High risk of the fall armyworm invading Japan and the Korean Peninsula via overseas migration

The fall armyworm, Spodoptera frugiperda (J.E. Smith), is an invasive pest species in the Old World. This species is originally native to the Americas. Since 2016, S. frugiperda has spread widely and rapidly throughout Africa, the Middle East, India, Southeast Asia and, most recently, to southern China. By May 2019, S. frugiperda had appeared in 13 provinces in southern China and will spread further into northern China. It is highly likely that S. frugiperda will enter Japan and Korea via overseas migrations as have many other migratory pests. To evaluate the risk of S. frugiperda invasion in Japan and the Korean Peninsula, we modelled the rate of expansion and future potential migratory range of the insect by a trajectory analytical approach using the flight behaviour of S. frugiperda and meteorological data of the past five years (2014–2018). If S. frugiperda can fly for up to 36 continuous hours over water, then our results predict migration from southern and eastern China into Japan and Korea. Most likely, Japan would be invaded from Fujian and Zhejiang in 1 June–15 July, and Kyushu, Shikoku and southwestern Honshu could face the highest risk of S. frugiperda invasion. Korea would most likely be reached by S. frugiperda from northern Zhejiang, Jiangsu, Anhui and Shandong in 1 June–15 July and later. Our results indicated a very high risk that S. frugiperda would annually invade Japan and the Korean Peninsula and cause a possible significant decrease in agricultural productivity.     

草地贪夜蛾综合防控技术研究进展

草地贪夜蛾是世界重大入侵性害虫,我国于2019年初发现草地贪夜蛾大面积危害西南地区玉米、高粱、甘蔗等多种作物,随后迅速扩散至主要玉米产区,严重威胁和影响我国粮食安全。国内研究人员已开展了大量关于草地贪夜蛾监测预警与防控技术的研究,在其种群发生规律监测、迁飞路径研判、化学防治、生物防治、物理防治等方面取得了系列进展,基本明确了草地贪夜蛾在我国西南、江南江淮、北方各地区的发生与危害规律,建立了一套草地贪夜蛾综合防控技术体系,有效阻断了其大面积扩散危害。本文综述了2019—2022年间国内草地贪夜蛾防控技术的研究进展,以期为开发草地贪夜蛾综合防控技术提供参考。     

基于集合模型的草地贪夜蛾的潜在分布预测

[目的]探讨世界范围和我国草地贪夜蛾对玉米等作物的危害.[方法]采用生态位模型集合预测方案,结合基于中分辨率成像光谱仪(MODIS)的玉米种植密度模拟,对世界范围和我国草地贪夜蛾潜在分布进行了分析.[结果]世界范围内玉米的密集种植区已完全被草地贪夜蛾的潜在分布区所覆盖,这些适生区内的玉米受到草地贪夜蛾的威胁,需重点防控...     

利用mtCOI PCR-RFLP技术鉴别草地贪夜蛾与其他3种形态相近昆虫

【目的】田间调查发现草地贪夜蛾与甜菜夜蛾、斜纹夜蛾、粘虫常混合发生,传统的形态学鉴定方法不能快速鉴别出该虫,当前亟需快速鉴别该虫的方法。【方法】本研究分析了草地贪夜蛾与甜菜夜蛾、斜纹夜蛾、粘虫mtCOI基因序列的酶切位点,根据目的片段设计上游引物并进行PCR-RFLP验证。【结果】草地贪夜蛾个体在mtCOI片段的556~561 bp处均存在Sbf I内切酶酶切位点,斜纹夜蛾、甜菜夜蛾、粘虫均无Sbf I酶切位点。草地贪夜蛾PCR产物经过Sbf I内切酶酶切,可出现420 bp左右的特征带,斜纹夜蛾、甜菜夜蛾、粘虫种群均不能被Sbf I内切酶酶切。【结论】基于新设计引物扩增的mtCOI片段的PCR-RFLP方法可有效鉴别草地贪夜蛾与其他3个形态相近昆虫,研究结果为草地贪夜蛾的快速鉴别提供了方法。     

Detection of ryanodine receptor target-site mutations in diamide insecticide-resistant Spodoptera frugiperda in China

Spodoptera frugiperda (Lepidoptera: Noctuidae) is a widely distributed pest of corn. Since it invaded China in 2018, it has caused serious damage to local corn production. Chlorantraniliprole, an anthranilic diamide insecticide, has been widely used to control lepidopteran pests. Tetrachloropyramid is a new allosteric modulator insecticide developed based on chlorantraniliprole, so it has a similar mechanism and insecticidal effect. In this study, we investigated resistance levels to chlorantraniliprole and tetrachloropyramid in S. frugiperda from 13 populations in China. Among the populations tested, the relative highest resistance to chlorantraniliprole occurred in the Guangzhou population, and the most susceptible to chlorantraniliprole was found in the Wuhan population. The lethal dosage LD₅₀ value of the Guangzhou population against chlorantraniliprole was 27.8-fold higher than that of the Wuhan population. Minimal differences were observed among S. frugiperda populations in terms of sensitivity to tetrachloropyramid. Heterozygous mutations at the I4734 site of the ryanodine receptor (RyR) were found, while no mutations were found in the G4891 site. The mutations were detected in only two of the 786 individuals analyzed, one from the Qinzhou population and other from the Anshun population (frequency below 2% in both cases). There were no significant differences in the expression levels of RyR between Guangzhou and Wuhan populations. In summary, our results indicate that: (i) S. frugiperda has low resistance levels to diamide insecticides in China; and (ii) the differences in relative resistance among the 13 populations analyzed are not caused by the mutations in RyR or the expression of RyR.     

Functional characterization of sex pheromone receptors in Spodoptera frugiperda,S. exigua,and S. litura moths

Moths possess an extremely sensitive and diverse sex pheromone processing system, in which pheromone receptors (PRs) are essential to ensure communication between mating partners. Functional properties of some PRs are conserved among species, which is important for reproduction. However, functional differentiation has occurred in some homologous PR genes, which may drive species divergence. Here, using genome analysis, 17 PR genes were identified from Spodoptera frugiperda, S. exigua, and S. litura, which belong to 6 homologous groups (odorant receptor [OR]6, 11, 13, 16, 56, and 62); of which 6 PR genes (OR6, OR11, OR13, OR16, OR56, and OR62) were identified in S. frugiperda and S. exigua, and 5 PR genes were identified in S. litura, excluding OR62. Using heterologous expression in Xenopus oocytes, we characterized the functions of PR orthologs including OR6, OR56, and OR62, which have not been clarified in previous studies. OR6 orthologs were specifically tuned to (Z,E)-9,12-tetradecadienyl acetate (Z9,E12-14:OAc), and OR62 orthologs were robustly tuned to Z7-12:OAc in S. frugiperda and S. exigua. The optimal ligand for OR56 was Z7-12:OAc in S. frugiperda, but responses were minimal in S. exigua and S. litura. In addition, SfruOR6 was male antennae-specific, whereas SfruOR56 and SfruOR62 were male antennae-biased. Our study further clarified the functional properties of PRs in 3 Spodoptera moth species, providing a comprehensive understanding of the mechanisms of intraspecific communication and interspecific isolation in Spodoptera.     

Baseline susceptibility of Helicoverpa armigera,Plutella xylostella,and Spodoptera frugiperda to the meta-diamide insecticide broflanilide

Broflanilide is a novel meta-diamide insecticide that acts as a γ-aminobutyric acid-gated chloride channel allosteric modulator. With its unique mode of action, broflanilide has no known cross-resistance with existing insecticides and is expected to be an effective tool for the management of insecticide resistance. Establishing the baseline susceptibility to this insecticide is an essential step for developing and implementing effective resistance management strategies. Here we evaluated the baseline susceptibility to broflanilide for 3 cosmopolitan lepidopteran pest species, Helicoverpa armigera, Plutella xylostella, and Spodoptera frugiperda. Broflanilide exhibited high activity against populations sampled in the major distribution range of these pests in China, with median lethal concentrations (LC₅₀) ranging between 0.209 and 0.684, 0.076 and 0.336, and 0.075 and 0.219 mg/L for H. armigera, P. xylostella, and S. frugiperda, respectively. Among-population variability in susceptibility to broflanilide was moderate for H. armigera (3.3-fold), P. xylostella (4.4-fold), and S. frugiperda (2.9-fold). The recommended diagnostic concentrations for H. armigera, P. xylostella, and S. frugiperda were 8, 4, and 2 mg/L, respectively. Little or no cross-resistance to broflanilide was detected in 3 diamide-resistant strains of P. xylostella and 1 spinosyns-resistant strain of S. frugiperda. Our results provide critical information for the development of effective resistance management programs to sustain efficacy of broflanilide against these key lepidopteran pests.     

Analysis of potential distribution of Spodoptera frugiperda in western China

Spodoptera frugiperda (J. E. Smith) (Lepidoptera: Noctuidae), a newly invaded pest that breaks out fast and severely, causes a serious threat to the national security of food production in China. In this study, the MaxEnt model was used to predict the potentially suitable distribution area of S. frugiperda in western China. The potential distribution of S. frugiperda was predicted using meteorological factors from the correlation analysis. According to the result, a satisfactory AUC value in the MaxEnt model indicates that the prediction model has good accuracy, which is sufficient for predicting the suitable distribution areas of S. frugiperda in western China. The prediction results show that the potential distribution risk of S. frugiperda is high in western Gansu, eastern Qinghai, Shaanxi, most regions of Ningxia, and part regions of Tibetan, and the most suitable areas for S. frugiperda in Xinjiang are Hami, Ili, Urumqi, Hotan and Aksu, and more than 60% of western China are suitable distribution areas for S. frugiperda. Western China is one of the main wheat and corn producing areas in China. Clarifying the potential geographical distribution of S. frugiperda in western China is essential for early warning as well as prevention and control.     

Noctuid migration in Texas within the nocturnal aeroecological boundary layer

Long-distance migration of adult corn earworm moths (Helicoverpazea), and several other noctuid moth species, facilitates seasonalexpansion of pest populations and consequent increased infestationsof agricultural crops on a continental scale in North America.Long-term field studies of population dynamics and migratoryflights of H. zea and fall armyworm (Spodoptera frugiperda)in the United States were evaluated using X-band radar observationsand profiles of atmospheric conditions. These studies identifiedcharacteristic patterns of migratory flight that are largelyassociated with vertical profiles of temperature and wind speed.Collective patterns of moth migrations were generally highlycorrelated with wind headings, but often at a significant angulardeviation. Preliminary analyses are presented between moth distributionsin the aerosphere estimated from discrete moth counts usingX-band radar and bulk reflectivity data from NEXRAD Dopplerradar. Identification of associations between atmospheric factorsand noctuid population dynamics and migratory flights will improvethe ability to predict infestations by pest species throughouttheir broad seasonal range expansion.     

Whole-genome sequencing to detect mutations associated with resistance to insecticides and Bt proteins in Spodoptera frugiperda

The fall armyworm (FAW), Spodoptera frugiperda, is a major pest native to the Americas that has recently invaded the Old World. Point mutations in the target-site proteins acetylcholinesterase-1 (ace-1), voltage-gated sodium channel (VGSC) and ryanodine receptor (RyR) have been identified in S. frugiperda as major resistance mechanisms to organophosphate, pyrethroid and diamide insecticides respectively. Mutations in the adenosine triphosphate-binding cassette transporter C2 gene (ABCC2) have also been identified to confer resistance to Cry1F protein. In this study, we applied a whole-genome sequencing (WGS) approach to identify point mutations in the target-site genes in 150 FAW individuals collected from China, Malawi, Uganda and Brazil. This approach revealed three amino acid substitutions (A201S, G227A and F290V) of S. frugiperda ace-1, which are known to be associated with organophosphate resistance. The Brazilian population had all three ace-1 point mutations and the 227A allele (mean frequency = 0.54) was the most common. Populations from China, Malawi and Uganda harbored two of the three ace-1 point mutations (A201S and F290V) with the 290V allele (0.47–0.58) as the dominant allele. Point mutations in VGSC (T929I, L932F and L1014F) and RyR (I4790M and G4946E) were not detected in any of the 150 individuals. A novel 12-bp insertion mutation in exon 15 of the ABCC2 gene was identified in some of the Brazilian individuals but absent in the invasive populations. Our results not only demonstrate robustness of the WGS-based genomic approach for detection of resistance mutations, but also provide insights for improvement of resistance management tactics in S. frugiperda.     

Resistance of the fall armyworm,Spodoptera frugiperda,to transgenic Bacillus thuringiensis Cry1F corn in the Americas: lessons and implications for Bt corn IRM in China

The fall armyworm, Spodoptera frugiperda (J.E. Smith), is a major target pest of Bt crops (e.g., corn, cotton, and soybean) in North and South America. This pest has recently invaded Africa and Asia including China and the invasion has placed a great threat to the food security in many countries of these two continents. Due to the extensive use of Bt crops, practical resistance of S. frugiperda to Cry1F corn (TC 1507) with field control problems has widely occurred in Puerto Rico, Brazil, Argentina, and the mainland United States. Analyzing data generated from decade-long studies showed that several factors might have contributed to the wide development of the resistance. These factors include (1) limited modes of action of Bt proteins used in Bt crops; (2) cross-resistance among Cry1 proteins; (3) use of nonhigh dose Bt crop traits; (4) that the resistance is complete on Bt corn plants; (5) abundant in initial Cry1F resistance alleles; and (6) lack of fitness costs/recessive fitness costs of the resistance. The long-term use of Bt crop technology in the Americas suggests that Bt corn can be an effective tool for controlling S. frugiperda in China. IRM programs for Bt corn in China should be as simple as possible to be easily adopted by small-scale growers. The following aspects may be considered in its Bt corn IRM programs: (1) use of only “high dose” traits for both S. frugiperda and stalk borers; (2) developing and implementing a combined resistance monitoring program; (3) use “gene pyramiding” as a primary IRM strategy; and (4) if possible, Bt corn may not be planted in the areas where S. frugiperda overwinters. Lessons and experience gained from the global long-term use of Bt crops should have values in improving IRM programs in the Americas, as well as for a sustainable use of Bt corn technology in China.     

Coconut leaf bioactivity toward generalist maize insect pests

Tropical plants are often more resistant to insects than temperate plants due to evolution of robust defenses to cope with a more constant insect threat. Coconut [Cocos nucifera L. (Arecaceae)] has very few chewing‐type leaf feeding insect pests and was tested for feeding suitability against two generalist leaf feeding caterpillar species, corn earworm, Helicoverpa zea (Boddie), and fall armyworm, Spodoptera frugiperda (J.E. Smith) (both Lepidoptera: Noctuidae). Feeding on leaf tissues from the most recently expanded leaves of a coconut variety caused significant mortality and reduced growth rates (as indicated by survivor weights) of S. frugiperda and H. zea compared to when they fed on leaves from a typical host, maize [Zea mays L. (Poaceae)], or the standard artificial diet. Proteins or other polymers did not appear to be responsible for the bioactivity noted against the caterpillars. Components responsible for activity were acetone extractable and separable by thin layer chromatography. Extracts from multiple areas of the thin layer chromatography (TLC) plates caused significant reductions in growth rates of S. frugiperda. The most bioactive TLC‐separated component, identified as pheophytin a, caused oxidative browning of test diets, suggesting that cytotoxicity of reactive oxygen species is a likely mode of action against H. zea and S. frugiperda.     

Sesquiterpene lactones of Vernonia — influence of glaucolide-A on the growth rate and survival of Lepidopterous larvae

Summary Sesquiterpene lactone glaucolide-A from Vernonia, incorporated in the rearing diets of five species of Lepidoptera, significantly reduced the rate of growth of larvae of the southern armyworm, Spodoptera eridania; fall armyworm, S. frugiperda; and yellowstriped armyworm, S. ornithogalli. Quantitative feeding tests demonstrated that decreased feeding levels and reduced growth resulted from ingestion of a sesquiterpene lactone. Ingestion of glaucolide-A increased the number of days to pupation in four of the species. In the southern armyworm, it significantly reduced pupal weight. Glaucolide-A decidedly reduced percentage of survival of southern and fall armyworms. Yellow woollybear, Diacrisia virginica, and cabbage looper, Trichoplusia ni, larvae were essentially uneffected by the ingestion of the sesquiterpene lactone. Sesquiterpene lactones adversely affect growth rate and survival of certain insects that feed upon plants containing them. They apparently function as defensive products, screening out a portion of the potential herbivores.Vernonieae: Compositae     

Morphological and immunohistochemical study of the midgut and fat body of Spodoptera frugiperda (J.E. Smith) (Lepidoptera: noctuidae) treated with essential oils of the genus Piper

ABSTRACT

Essential oils are a promising alternative to insecticides. We investigated the LD₅₀ of oils extracted from Piper corcovadensis, P. marginatum, and P. arboreum after 48 h topical contact with Spodoptera frugiperda larvae using morphometry, histochemistry and immunohistochemistry of the midgut and fat body. Chromatography revealed that E-caryophyllene was the principal compound common to the Piper species. The essential oils of P. corcovadensis, P. marginatum and P. arboreum caused deleterious changes in the midgut of S. frugiperda larvae. P. corcovadensis oil produced the lowest LD₅₀ and significant histopathological alterations including elongation of the columnar cells, formation of cytoplasmic protrusions, reduction in carbohydrate, increased apoptotic index and decreased cell proliferation. P. arboreum oil caused histopathological alterations similar to P. corcovadensis, but caused the highest rate of cell proliferation and increased regenerative cells, which indicated rapid regeneration of the epithelium. Our findings demonstrated the insecticidal potential of P. corcovadensis for control of S. frugiperda owing to the significant damage it inflicted on S. frugiperda midgut.     

Identification of Volicitin-related Compounds from the Regurgitant of Lepidopteran Caterpillars

Volicitin-related compounds were found in the oral secretion of the three noctuid species, Helicoverpa armigera, Mythimna separata and Spodoptera litura, and one sphingid species, Agrius convolvuli. Volicitin [N-(17-hydroxylinolenoyl)-L-glutamine], N-(17-hydroxy-linoleoyl)-glutamine, N-linolenoylglutamine and N-linoleoylglutamine were identified in the secretion from the noctuid larvae. In secretions from the sphingid larvae, N-linolenoylglutamine and N-linoleoylglutamine were the main components. Furthermore, there were significant differences in the amounts of the N-acylamino acid conjugates in the secretions from the three noctuid species. These results suggest that the proportion of volicitin-related compounds in the regurgitant was species-specific.     

Fitness costs of Cry1F resistance in fall armyworm,Spodoptera frugiperda

Transgenic corn, Zea mays L., expressing the Bacillus thuringiensis Berliner (Bt) protein Cry1F has been registered for Spodoptera frugiperda (J. E. Smith) control since 2003 in the USA. Unexpected damage to Cry1F corn was reported in 2006 in Puerto Rico, and Cry1F resistance in S. frugiperda from Puerto Rico was documented. The study of fitness costs associated with insect resistance to Bt insecticidal proteins is important for understanding resistance evolution and for evaluating resistance management practices used to mitigate resistance to transgenic corn. Currently, no studies have addressed the fitness costs associated with Cry1F resistance in S. frugiperda. In this study, susceptible and resistant strains with similar genetic background and their reciprocal crosses were used to estimate Cry1F resistance fitness costs. Comparisons between life‐history traits and population growth rates of homozygous susceptible, heterozygous and homozygous resistant S. frugiperda were used to determine whether the resistance is associated with fitness costs. Major fitness costs were not apparent in either heterozygotes or homozygous resistant insects. However, there was a slight indication of hybrid vigour in the heterozygotes. Additionally, two lines in which the frequency of the resistant alleles was fixed at 0.5 were followed for seven generations, after which the frequency of resistant alleles slightly decreased in both lines. The lack of strong fitness costs associated with Cry1F resistance in S. frugiperda indicates that initial allele frequencies may be higher than expected in field populations and will tend to remain stable in field populations in the absence of selection pressure (e.g. Puerto Rico).     

Rapid selection and characterization of Cry1F resistance in a Brazilian strain of fall armyworm

Transgenic maize (Zea mays L., Poaceae) event TC1507, producing the Cry1F protein of Bacillus thuringiensis Berliner, has been used for management of the fall armyworm, Spodoptera frugiperda (JE Smith) (Lepidoptera: Noctuidae), in Brazil since 2009. A strain of S. frugiperda, obtained from field collections of larvae in TC1507 maize in Minas Gerais state in 2010, was selected in the laboratory for resistance to Cry1F using leaves of TC1507 maize in two selection regimes. Continuous exposure of larvae to Cry1F was more effective than exposure for 6, 8, and 10 days in the selection of resistant S. frugiperda individuals. With only four generations of laboratory selection, a strain with high levels of resistance to Cry1F was obtained, as indicated by the survival of insects reared on leaves of TC1507 maize plants and by the more than 300‐fold resistance level measured in bioassays with the purified Cry1F protein. Importantly, reciprocal crosses between control and the Cry1F‐selected strains revealed that the resistance is autosomal and incompletely recessive, and the response obtained in the backcross of the F₁ generation with the resistant strain was consistent with simple monogenic inheritance. Additionally, there were no apparent fitness costs associated with resistance either for survival or larval growth on non‐Bt maize leaves. Our findings provide experimental evidence for rapid evolution of Cry1F resistance in S. frugiperda in the laboratory and further reinforce the potential of this species to evolve field resistance to the TC1507 maize as previously reported. The resistant strain isolated in this study provides an opportunity to estimate the resistance allele frequency in the field and to determine the biochemical and molecular basis of the resistance, which should provide further information to assist in the resistance management of S. frugiperda on transgenic maize producing B. thuringiensis proteins.     

Effect of cold acclimation and rapid cold-hardening on the survival of Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae) under cold stress

Spodoptera frugiperda is a highly invasive pest species that recently invaded Africa and Asia causing severe economic losses, primarily related to corn and rice crops. Temperature is one of the most important environmental factors that influence the invasion of pests into new habitats. However, little is known regarding the thermal tolerance characteristics of invasive S. frugiperda. Thus, we investigated the response of four developmental stages of S. frugiperda (i.e., eggs, third and sixth instar larvae, and pupae) to cold acclimation (CA) and rapid cold-hardening (RCH). All individuals suffered high mortality with 24-h temperature treatments at <?5°C and >35 °C. The CA treatment significantly increased the survival rate of the eggs and third instar larvae, although it did not affect the sixth instar larvae and it decreased the pupation rate. The RCH treatment at 5 °C for 5 h or 2 °C for 2 h increased the cold tolerance capabilities of the third and sixth instar larvae, respectively. Thus, the larval stage appears to be crucial for the cold tolerance of S. frugiperda. Our findings improve the current understanding of the cold tolerance characteristics of S. frugiperda and indicate its potential for survival in the newly invaded temperate regions of Asia.