Resistance Bioassays and Allele Characterization Inform Analysis of Spodoptera frugiperda (Lepidoptera: Noctuidae) Introduction Pathways in Asia and Australia

Abstract

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.

The Fall Armyworm and Larger Grain Borer Pest Invasions in Africa: Drivers, Impacts and Implications for Food Systems

“…Exceptionally high fecundity allows for the rapid establishment of a species post-invasion [ 44 , 178 ]. In addition, adults have been known to migrate several hundreds of kilometres [ 179 , 180 ]. The adult moths can fly continuously for over 24 h and cover over 400 km through self-powered flight [ 181 ].…”

“…The invasion success of S. frugiperda has been attributed to high parental propagules and multivoltine nature [ 14 , 124 , 182 , 186 ]. In addition to the high genetic diversity found in this species, human-assisted long-distance movements can reciprocate introductions of genotypes from invasive populations to native populations [ 180 ]. Spodoptera frugiperda can feed on any part of the host plant, e.g., on leaves, tassels and ears on or before the soft dough stage.…”

Virulence of Beauveria sp. and Metarhizium sp. fungi towards fall armyworm (Spodoptera frugiperda)

“…Smith) (Lepidoptera: Noctuidae), is an invasive moth species that was detected in the Torres Strait Islands, Australia, in late January 2020 (Tay et al 2023a ). By the end of 2020, it had been detected widely across mainland Australia (International Plant Protection Convention 2020 ; Government of Western Australia 2021 ; Tay et al 2022a ). S. frugiperda is native to the tropical regions of the American continents (Southern United States to Argentina) where it is a serious pest of agricultural production (Capinera 1969 ; Andrews 1980 ).…”

“…It is also able to disperse over long distances, especially with prevailing winds, when hosts are limiting (Westbrook et al 2016 ), and in response to season and weather (Westbrook et al 2019 ). Due to economic damage, polyphagy, fecundity, and dispersion from mobility, and transportation of contaminated live plant product (Tay et al 2022b , 2023b ), S. frugiperda has quickly become a major threat to agricultural production across its invasive ranges (Goergen et al 2016 ; Cock et al 2017 ; Ganiger et al 2018 ; du Plessis et al 2018 ; Trisyono et al 2019 ; Agboyi et al 2020 ; Fan et al 2020 ; Kandel and Poudel 2020 ; Lee et al 2020 ; Piggott et al 2021 ; Zaimi et al 2021 ; Zhou et al 2021 ; Tay et al 2022a ; Wu et al 2022 ). There is now high demand for effective and sustainable management tools to reduce economic impact of this invasive pest.…”

“…Globally, management strategies for S. frugiperda have relied heavily on synthetic insecticides and genetically modified Bt crops, which contributed to the development of insecticide resistance (Togola et al 2018 ). S. frugiperda populations showed resistance to several synthetic insecticides in both their native range (Yu et al 2003 ; León-García et al 2012 ; Garlet et al 2021 ) and in recently colonised regions (e.g., indoxacarb, chlorpyrifos, and malathion, Zhao et al 2020 ; Zhang et al 2020 ; Kulye et al 2021 ; to methomyl, Tay et al 2022a ). Additionally, resistance to Bt proteins including various Cry1 (Storer et al 2010 ; Jakka et al 2014 ; Huang et al 2014 ; Gutierrez et al 2015 ; Monnerat et al 2015 ; Leite et al 2016 ), Cry2Ab2 (Niu et al 2016 ), and Vip3Ac (Yang et al 2018 ) have also been detected in their native range.…”