haplotypes from six Brazilian states, eight of which were new to our 97 global COI-Cyt b haplotype database. Direct sequence matches indicated five Brazilian haplotypes had Asian, African, and European origins. We identified 45 parsimoniously informative sites and multiple substitutions per site within the concatenated (945 bp) nucleotide dataset, implying that probabilistic phylogenetic analysis methods are needed. High diversity and signatures of uniquely shared haplotypes with diverse localities combined with the trade data suggested multiple incursions and introduction origins in Brazil. Increasing agricultural/horticultural trade activities between the Old and New Worlds represents a significant biosecurity risk factor. Identifying pest origins will enable resistance profiling that reflects countries of origin to be included when developing a resistance management strategy, while identifying incursion pathways will improve biosecurity protocols and risk analysis at biosecurity hotspots including national ports.

The complete mitochondrial DNA genome of a Chloridea (Heliothis) subflexa (Lepidoptera: Noctuidae) morpho-species

We investigate the complete mitogenome of a pheromone-trapped morpho-species of Chloridea subflexa from Brazil (initially identified by the Sanger sequencing of partial mtCOI gene) as 15 323 bp (KT598688) via next generation sequencing platform. The mitogenome has an A/T rich base composition (A: 40.4%; T: 40.3%; C: 11.5%; G: 7.8%), and included 13 protein-coding genes (PCGs), 22 tRNAs, 2 ribosomal RNAs and a putative replication region (ca. 323 bp). All PCGs start with a methionine (M) amino acid except the COI gene which has an arginine (R). The trnL2 and trn-Lys genes were partially embedded within the COII gene, while the trn-His gene was completely embedded within the ND4 gene. All PCGs ends with the "TAA" stop codon except ND3 which has a "TAG" stop codon.