Source Regions of the First Immigration of Fall Armyworm, Spodoptera frugiperda (Lepidoptera: Noctuidae) Invading Australia

SIMPLE SUMMARY: The fall armyworm, Spodoptera frugiperda, is a serious invasive, crop-destroying pest, which is the subject of a global warning from the United Nations Food and Agriculture Organization (FAO). The surprisingly rapid spread of fall armyworm and its significant capacity to generate high-yield losses has attracted increased attention worldwide. In January 2020, fall armyworm was first confirmed in Torres Strait (Saibai and Erub Islands) and mainland Australia (Bamaga). However, the possible source region of the first immigration of fall armyworm was still obscure. A better understanding of the migration paths and the source regions of fall armyworm immigrants, will be useful for the monitoring and early warning of this pest in Australia. The migratory paths and wind systems for the first case of the immigration of fall armyworm invading Australia were simulated using a three-dimensional trajectory analysis program. This study has confirmed that the immigration of fall armyworm to Australia was most likely from Sulawesi and Moluccas Islands of Indonesia. ABSTRACT: Fall armyworm is recognized as one of most highly destructive global agricultural pests. In January 2020, it had first invaded Australia, posing a significant risk to its biosecurity, food security, and agricultural productivity. In this study, the migration paths and wind systems for the case of fall armyworm invading Australia were analyzed using a three-dimensional trajectory simulation approach, combined with its flight behavior and NCEP meteorological reanalysis data. The analysis showed that fall armyworm in Torres Strait most likely came from surrounding islands of central Indonesia on two occasions via wind migration. Specifically, fall armyworm moths detected on Saibai and Erub Islands might have arrived from southern Sulawesi Island, Indonesia, between January 15 and 16. The fall armyworm in Bamaga most likely arrived from the islands around Arafura Sea and Sulawesi Island of Indonesia, between January 26 and 27. The high risk period for the invasion of fall armyworm is only likely to have occurred in January–February due to monsoon winds, which were conducive to flight across the Timor Sea towards Australia. This case study is the first to confirm the immigration paths and timing of fall armyworm from Indonesia to Australia via its surrounding islands.