Spodoptera frugiperda (J. E. Smith) (Lepidoptera: Noctuidae), native to the tropical and subtropical regions of the Americas, is a major agricultural pest widely distributed in the American continent1. Since 2016, the insect has invaded more than 60 countries and regions, including Africa, Asia, and Oceania2. In December 2018, S. frugiperda adults invaded Yunnan, China, from Myanmar3. Moreover, on January 11, 2019, its larvae were first witnessed damaging maize in Jiangcheng County, Yunnan Province, China. After that, S. frugiperda, with its powerful long-distance migration ability, spread rapidly and caused damage across the country2,4. As of August 31, 2020, S. frugiperda has been found in 1,338 counties of 27 provinces nationwide. Among them, only adult insects were seen in 21 counties of Ningxia, Liaoning, Inner Mongolia, Beijing, and Tianjin. In a survey in late August, the larvae were found in 865 counties of 22 provinces, and the area where larvae occurred was 3.68 million mu5-7. Thus, it is essential to clarify the potential distribution of S. frugiperda in China for early warning as well as comprehensive prevention and control2.
S. frugiperda has a strong flight capacity. Under suitable wind conditions, S. frugiperda adult can even travel 1,600 km within 30 h; in China, S. frugiperda is also predicted to migrate long distances8,9. S. frugiperda has a wide host range and can damage more than 300 species of plants, including rice, sorghum, millet, sugarcane, vegetable crops, and cotton. The larvae mainly feed on tender tips, drill the base of the stem, and damage the maize ears, resulting in reduced yield or even no harvest10. If proper control measures are not taken, S. frugiperda will cause severe yield losses. Based on the feeding preferences for host plants, S. frugiperda can be divided into two haplotypes: the maize strain, which mainly feeds on and harms maize, cotton, and sorghum; the rice strain, which mainly feeds on and harms rice and various forage grasses11. S. frugiperda that has invaded China belongs to the maize strain and damages maize mainly by feeding them in summer7,12. In the winter of 2019, S. frugiperda was found to invade in partial areas by feeding on wheat and barley13and in Guangxi and Yunnan by infesting sugarcane14. S. frugiperda is highly adaptable to environments and highly reproductive. Female S. frugiperdas can mate and spawn in a high frequency. Up to 2,300 eggs can be spawned at a time, depending on their nutritional conditions. In China, since S. frugiperda poses a serious long-term threat to the security of national food production, it is therefore classified as a major emergent pest on maize8.
MaxEnt is a species distribution prediction model based on the maximum entropy theory and has been widely used due to its short running time, user-friendly operation, and stable running results. In recent years, using this model, global searchers have systematically studied pests such as Drosophila melanogastes15, Sirex noctilio3, batocera lineolata16, and S. frugiperda. Using the MaxEnt model and ArcGIS, researchers have predicted the potentially suitable area of S. frugiperda in Yunnan, China17. Besides, Several studies have shown the potential distribution of S. frugiperda in Central Asia18. Model prediction results well simulated the potential distribution of S. frugiperda, which is consistent with the actual occurrence. S. frugiperda occurs less frequently in the irrigated areas of Northwest China (such as Xinjiang and Tibet), and the prediction shows a reduced overlap and less risk. The potential distribution of S. frugiperda was explored using limiting environmental factors and the collection model prediction scheme19. However, their prediction results lack reference value, especially for the Middle East and East Asia. The potential distribution of S. frugiperda in Central Asia and China have been simulated, with uncertainties in single model predictions (MaxEnt model). Regions such as Liaoning, Hebei, Beijing, Tianjin, Shanxi, Shaanxi, Inner Mongolia, Ningxia, Gansu, Qinghai, and Xinjiang are suitable distribution areas for S. frugiperda in spring, summer, and autumn18,20.
China is one of the maize-producing countries, and maize is an important food crop and cash crop for China. Northwest China is a major production area of wheat and maize, so it is a crucial prevention area for S. frugiperda. On May 31, 2019, S. frugiperda was first discovered in Yang County, Shaanxi Province. After that, damagze occurred in 63 counties of this province21. On July 2, 2019, S. frugiperda larvae were investigated for the first time in summer maize fields in Duanheba Village, Liangshui Township, Wudu District, Gansu Province22. Although S. frugiperda has not caused serious damage in these regions, it is imperative to clarify the potential geographic distribution of S. frugiperda in Northwest China to guide early warning as well as prevention and control. This study aims to provide a theoretical basis for the further control of S. frugiperda in China.