Journal of Insect Science, (2019) 19(1): 11; 1–9 doi: 10.1093/jisesa/iez002 Research Identifying Immigrating Sogatella furcifera (Hemiptera: Delphacidae) Using Field Cages: A Case Study in the Yuanjiang (Red River) Valley of Yunnan, China Shao-Ji Hu,1,2,8, Li-Min Dong,3,8 Wen-Xin Wang,4 Sui-Yun Chen,5,6 and Hui Ye 3,7 1Institute of International Rivers and Eco-security, Yunnan University, Kunming, 650500, China, 2Yunnan Key Laboratory of International Rivers and Transboundary Eco-security, Yunnan University, Kunming, 650500, China, 3School of Agriculture, Yunnan University, Kunming, 650500, China, 4Yuanjiang Plant Protection and Quarantine Station, Yuanjiang, 653300, China, 5Biocontrol Engineering Research Centre of Crop Disease & Pest, Yunnan University, Kunming, 650500, China, 6Biocontrol Engineering Research Centre of Plant Disease & Pest, Yunnan University, Kunming, 650500, China, and 7Corresponding author, e-mail: [email protected] 8Joint first authors. Subject Editor: Phyllis Weintraub Received 19 July, 2018; Editorial decision 3 January, 2019 Abstract The white-backed planthopper, Sogatella furcifera (Horváth), is a devastating migratory rice pest in South China; lack of effective methods to identify immigrating populations is the main cause of difficulties in outbreak forecasting, active prevention, and control. The current study set up field cages (2 × 2 × 3 m each, US-80 standard nylon mesh) in both early- and mid-season paddies in Yuanjiang (Red River) Valley in Yunnan, China, in 2012 and 2014. The immigrating population was successfully separated from the local population of S. furcifera and identified using statistical comparisons. The findings showed that densities of macropterous adults outside the cages were all significantly higher than those inside the cages on both early- and mid-season rice in both years, whereas the densities of young nymphs and old nymphs showed no significant differences. This indicated that immigrations were occurring, the earliest of which occurred on early-season rice in early May and reached its peak in mid-late May before a rapid collapse in both years. In contrast, the immigration on mid-season rice showed a continuous decline or fluctuation throughout the entire period. Analyses demonstrated that the migration process ofS. furcifera in the Yuanjiang Valley features continuous immigration from the adjacent southern parts of Yunnan, which may represent most migration events in Yunnan during the outbreak period of a year. The findings of this case study could benefit our understanding of planthopper migration and outbreaks in other parts of China, especially where the outbreak pattern is very different from Yunnan. Key words: migratory rice pest, planthopper, population density, demographic structure, field cage The white-backed planthopper, Sogatella furcifera (Horváth), mountain ranges and deep valleys (Hu 2013; Zhao et al. 2014; Wu is a serious pest on Asian cultivated rice, Oryza sativa L. in et al. 2017, 2018). South China and North Indochina (Catindig et al. 2009; Cheng Light trapping and field surveys are two methods applied in 2009, 2015). Migratory behavior, high fecundity, and exponen- the routine monitoring of S. furcifera in China, as described in tial population growth are the main causes of disastrous yield ‘National Standard of the People’s Republic of China (GB/T 15794- loss as well as the difficulty in performing accurate forecast and 2009): Rules of Investigation and Forecast for the Rice Planthopper effective prevention (Gui et al. 2008; Cheng 2009; Hu et al. (Nilaparvata lugens Stål and Sogatella furcifera (Horváth)’ (AQSIQ 2014, 2017). and SAC 2009). Light trapping can detect large-scale and abrupt It is generally accepted that, in South China, the northward immigration, but would be interrupted by power failures or bad migration of S. furcifera is mainly driven by monsoon currents weather (e.g., strong wind and precipitation), as well as being una- (monsoons from the Pacific and Indian oceans) with the following ble to track demographic change as it only collects macropterous two forms: 1) long-range migration in East and South China where adults. Although ovary examination can partly identify outbreak the terrain is flat with less hills (Zhai 2011, Zhao et al. 2014) and sources in a few previously reported cases, it is on one hand too 2) short-range migration from the south to adjacent north in West sophisticated for most rural plant protection administrations to China where the terrain is very complex, featuring high-altitude apply, and on the other hand, it has only been reported from areas © The Author(s) 2019. Published by Oxford University Press on behalf of Entomological Society of America. This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/ 1 licenses/by-nc/4.0/), which permits non-commercial re-use, distribution, and reproduction in any medium, provided the original work is properly cited. For commercial re-use, please contact [email protected] 2 Journal of Insect Science, 2019, Vol. 19, No. 1 without overwintering populations (Lu et al. 2011, Chen et al. 2012, (23°38′N, 101°29′E, 449 m a.s.l.; Fig. 1); one of the areas with Zheng et al. 2014a, Ma et al. 2017). Hence, developing a monitoring severe outbreaks of S. furcifera during the past decade in Yunnan. method to compensate the existing measures would be necessary in Early-season rice and mid-season rice of a local variety ‘Yi Xiang the monitoring and forecasting of S. furcifera in China. II’ was grown continuously in this paddy, which was left vacant in Forecast and prevention methods for different outbreak sources winter months from December to the following February. Several and migration patterns should be differentiated in the light of ac- independent surveys have confirmed the existence of a local (over- tive prevention and control strategy. When a local or overwintering wintering) population on the ratooning rice in vacant paddies in population forms an early outbreak source, management of winter winter, and those due to immigrants in early- and mid-season rice paddies, and ratooning rice should be prioritized, followed by regular (Liu et al. 1991; Dou et al. 2012; Hu et al. 2015a,b). The experimen- monitoring and management measures. When the first and heaviest tal area was located at the center of this paddy, with a size of 200 outbreak sources usually come from immigrants, regular monitoring m2. No pesticides and herbicides were used throughout the exper- and preimmigration management should be taken equally (Hu 2013; iment, whereas regular managements such as water and fertilizers Hu et al. 2014, 2017). Hence, accurate identification of outbreak were applied as usual. sources and migration patterns of S. furcifera is crucial to formulate highly efficient prevention and control strategies. Experimental Devices The current study aimed to explore a new feasible survey method to The experimental device was a cubic cage, with a dimension of 2 × identify the source composition of a population of S. furcifera by setting 2 × 3 m. The frame of the cage was made of bamboo and nylon rope, up field cages to separate the population into two parts (inside and out- and the ceiling and four walls were covered with US-80 standard side the cages). After separation, both populations continue on their own nylon mesh (mesh opening 180 μm). The cage walls not only pre- demographic courses, but only the population outside the field cages is vented small nymphs of S. furcifera from entering or escaping but able to receive immigrants when migration occurs. The key purpose is also avoided significant ambient temperature and humidity differ- to distinguish immigrants from the mixed population composed of local ence by allowing ventilation through cage walls and ceiling. A zipper and migratory populations, as well as to obtain the scale and time of door was fixed to a 2 × 2 m wall for the investigator to enter and exit. migration. By setting up field cages, using periodic surveys, and statistical Three of such cages were installed at 10-m intervals into the comparisons of population densities, the current study has identified the paddy soil with four underground stands (40 cm each) and were source composition of S. furcifera. The methods and findings of this case reinforced against wind using nylon ropes at four apices (Fig. 2A). study would provide an example for effective monitoring and forecast Three equally sized (6 m2 each) rectangular areas without cages were of S. furcifera, as well as some clues for finally elucidating the migration also set at 10 m intervals next to the cages as controls (Fig. 2B; Supp pattern and outbreak mechanisms of S. furcifera in South China. Fig. 1 [online only]). The cages were set up 3 days before each starting date. Prior Materials and Methods to installation of the cages, 10 plots in the paddy were randomly selected to survey the population density of S. furcifera to avoid Field Site installing the cages in sites with obvious spatial density bias. After The field site of the current study was a rice paddy near the tropi- installation, walls with zippers were rolled up to leave them wide cal dry-hot Red-River Valley in Yuanjiang County, Yunnan, China open until the starting date. This ‘open door’ period allows the Fig. 1. Position of the field site and study area in Yunnan showing geographic topography and relevance with bordering countries and provinces Journal of Insect Science, 2019, Vol. 19, No. 1 3 S. furcifera population as well as its natural enemies (e.g., predators and beaten 10 times to shake the planthoppers off into a white plate and parasitoids) on both sides of each cage to interchange, in order (33 × 45 cm). The number of younger nymphs (YN, instars I–III), the to restore spatial density of S.