The fall armyworm (FAW) Spodoptera frugiperda is thought to have undergone a rapid ′west-to-east′ spread since 2016 when it was first identified in western Africa. Between 2018 and 2020, it was also recorded from South Asia (SA), Southeast Asia (SEA), East Asia (EA), and Pacific/Australia (PA). Population genomic analyses enables the understanding of pathways, population sources, and gene flow in this notorious agricultural pest species. Using neutral single nucleotide polymorphic (SNP) DNA markers, we detected genome introgression that suggested most populations were overwhelmingly C- and R-strain hybrids. SNP and mitochondrial DNA markers identified multiple introductions that were most parsimoniously explained by anthropogenic-assisted spread, i.e., associated with international trade of live/fresh plants and plant products, and involved ′bridgehead populations′ in countries to enable successful pest establishment in neighbouring countries. Distinct population genomic signatures between Myanmar and China do not support the ′African origin spread′ nor the ′Myanmar source population to China′ hypotheses. Significant genetic differentiation between populations from different Australian states supported multiple pathways involving distinct SEA populations. Our study identified Asia as a biosecurity hotspot and a FAW genetic melting pot, and demonstrated the use of genome analysis to disentangle preventable human-assisted pest introductions from unpreventable natural pest spread

The fall armyworm (FAW) Spodoptera frugiperda (Smith; Lepidoptera: Noctuidae) is present in over 70 countries in Africa, Asia, and Oceania. Its rapid dispersal since 2016 when it was first reported in western Africa, and associated devastation to agricultural productivity, highlight the challenges posed by this pest. Currently, its management largely relies on insecticide sprays and transgenic Bacillus thuringiensis toxins, therefore understanding their responses to these agents and characteristics of any resistance genes enables adaptive strategies. In Australia, S. frugiperda was reported at the end of January 2020 in northern Queensland and by March 2020, also in northern Western Australia. As an urgent first response we undertook bioassays on two Australian populations, one each from these initial points of establishment. To assist with preliminary sensitivity assessment, two endemic noctuid pest species, Helicoverpa armigera (Hübner; Lepidoptera, Noctuidae) and Spodoptera litura (Fabricius; Lepidoptera, Noctuidae), were concurrently screened to obtain larval LC50 estimates against various insecticides. We characterized known resistance alleles from the VGSC, ACE-1, RyR, and ABCC2 genes to compare with published allele frequencies and bioassay responses from native and invasive S. frugiperda populations. An approximately 10× LC50 difference for indoxacarb was detected between Australian populations, which was approximately 28× higher than that reported from an Indian population. Characterization of ACE-1 and VGSC alleles provided further evidence of multiple introductions in Asia, and multiple pathways involving genetically distinct individuals in Australia. The preliminary bioassay results and resistance allele patterns from invasive S. frugiperda populations suggest multiple introductions have contributed to the pest’s spread and challenge the axiom of its rapid ‘west-to-east’ spread.

Larvae of the canegrub Lepidiota reuleauxi have become pests of commercial sugarcane in Papua New Guinea. The biology of L . reuleauxi was studied under field and laboratory conditions. The species is univoltine. Adult activity commenced soon after the onset of the rainy season. Adults emerged just before dusk for mating. Males aggregated, probably in response to pheromonal cues from females. The adults (both sexes) lived for 3-4 weeks but did not appear to feed. Larvae require live root material as an essential dietary component. Other larval food plants were Imperata cylindrica, Saccharum spontaneum, Panicum maximum, Pennisetum purpureum and Zea mays. The biology of L. reuleauxi is compared with those of other Lepidiota spp. attacking sugarcane.

The fall armyworm Spodoptera frugiperda is present in over 70 countries in Africa, Asia, and Oceania. Its rapid dispersal since 2016 since first reported in western Africa, and associated devastation to agricultural productivity, highlight the challenges posed by this pest. Currently, its management largely relies on insecticide sprays and transgenic Bacillus thuringiensis toxins, therefore understanding their responses to these agents and characteristics of any resistance genes enables adaptive strategies. In Australia, S. frugiperda was reported at the end of January 2020 in northern Queensland and by March 2020, also in northern Western Australia. We undertook bioassays on two Australian populations, one each from these initial points of establishment. To assist with resistance response interpretation, two related endemic noctuid pest species, Helicoverpa armigera and Spodoptera litura, were concurrently screened to obtained LC50 estimates for larvae against a range of insecticides. We characterised known resistance alleles from the VGSC, ACE-1, RyR, and ABCC2 genes for five populations to compared with published allele frequencies and bioassay responses from native and invasive S. frugiperda populations. An approximately 10x LC50 difference for indoxacarb was detected between Australian populations, which was approximately 28x higher than an Indian population. Characterisation of ACE-1 and VGSC alleles provided further evidence of multiple introductions in Asia, and multiple pathways involving genetically distinct individuals into Australia. Bioassay results and resistance allele patterns from invasive S. frugiperda populations therefore suggest multiple introduction events have contributed to the pest′s spread in the Old World, and challenge the axiom of its rapid ′west-to-east′ spread.

No abstract