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Accurate recognition of the reproductive development status and prediction of oviposition fecundity in Spodoptera frugiperda (Lepidoptera: Noctuidae) based on computer vision

LÜ Chun-yang, GE Shi-shuai, HE Wei, ZHANG Hao-wen, YANG Xian-ming, CHU Bo, WU Kong-ming

2023, 22 (7): 2173-2187. DOI: 10.1016/j.jia.2022.12.003

Abstract （188） PDF in ScienceDirect

Spodoptera frugiperda (Lepidoptera: Noctuidae) is an important migratory agricultural pest worldwide, which has invaded many countries in the Old World since 2016 and now poses a serious threat to world food security. The present monitoring and early warning strategies for the fall army worm (FAW) mainly focus on adult population density, but lack an information technology platform for precisely forecasting the reproductive dynamics of the adults. In this study, to identify the developmental status of the adults, we first utilized female ovarian images to extract and screen five features combined with the support vector machine (SVM) classifier and employed male testes images to obtain the testis circular features. Then, we established models for the relationship between oviposition dynamics and the developmental time of adult reproductive organs using laboratory tests. The results show that the accuracy of female ovary development stage determination reached 91%. The mean standard error (MSE) between the actual and predicted values of the ovarian developmental time was 0.2431, and the mean error rate between the actual and predicted values of the daily oviposition quantity was 12.38%. The error rate for the recognition of testis diameter was 3.25%, and the predicted and actual values of the testis developmental time in males had an MSE of 0.7734. A WeChat applet for identifying the reproductive developmental state and predicting reproduction of S. frugiperda was developed by integrating the above research results, and it is now available for use by anyone involved in plant protection. This study developed an automated method for accurately forecasting the reproductive dynamics of S. frugiperda populations, which can be helpful for the construction of a population monitoring and early warning system for use by both professional experts and local people at the county level.

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Two-way predation between immature stages of the hoverfly Eupeodes corollae and the invasive fall armyworm (Spodoptera frugiperda J. E. Smith)

LI Hui, JIANG Shan-shan, ZHANG Hao-wen, GENG Ting, Kris A. G. WYCKHUYS, WU Kong-ming

2021, 20 (3): 829-839. DOI: 10.1016/S2095-3119(20)63291-9

Abstract （120） PDF in ScienceDirect

Since its 2018 invasion of eastern Asia, the fall armyworm Spodoptera frugiperda (Lepidoptera: Noctuidae) has become a key pest in local maize production. Though pesticides have been widely used to mitigate the initial S. frugiperda attack, biological control is receiving ample attention as a desirable, environmentally-sound alternative to chemical control. Hoverflies (Diptera: Syrphidae) are abundant natural enemies in Chinese maize fields and have been observed to consume S. frugiperda larvae. In this study, we use laboratory assays to study the two-way interaction between immature stages of S. frugiperda and the endemic syrphid Eupeodes corollae. To mimic natural conditions, assays were performed in the presence of fresh maize leaves. Those 2nd or 3rd instar larvae of E. corollae preyed on 1st and 2nd instar S. frugiperda larvae with a Holling type III response, consuming a respective theoretical maximum of 43.48 and 83.33 larvae over a 24-h period. Conversely, once S. frugiperda larvae reached 3rd instar, they exhibited aggressive behavior and equally preyed on syrphid larvae with a Holling type III response. Those 5th and 6th instar larvae of S. frugiperda consumed a respective 16.39–19.23, 6.02–19.61 and 6.76–8.26 of 1st, 2nd and 3rd instar E. corollae larvae per day. Though our results await field-level validation, S. frugiperda agonistic (i.e., defensive) and consumptive behavior towards resident natural enemies such as E. corollae possibly degrades biotic resistance and raises its invasion potential. Our findings shine new light on the interaction between lepidopteran herbivores and their natural enemies, and can help advance the development of conservation biological control and other integrated pest management (IPM) strategies against S. frugiperda in China and abroad.

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Population occurrence of the fall armyworm, Spodoptera frugiperda (Lepidoptera: Noctuidae), in the winter season of China

YANG Xian-ming, SONG Yi-fei, SUN Xiao-xu, SHEN Xiu-jing, WU Qiu-lin, ZHANG Hao-wen, ZHANG Dan-dan, ZHAO Sheng-yuan, LIANG Ge-mei, WU Kong-ming

2021, 20 (3): 772-782. DOI: 10.1016/S2095-3119(20)63292-0

Abstract （106） PDF in ScienceDirect

Fall armyworm (FAW), Spodoptera frugiperda (J.E. Smith), has become an important pest in Chinese agricultural systems since its invasion on 11 December 2018. After its establishment, FAW months in the year-round breeding region have become the main source population migrating to other areas in China. Field investigations were conducted in tropical and subtropical regions to improve understanding of its year-round breeding area in China. The results showed that FAW larval density was significantly correlated with the seasonal temperature of the location surveyed. The FAW larvae maintained a high density in the tropical area and were frequently found in sites of the south subtropical region, but were absent from the north subtropical region and the northern part of the central subtropical region. These results indicated that FAW can reproduce annually in the tropical and south subtropical regions of China, including Hainan, Taiwan and the southern area of Fujian, Guangdong, Guangxi, Guizhou, and Yunnan. Hence, great effort should be made to monitor and control FAW in the year-round breeding region to suppress the population density of this area and to reduce migration of moths into northern parts of China. This study clarifies the occurrence area of the pest in winter in China and provides much valuable information for its population forecasting and management.

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Flight activity promotes reproductive processes in the fall armyworm, Spodoptera frugiperda

GE Shi-shuai, HE Wei, HE Li-mei, YAN Ran, ZHANG Hao-wen, WU Kong-ming

2021, 20 (3): 727-735. DOI: 10.1016/S2095-3119(20)63204-X

Abstract （150） PDF in ScienceDirect

The fall armyworm (FAW), Spodoptera frugiperda (Lepidoptera: Noctuidae), has invaded many countries in Africa and Asia since 2016, posing a major threat to world food security. Long-distance migration and strong reproductive ability form the biological basis of its rapid population expansion, but the relationship between the flight and reproduction of FAW has not been studied in depth. Here, an empirical assessment of this relationship in an invasive FAW population in China found that 1–3-day-old adults which had undergone 10-h tethered flights had a significantly shorter pre-oviposition period and greater oviposition synchronization, but did not show any differences in fecundity, oviposition period, mating percentage or other reproductive variables. Further studies on moths after 1.25–15-h tethered flights indicated that the reproductive process of adults could be fully triggered by flight activity longer than 2.5 h. Dissection of the reproductive organs also showed that tethered flight promoted ovarian and testicular development of FAW. These results show that appropriate moth flight activity significantly speeds up the reproductive process of FAW, which increases our knowledge on its migratory biology in relation to regional outbreaks.

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Spread of invasive migratory pest Spodoptera frugiperda and management practices throughout China

ZHOU Yan, WU Qiu-lin, ZHANG Hao-wen, WU Kong-ming

2021, 20 (3): 637-645. DOI: 10.1016/S2095-3119(21)63621-3

Abstract （164） PDF in ScienceDirect

The fall armyworm (FAW), Spodoptera frugiperda (J. E. Smith) (Lepidoptera: Noctuidae), a notorious migratory pest native to tropical and subtropical America, invaded China in December 2018, then spread through 26 provinces (autonomous regions, municipalities) in 2019 and 27 in 2020, damaging 1.125 and 1.278 million hectares of crops, respectively. Maize was the most severely affected crop, although wheat and other plants were also ruined. Considering the biological characteristics, incidence regularity and migration patterns of the FAW populations, Chinese government implemented a regional control strategy and divided the areas infested with FAW into the annual breeding grounds in Southwest and South China, the transitional migration area in Jiangnan and Jianghuai and the key preventive area in the Huang-Huai-Hai region and North China. The National Agro-Tech Extension and Service Center constructed “the National Information Platform for the Prevention and Control of the Fall Armyworm” at the county level, which would entail people reporting and mapping the spread of fall armyworm. According to forecasting information, millions of extension workers and small-scale growers in entire country were rallied by local governments to fight the pest through comprehensive control tactics including chemical, physical, biological and ecological measures. Thanks to the joint prevention and control, the final loss of crops infested was controlled within 5% of the total in 2019 and 2020. This review also gives a discussion on existing problems and future management scenarios.

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