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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 （125） 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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Larval diet affects development and reproduction of East Asian strain of the fall armyworm, Spodoptera frugiperda

HE Li-mei, WANG Teng-li, CHEN Yu-chao, GE Shi-shuai, Kris A. G. WYCKHUYS, WU Kong-ming

2021, 20 (3): 736-744. DOI: 10.1016/S2095-3119(19)62879-0

Abstract （131） PDF in ScienceDirect

In December 11, 2018, the fall armyworm (FAW), Spodoptera frugiperda invaded China and has since impacted local maize, sorghum and other crops. Here, we draw on laboratory experiments to show how different host crops (i.e., maize, sorghum, wheat and rice) and artificial diet affect larval growth and adult reproduction of one local FAW strain. Larval diet affected development duration, pupation rate, survival and emergence rate of pupae, and S. frugiperda adult fecundity. FAW attained the slowest larval development (19.4 days) on sorghum and the fastest (14.1 days) on artificial diet, with larvae attaining 99.6% survival on the latter food item. On rice, FAW larvae attained survival rate of 0.4% and were unable to pupate successfully. Pupation rate and pupal survival varied substantially between artificial diet and live plantlets at different phenological stages. Pupal weight was the highest (0.26 g) on artificial diet and the lowest (0.14 g) on sorghum, while FAW females reached the highest fecundity (699.7 eggs/female) on 2-leaf stage maize. Egg hatching rate equaled 93.6% on 4- or 5-leaf stage maize and 36.6% on artificial diet. FAW intrinsic rate of natural increase and the finite rate of increase varied between larval diets, reflecting how young maize leaves are the most suitable diet. Our findings can help to refine laboratory rearing protocols, devise population forecasting models or guide the deployment of ‘area-wide’ integrated pest management (IPM) modules in FAW-invaded areas of China and other Asian countries.

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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 （94） 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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Adult nutrition affects reproduction and flight performance of the invasive fall armyworm, Spodoptera frugiperda in China

HE Li-mei, JIANG Shan, CHEN Yu-chao, Kris A. G. WYCKHUYS, GE Shi-shuai, HE Wei, GAO Xi-wu, WU Kong-ming

2021, 20 (3): 715-726. DOI: 10.1016/S2095-3119(20)63198-7

Abstract （78） PDF in ScienceDirect

Floral resources, such as carbohydrate-rich nectar or pollen, can bolster fitness and raise reproductive output of adult lepidopterans. Here, we used laboratory experiments to assess how those plant-derived foods impact adult fecundity, reproductive physiology and flight performance of an invasive strain of the fall armyworm, Spodoptera frugiperda (FAW; Lepidoptera: Noctuidae) in China. More specifically, supplementary feeding on bee pollen and honey enhanced FAW flight duration, testis size, ovarian development, longevity and adult fecundity. FAW adults attained the longest pre-oviposition (10.8 days) and oviposition period (6.8 days) and longevity (19.2 days) on 5% acacia honey. Upon access to 2.5% acacia honey and 2.5‰ pine pollen, S. frugiperda attained the highest mating rate (79.7%), fecundity (644.9 eggs/female) and egg hatching rate (82.3%). Feeding on honey further delayed decay of male testes, while ovarian development was enhanced when female moths were allowed access to 2.5% honey and 2.5‰ pine pollen. Upon feeding on 5% honey solution, S. frugiperda engaged in flight over the longest duration (9.5 h), distance (29.9 km) and speed (3.1 km h^–1). Honey had a comparatively greater effect on the above parameters than pollen. Our findings help decipher FAW invasion patterns and population dynamics, facilitate the development of nutritional attractants, and contribute to integrated pest management of this newly-invasive pest in eastern Asia.

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Laboratory-based flight performance of the fall armyworm, Spodoptera frugiperda

GE Shi-shuai, HE Li-mei, HE Wei, YAN Ran, Kris A. G. WYCKHUYS, WU Kong-ming

2021, 20 (3): 707-714. DOI: 10.1016/S2095-3119(20)63166-5

Abstract （79） PDF in ScienceDirect

In late 2018, the fall armyworm (FAW) Spodoptera frugiperda Smith (Lepidoptera: Noctuidae) made its arrival in China and its populations have since proliferated across most of eastern Asia. While S. frugiperda exhibits a considerable dispersal capacity and engages in long-distance migration, there’s only scant information on the species’ flight capability. Here, we empirically assessed S. frugiperda flight activity under varying climatic conditions using a flight mill. More specifically, under laboratory conditions, FAW exhibited superior flight performance at 20–25°C and 60–90% relative humidity (RH). When quantifying flight performance over five consecutive nights (i.e., 10 h/night), all flight parameters initially increased and then gradually dropped and FAW adults attained a total flight distance, duration and velocity equal to 63.73 km (48.42–94.12 km) (median, quartile range), 24.12 h (20.87–27.73 h) and 2.73 km h^–1 (2.13–3.33 km h^–1), respectively. Our work constitutes a first comprehensive assessment of S. frugiperda flight performance and provides baseline information for future efforts to forecast spatiotemporal changes in its geographical distribution, movement patterns and invasion trajectories. Such can ultimately permit a timely and targeted deployment of area-wide pest management measures against this newly-invasive pest in China and across eastern Asia.

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