Seasonal Pattern of Spodoptera litura (Lepidoptera: Noctuidae) Migration Across the Bohai Strait in Northern China

Migration Activity of Spodoptera litura (Lepidoptera: Noctuidae) between China and the South-Southeast Asian Region

The common cutworm, Spodoptera litura (F.), feeds on a wide variety of food and cash crops and is one of the most widespread and destructive agricultural pests worldwide. Migration is the biological basis of its regional population outbreaks but the seasonal movement of this pest between east and south Asia regions remains unknown. In this study, searchlight traps were used to monitor the seasonal migration of S. litura from 2019 to 2023 in Ruili City (Yunnan, China), located along the insect migratory route between China and the south Asia region. The results showed that migratory activity could occur throughout the year, with the main periods found in spring (April-May) and autumn (October-December). The ovarian development and mating status of the trapped females indicated that most individuals were in the middle or late stages of migration and that Ruili City was located in the transit area of the long-distance migration of the pest. In the migration trajectory simulation, populations of S. litura moved from northeast India, Bangladesh, and northern Myanmar to southwestern China along the southern margin of the Himalayas in spring and returned to the south Asia region in autumn. Our findings clarify the seasonal migration patterns of S. litura in China and South Asia and facilitate the development of regional cross-border monitoring and management systems for this pest.

Performance and preference of larval parasitoid, Microplitis pallidipes (Hymenoptera: Braconidae), on 2 Spodoptera pest species

Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae) and Spodoptera litura (Fabricius) are the main pests on corn (Poaceae: Gramineae). The performance of the larval wasp, Microplitis pallidipes Szépligeti (Hymenoptera: Braconidae), was reported on S. frugiperda and S. litura. In this study, we evaluated host selectivity, constructed an age-stage, 2-sex life table, and assessed the pest control potential of M. pallidipes against these 2 pests under laboratory conditions. In a 2-choice host preference experiment, M. pallidipes exhibited a stronger preference for S. frugiperda over S. litura and a distinct preference for second instars. We also investigated the parasitism of females that were either unfed or fed with 10% honey-water solution under different host densities and found that the highest parasitism rate was observed when M. pallidipes were fed with honey-water solution on the first day after mating and a presented female wasp:host ratio of 1:90. In a nonselective assay, M. pallidipes successfully completed a full generation on both hosts. However, the parasitoids exhibited higher fitness and population growth potential when reared on S. frugiperda, with a net reproductive rate (R0) of 24.24, an intrinsic rate of increase (r) of 0.20 per day, a finite rate of increase (λ) of 1.23 per day, and a mean generation time (T) of 15.69 days. This study elucidates the performance of M. pallidipes on 2 Spodoptera host species and offers insights into its biological control potential on lepidopteran pests.

Population dynamics and seasonal migration patterns of Spodoptera exigua in northern China based on 11 years of monitoring data

Background

The beet armyworm, Spodoptera exigua (Hübner), is an important agricultural pest worldwide that has caused serious economic losses in the main crop-producing areas of China. To effectively monitor and control this pest, it is crucial to investigate its population dynamics and seasonal migration patterns in northern China.

Methods

In this study, we monitored the population dynamics of S. exigua using sex pheromone traps in Shenyang, Liaoning Province from 2012 to 2022, combining these data with amigration trajectory simulation approach and synoptic weather analysis.

Results

There were significant interannual and seasonal variations in the capture number of S. exigua, and the total number of S. exigua exceeded 2,000 individuals in 2018 and 2020. The highest and lowest numbers of S. exigua were trapped in September and May, accounting for 34.65% ± 6.81% and 0.11% ± 0.04% of the annual totals, respectively. The average occurrence period was 140.9 ± 9.34 days during 2012-2022. In addition, the biomass of S. exigua also increased significantly during these years. The simulated seasonal migration trajectories also revealed varying source regions in different months, primarily originated from Northeast China and East China. These unique insights into the migration patterns of S. exigua will contribute to a deeper understanding of its occurrence in northern China and provide a theoretical basis for regional monitoring, early warning, and the development of effective management strategies for long-range migratory pests.

Eco-friendly approaches of zinc oxide and silver nitrate nanoparticles along with plant extracts against Spodoptera litura (Fabricius) under laboratory conditions

The tobacco cutworm (Spodoptera litura) is a widespread pest that inflicts severe damage on various crops, including cotton, tobacco, and vegetables, with a particular preference for solanaceous plants. Traditional control methods often rely heavily on synthetic insecticides, leading to adverse effects on the environment, human health, and the development of insecticide resistance. In light of these challenges, this study explores the potential of nanotechnology as an innovative and sustainable approach to combat this notorious pest. Bioassays were conducted using laboratory-reared 3rd instar S. litura larvae. Eight different plant extracts coated with zinc oxide and silver nitrate nanoparticles were tested, with concentrations in both distilled water and ethanol at 3, 5, and 7 ml. Data were collected at 24, 48, and 72-h intervals. The results revealed that the highest larval mortality, reaching 98%, was observed in the group treated with silver nitrate nanoparticles derived from Cymbopogon citratus. In comparison, the group treated with zinc oxide nanoparticles dissolved in ethanol exhibited a larval mortality rate of 90%. Ethanol is a polar solvent that is widely used in the synthesis of nanocomposites. It is capable of forming strong hydrogen bonds with oxygen atoms, making it a good dispersant for zinc oxide nanoparticles. Additionally, ethanol has a low boiling point and a non-toxic nature, which makes it a safe and effective option for the dispersion of nanoparticles. Notably, the study concluded that silver nanoparticles combined with ethanol exhibited prolonged and more potent toxic effects against S. litura when compared to zinc oxide nanoparticles. Overall, this research underscores the potential of nanotechnology as a valuable component of Integrated Pest Management (IPM) strategies. By integrating nanotechnology into pest management practices, we can promote sustainable and environmentally friendly approaches that benefit both farmers and the ecosystem.

Comigration and interactions between two species of rice planthopper (Laodelphax striatellus and Sogatella furcifera) and natural enemies in eastern Asia

BACKGROUND

Natural enemies are important in pest control. However, control by natural enemies is hindered by the migration of rice planthoppers. Therefore, comigration and interactions between Laodelphax striatellus (Fallén) and Sogatella furcifera (Horváth) and five predator species, Chrysoperla sinica Tjeder, Harmonia axyridis (Pallas), Episyrphus balteatus, Syrphus corollae (Fab.) and Chrysopa pallens (Rambur) in eastern Asia were investigated.

RESULTS

From 2012 to 2021, the migration patterns of two rice planthoppers and five natural enemy species were monitored by suction trapping on Beihuang Island, Shandong Province, China. Both planthoppers and the five natural enemies regularly comigrated from late April to late October each year. There were significant interannual and seasonal differences in the numbers of two rice planthoppers migrating across this island. Simulated seasonal migration trajectories indicated different source areas for the two rice planthoppers, which mainly originated in northeast, north and east China. The biomass of planthoppers was significantly positively correlated with that of the ladybug H. axyridis in all migration periods, and significant differences in the ratio of rice planthoppers to natural enemies among months. A time-lag effect between seasons was obtained when natural enemies and pests comigrated.

CONCLUSION

Migration was coordinated between rice planthoppers and natural enemies in East Asia. When natural enemies and rice planthoppers comigrated, time lags between seasons were observed. The unique insights into the migration patterns will help to increase understanding of the occurrence of rice planthoppers in eastern Asia and provide an important theoretical basis for regional monitoring and management of rice planthoppers. © 2023 Society of Chemical Industry.

Extremely high relative growth rate makes the cabbage white, Pieris rapae, a global pest with highly abundant and migratory nature

The small cabbage white butterfly, Pieris rapae, is an extraordinarily abundant migratory pest of cabbage that causes severe damage worldwide without known reasons. I here show that the average relative growth rate (RGR: the ratio of the daily increase of biomass to total biomass) of herbivore (Gh; an indicator of the growth speed of herbivore) of P. rapae on cabbage during the larval period is larger by far than those of all other insect-plant pairs tested. It exceeds 1.15 (/day),-meaning that the biomass more than doubles each day-compared to 0.1-0.7 for most insect-plant pairs, including that of Pieris melete, a sibling of P. rapae which never becomes a pest of cabbage. My data further showed the RGR in the larval stage (larval Gh), positively correlates with abundance and/or migratoriness of insect herbivores. These results together with my mathematical food web model suggest that the extraordinarily high larval Gh of P. rapae is the primary reason for its ubiquitously severe pest status accompanied with its abundance and migratoriness, and that the RGR of herbivores, Gh, characterizing the plant-herbivore interface at the bottom of the food webs is an important factor affecting whole ecosystems, including animal abundance, fauna size, plant damage levels, competitiveness among herbivorous species, determination of hostplant, invasiveness, and the evolution of animal traits involved in the so-called r/K strategy, such as migratoriness. Knowledge about Gh will be crucial to controlling pests and improving the negative effects of human activity on ecosystems including faunal decline (or defaunation).

A novel domain-duplicated SlitFAR3 gene involved in sex pheromone biosynthesis in Spodoptera litura

Fatty acyl reductases (FARs) are key enzymes that participate in sex pheromone biosynthesis by reducing fatty acids to fatty alcohols. Lepidoptera typically harbor numerous FAR gene family members. Although FAR genes are involved in the biosynthesis of sex pheromones in moths, the key FAR gene of Spodoptera litura remains unclear. In this work, we predicted 30 FAR genes from the S. litura genome and identified a domain duplication within gene SlitFAR3, which exhibited high and preferential expression in the sexually mature female pheromone glands (PGs) and a rhythmic expression pattern during the scotophase of sex pheromone production. The molecular docking of SlitFAR3, as predicted using a 3D model, revealed a co-factor NADPH binding cavity and 2 substrate binding cavities. Functional expression in yeast cells combined with comprehensive gas chromatography indicated that the SlitFAR3 gene could produce fatty alcohol products. This study is the first to focus on the special phenomenon of FAR domain duplication, which will advance our understanding of biosynthesis-related genes from the perspective of evolutionary biology.

Identification and Expression Profiles of Candidate Sex Pheromone Biosynthesis Genes by the Transcriptome Analysis of Sex Pheromone Glands in Spodoptera litura and Spodoptera exigua

Like many insects, females of the Noctuid moth Spodoptera litura and Spodoptera exigua release chemical signals to attract males from a long distance for successful mating. In this study, 98 and 86 genes related to the sex pheromone biosynthesis of S. litura and S. exigua were identified. The tissue expression profiles of highly expressed genes in sex pheromone glands (PGs) were further examined by real-time quantitative polymerase chain reaction. The results displayed that only SlitDes5 and SexiDes5 gene were specifically and significantly overexpressed in the PGs of S. litura and S. exigua. The functional study of SlitDes5 gene showed that RNA interference reduced its expression level by 49.42%. In addition, the content of the sex pheromones of S. litura, Z9E11-14:OAc, Z9E12-14:OAc, E11-14:OAc, and Z9-14:OAc, decreased by 41.98% on average. Our findings provide a basis for better understanding the key genes that affect the biosynthesis of sex pheromones and for determining potential gene targets for pest control strategies.

Larvicidal, growth inhibitory and biochemical effects of soil bacterium, Pseudomonas sp. EN4 against Spodoptera litura (Fab.) (Lepidoptera: Noctuidae)

BACKGROUND

Spodoptera litura (Fabricius) (Lepidoptera: Noctuidae) also known as tobacco caterpillar, is one of the most serious polyphagous pests that cause economic losses to a variety of commercially important agricultural crops. Over the past few years, many conventional insecticides have been used to control this pest. However, the indiscriminate use of these chemicals has led to development of insecticide resistant populations of S. litura in addition to harmful effects on environment. Due to these ill effects, the emphasis is being laid on alternative eco-friendly control measures. Microbial control is one of the important components of integrated pest management. Thus, in search for novel biocontrol agents, the current work was carried out with the aim to evaluate the insecticidal potential of soil bacteria against S. litura.

RESULTS

Among the tested soil bacterial isolates (EN1, EN2, AA5, EN4 and R1), maximum mortality (74%) was exhibited by Pseudomonas sp. (EN4). The larval mortality rate increased in a dose-dependent manner. Bacterial infection also significantly delayed the larval development, reduced adult emergence, and induced morphological deformities in adults of S. litura. Adverse effects were also detected on various nutritional parameters. The infected larvae showed a significant decrease in relative growth and consumption rate as well as efficiency of conversion of ingested and digested food to biomass. Histopathological studies indicated damage to the midgut epithelial layer of larvae due to the consumption of bacteria treated diet. The infected larvae also showed a significantly decreased level of various digestive enzymes. Furthermore, exposure to Pseudomonas sp. also caused DNA damage in the hemocytes of S. litura larvae.

CONCLUSION

Adverse effects of Pseudomonas sp. EN4 on various biological parameters of S. litura indicate that this soil bacterial strain may be used as an effective biocontrol agent against insect pests.

Functional differentiation of two general odorant-binding proteins to sex pheromones in Spodoptera frugiperda

A precise chemosensory system can help insects complete various important behavioral responses by accurately identifying different external odorants. Therefore, deeply understanding the mechanism of insect recognition of important odorants will help us develop efficient and environmentally-friendly behavioral inhibitors. Spodoptera frugiperda is a polyphagous pest that feeds on >350 different host plants worldwide and also harms maize production in China. However, the molecular mechanism of the first step for males to use odorant-binding proteins (OBPs) to recognize sex pheromones remains unclear. Here, we obtained 50 OBPs from the S. frugiperda genome, and the expression level of SfruGOBP1 in females was significantly higher than that in males, whereas SfruGOBP2 displayed male-biased expression. Fluorescence competitive binding assays showed that only SfruGOBP2 showed binding affinities for the four sex pheromones of female S. frugiperda. Subsequently, we identified some key amino acid residues that can participate in the interaction between SfruGOBP2 and sex pheromones using molecular docking and site-directed mutagenesis methods. These findings will help us explore the interaction mechanism between GOBPs and sex pheromones in moths, and provide important target genes for developing new mating inhibitors of S. frugiperda in the future.

Genetic Diversity and Fine-Scale Genetic Structure of Spodoptera litura Fabricius (Lepidoptera: Noctuidae) in Southern China Based on Microsatellite Markers

Population genetic structure is strongly affected by dispersal events, especially for migratory species. The investigation of population structure is therefore conducive to increasing our understanding of species dispersal. Spodoptera litura (Fabricius) (Lepidoptera: Noctuidae) is an important tobacco pest in China causing serious damage to multiple crops. In this study, we explore its dispersal dynamics by clarifying the fine-scale population genetics using 545 S. litura samples collected from tobacco plantations at 24 locations (mainly in Baise, Hechi, and Hezhou, Southern China). We analyzed the genetic diversity, genetic structure, and gene flow of these populations using seven microsatellite loci. Our results revealed high genetic diversity and low population genetic structure among S. litura. The genetic distance was uncorrelated with geographical distance, indicating the complete randomness of dispersal among the local populations. Our results suggest that the movement scope of contemporary S. litura might be much higher than the local-level spatial scale, which will provide a theoretical basis for pest management.

Two Odorant-Binding Proteins Involved in the Recognition of Sex Pheromones in Spodoptera litura Larvae

Usually, the recognition of sex pheromone signals is restricted to adult moths. Here, our behavioral assay showed that fourth-instar Spodoptera litura larvae are attracted to cabbage laced with minor sex pheromones Z9,E12-tetradecadienyl acetate (Z9,E12-14:Ac) or Z9-tetradecenyl acetate (Z9-14:Ac). Seven odorant-binding proteins (OBPs) were upregulated after exposure to Z9,E12-14:Ac, and one OBP was upregulated after exposure to Z9-14:Ac. Fluorescence competitive binding assays showed that GOBP2 and OBP7 bound to sex pheromones. RNAi treatment significantly downregulated GOBP2 and OBP7 mRNA expression by 70.37 and 63.27%, respectively. The siOBP-treated larvae were not attracted to Z9,E12-14:Ac or Z9-14:Ac, and the corresponding preference indices were significantly lower than those in siGFP-treated larvae. Therefore, we concluded that GOBP2 and OBP7 are involved in the attraction of S. litura larvae to food containing Z9,E12-14:Ac and Z9-14:Ac. These results provide an important basis for exploring the olfactory mechanisms underlying sex pheromone attraction in moth larvae.

Effect of X-ray irradiation on development, flight, and reproduction of Spodoptera litura

Spodoptera litura is an omnivorous pest that has spread globally. Because irradiation sterilization technology has a great potential for control of S. litura, the effect of 25–150 Gy doses of X-rays on pupal survival, flight and reproductive variables of adult moths were analyzed in this research. The X-ray irradiation with the dose of 25–150 Gy significantly affected the reproductive ability of females. Irradiating male pupae with 25–150 Gy doses of X-rays had no effect on mating, life span, or flight ability of adult moths, but significantly reduced survival and fecundity of their offspring, and the sterility rate of the F₁ generation was 52.65%–99.9%. The results of logistic curve fitting showed that the sterility impact was 84% at the most appropriate irradiation dose (71.26 Gy). The sterility control was 91% in an indoor mating competition experiment when the release ratio of irradiated males (75 Gy) to nonirradiated males reached 12.6:1. The effects of X-ray irradiation doses on biological variables of S. litura and the most effective release ratio determined here provide a theoretical foundation for using radiation sterilization technology to control S. litura.

Influence of seasonal migration on evolution of insecticide resistance in Plutella xylostella

The diamondback moth, Plutella xylostella (L.), is one of the most destructive migratory pest species of cruciferous vegetables worldwide and has developed resistance to most of the insecticides used for its control. The migration regularity, migratory behavior, and relationship between flight and reproduction of P. xylostella have been widely reported. However, the effect of migration on insecticide resistance in this pest is still unclear. In this study, the effect of migration on P. xylostella resistance to seven insecticides was investigated using populations across the Bohai Sea that were collected in the early and late seasons during 2017-2019. The bioassay results showed that the early season populations of P. xylostella from south China possessed much higher resistance to insecticides because of intensive insecticide application; alternatively, the late season populations migrated from northeast China, where the insecticides were only used occasionally, showed much lower insecticide resistance. The genome re-sequencing results revealed that, among the eight mutations involved in insecticide resistance, the frequencies of two acetylcholinesterase mutations (A298S and G324A) responsible for organophosphorus insecticide resistance were significantly decreased in the late season populations. The results indicated that P. xylostella migration between tropical and temperate regions significantly delayed the development of insecticide resistance. These findings illustrated the effect of regional migration on the evolution of insecticide resistance in P. xylostella, and provided foundational information for further research on the relationship between migration and insecticide resistance development in other insects.

Simulation of the Radar Cross Section of a Noctuid Moth

Electromagnetic modelling may be used as a tool for understanding the radar cross section (RCS) of volant animals. Here, we examine this emerging method in detail and delve deeper into the specifics of the modelling process for a single noctuid moth, with the hope of illuminating the importance of different aspects of the process by varying the morphometric and compositional properties of the model. This was accomplished by creating a high-fidelity three-dimensional insect model by micro-CT scanning a gold-palladium-coated insect. Electromagnetic simulations of the insect model were conducted by applying different morphological and compositional configurations using the WiPL-D Pro 3D Electromagnetic Solver. The simulation results show that high-resolution modelling of insects has advantages compared to the simple ellipsoidal models used in previous studies. We find that the inclusion of wings and separating the composition of the body, wings, and legs and antennae have an impact on the resulting RCS of the specimen. Such modifications to the RCS are missed when a prolate spheroid model is used and should not be ignored in future studies. Finally, this methodology has been shown to be useful in exploring the changes in the RCS that result from variations in specimen size. As such, utilising this methodology further for more species will improve the ability to quantitatively interpret aeroecological observations of weather surveillance radars and special-purpose entomological radars.

Insecticidal and growth inhibitory activity of gut microbes isolated from adults of Spodoptera litura (Fab.)

BACKGROUND

Spodoptera litura (Fab.) (Lepidoptera: Noctuidae) commonly known as tobacco caterpillar is a polyphagous pest that causes significant damage to many agricultural crops. The extensive use of chemical insecticides against S. litura has resulted in development of resistance. In order to find potential biocontrol agents, gut microbes were investigated for insecticidal potential. These microbes live in a diverse relationship with insects that may vary from beneficial to pathogenic.

RESULTS

Enterococcus casseliflavus, Enterococcus mundtii, Serratia marcescens, Klebsiella pneumoniae, Pseudomonas paralactis and Pantoea brenneri were isolated from adults of S. litura. Screening of these microbial isolates for insecticidal potential against S. litura showed higher larval mortality due to K. pneumoniae and P. paralactis. These bacteria also negatively affected the development of insect along with significant decline in relative growth and consumption rate as well as efficiency of conversion of ingested and digested food of insect. The bacteria significantly decreased the reproductive potential of insect. Perturbations in the composition of gut microbiome and damage to gut epithelium were also observed that might be associated with decreased survival of this insect.

CONCLUSIONS

Our study reveals the toxic effects of K. pneumoniae and P. paralactis on biology of S. litura. These bacteria may be used as potential candidates for developing ecofriendly strategies to manage this insect pest.

Dynamics of Zea mays transcriptome in response to a polyphagous herbivore, Spodoptera litura

Zea mays defense response is well-crafted according to the physical and chemical weapons utilized by their invaders during the coevolutionary period. Maize plants employ diversified defense strategies and alter the spatiotemporal distribution of several classes of defensive compounds to affect insect herbivore performance. However, only little knowledge is available about the defense orchestration of maize in response to Spodoptera litura, a voracious Noctuidae pest. In order to decipher the defense status of Zea mays (African tall variety) against S. litura, a comparative feeding bioassay was executed, which revealed reduced performance of the herbivore on maize. In order to understand the molecular mechanism behind maize tolerance against S. litura, a microarray-based genome-wide expression analysis was performed. The comparative analysis displayed 792 differentially expressed genes (DEGs), wherein 357 genes were upregulated and 435 genes were downregulated at fold change ≥ 2 and p value ≤ 0.05. The upregulated genes were identified and categorized as defense-related, oxidative stress-related, transcription regulatory genes, protein synthesis genes, phytohormone-related, and primary and secondary metabolism-related. In contrast, downregulated genes were mainly associated with plant growth and development, indicating a balance of growth and defense response and utilization of a highly evolved C-diversion response were noticed. Maize plants showed better tolerance against herbivory and maintained its fitness using a combinatorial strategy. This peculiar response of Zea mays against S. litura offers an excellent possibility of managing polyphagous pests by spicing up the plant's defensive response with tolerance mechanism.

Photoregime Affects Development, Reproduction, and Flight Performance of the Invasive Fall Armyworm (Lepidoptera: Noctuidae) in China

The migratory fall armyworm, Spodoptera frugiperda (Smith), has become a worldwide agricultural pest. In this study, the effects of photoregime on the development, reproduction, and flight performance of fall armyworm were assessed based on two-sex life tables, ovarian and testis anatomy, and flight mill tests. The results indicated that photoregime had a significant effect on developmental duration of fall armyworm individuals, pupal survival and emergence, and adult fecundity. Among seven photoregimes tested, the 16:8 (L:D) h photoregime was the most suitable for fall armyworm fitness with the shortest pre-oviposition period and mean generation period (T), highest mating frequency and mating rate of female moths, largest intrinsic rate of natural increase (rm) and finite rate of increase (λ), and highest net reproduction rate (R0). Population growth for seven different photoregimes in decreasing order was 16:8 (L:D) h > 8:16 (L:D) h > 12:12 (L:D) h > 10:14 (L:D) h > 14:10 (L:D) h > 0:24 (L:D) h > 24:0 (L:D) h. The ovarian development level, mating frequency, and testis size did not significantly differ between long (16:8 (L:D) h) and short (10:14 (L:D) h) illumination. Photoregime had a significant effect on mass loss during flight of adults, but not on flight velocity, flight duration, and flight distance. These findings can be used to refine laboratory rearing protocols, accurately predict seasonal changes in population dynamics and should help improve regional forecasts and management of the fall armyworm.

Lead stress affects the reproduction of Spodoptera litura but not by regulating the vitellogenin gene promoter

Lead (Pb) stress affects hormone-mediated responses (e.g., reproduction) in insects. In this study, the effects of Pb stress (12.5-50 mg Pb/kg in larval artificial diets) on the reproduction of the common cutworm Spodoptera litura (Lepidoptera: Noctuidae) were investigated after 7 generations. The results showed that Pb stress did not reduce the longevity of adult females, but 50 mg Pb/kg significantly reduced the longevity of adult males, regardless of the generation. After 50 mg Pb/kg stress for one or 7 generations, the peak time of egg-laying was delayed, and egg production and hatchability were decreased significantly. The vitellin content in eggs was significantly inhibited by Pb stress. The S. litura vitellogenin (Vg) gene promoter was cloned and analyzed. Multiple putative transcription factors were predicted for the 2321 bp Vg promoter region, including the TATA box, GATA, basic helix-loop-helix (bHLH) transcription factor, Broad-Complex (BR-C) binding sites, etc. The fragment from -2222 to -211 bp of the Vg promoter was the activation domain for Vg, whereas the region from -211 to -55 bp repressed the activity of the Vg promoter. The construct promoter (-782/+76) in Trichoplusia ni (Hi5) cells significantly improved Vg expression, which was not affected by Pb stress (1 or 10 mg/ml). Therefore, Pb stress significantly inhibited the reproduction of S. litura but not by regulating the Vg promoter.

Interspecific and Seasonal Variation in Wingbeat Frequency Among Migratory Lepidoptera in Northern China

Many lepidopteran species rely upon active flight to migrate over long distances, thus pursuing ephemeral resources, colonizing new habitats, or escaping adverse meteorological conditions. Though their biology and ecology are often well studied, there is only scant information on their wingbeat frequency (WBF), a key aerodynamic determinant of insect flight. In this study, we assessed interspecific and seasonal variability in WBF for 85 different migratory species of Lepidoptera (11 families) under the laboratory conditions of 25 ± 1°C and 75 ± 5% RH. WBF of migrant individuals ranged between 6.7 and 84.5 Hz and substantial interspecific differences were recorded, with members of the Bombycidae exhibiting the highest mean WBFs (i.e., 55.1 ± 1.0 Hz) and Saturniidae the lowest (8.5 ± 0.2 Hz). At a species level, seasonal variation was observed in WBF for Mythimna separata (Walker) (Lepidoptera: Noctuidae), Scotogramma trifolii Rottemberg (Lepidoptera: Noctuidae), and Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae). Our findings add to the scientific knowledge on flight biology of migratory insects, facilitate (automatic) monitoring and population forecasting, and can have broader implications for insect pest management or biodiversity conservation.

Dispersal of the Common Cutworm, Spodoptera litura, Monitored by Searchlight Trap and Relationship with Occurrence of Soybean Leaf Damage

The common cutworm, Spodoptera litura Fabricius (Lepidoptera: Noctuidae) is a major pest of soybean. Pheromone traps are used to monitor male adults, but the catch peaks do not always predict leaf damage in soybean fields. Thus, there is no accurate means of forecasting soybean damage, and insecticide is applied on the basis of farmers’ observations of actual damage in fields. To understand the occurrence of soybean leaf damage, the dispersal of S. litura in a soybean field in southwestern Japan was preliminarily investigated using a searchlight trap in comparison to a pheromone trap at one location, from August to mid-October in 2016–2018. To determine the relationship between pest arrival and crop damage, trap catch numbers and the number of soybean leaves damaged by 1st-instar larvae were examined by separately comparing raw numbers and cumulative numbers. The raw catch numbers of the two trap types in August and September 2016 and 2018 preceded subsequent damage peaks by an average of 5.3 days. This temporal difference coincided with the estimated duration of the egg stage plus an assumed mating period. Furthermore, the cumulative catch numbers of the two traps in August and September were linearly associated with cumulative damaged leaves in the same period in each year and in the three-year period. The coefficient of determination (R²) of linear regression between the cumulative catch numbers of the searchlight trap and the cumulative damaged leaves for the three-year period was much higher than that between the cumulative catch of the pheromone trap and cumulative damage. This suggests that soybean leaf damage is closely linked to the number of S. litura arrivals at the survey site. Thus, the searchlight trap captured S. litura arrivals better than the pheromone trap. As the linear regression function of the cumulative catch of the searchlight trap for the three-year period was tentatively correlated with a prefectural economic injury level for soybean fields, it might be feasible to predict S. litura-induced soybean damage using searchlight traps. The cumulative female catch number of the searchlight trap was also linearly associated with damaged leaves, but the coefficient of determination was generally lower than that with the cumulative total catch. The female ratio of searchlight trap catches in September was <0.5 in contrast to S. litura migrating overseas (>0.5). The advantages and disadvantages of the two trapping methods, as well as necessary further studies are discussed. Our findings provide a foundation for S. litura monitoring with searchlight traps.

Seasonal Migration Patterns of Ostrinia furnacalis (Lepidoptera: Crambidae) Across the Bohai Strait in Northern China

The Asian corn borer (ACB), Ostrinia furnacalis (Guenée), is a notorious polyphagous insect pest in China and other regions of East Asia. The long-distance flight behavior of the ACB moths, however, is not well understood, especially in the field conditions. In this study, nightly monitoring data for multiple years (2003-2017) on the long-distance flight of adults crossing the Bohai Strait in northern China, showed that a large number of the adults frequently flew across the Bohai Strait from May to September with the peak migrations usually occurred, followed in order by September, June, July, and May, and the number of southward migrants was larger than that of northward migrants. From May to September in 2010, 2011, and 2017, a subsample of trapped ACB females was dissected (879 individuals in 2010, 197 individuals in 2011, and 247 individuals in 2017), and the results showed that the sex ratio of the trapped ACB moths was unbiased each month from May to September. While the proportion of mated females in northward populations (May to July = 92.85 ± 4.86%) was significantly higher than that in southward population (August and September = 74.53 ± 8.55%) . The seasonal pattern in the proportion of sexually mature females was similar to the above proportion of mated females. We conclude that the ACBs have a strong propensity and ability for long-distance migration, although local dispersal is generally considered to be the primary movement of the ACB. These findings may be helpful to improve the forecasting systems and the pest management schemes for the ACBs.

Modeling Migratory Flight in the Spruce Budworm: Circadian Rhythm

The crepuscular (evening) circadian rhythm of adult spruce budworm (Choristoneura fumiferana (Clem.)) flight activity under the influence of changing evening temperatures is described using a mathematical model. This description is intended for inclusion in a comprehensive model of spruce budworm flight activity leading to the simulation of mass migration events. The model for the temporal likelihood of moth emigration flight is calibrated using numerous observations of flight activity in the moth’s natural environment. Results indicate an accurate description of moth evening flight activity using a temporal function covering the period around sunset and modified by evening temperature conditions. The moth’s crepuscular flight activity is typically coincident with the evening transition of the atmospheric boundary layer from turbulent daytime to stable nocturnal conditions. The possible interactions between moth flight activity and the evening boundary layer transition, with favorable wind and temperature conditions leading to massive and potentially successful migration events, as well as the potential impact of climate change on this process, are discussed.

Pest categorisation of Spodoptera litura

The EFSA Panel on Plant Health (PLHP) performed a pest categorisation of Spodoptera litura (Lepidoptera: Noctuidae) for the EU. S. litura is widely distributed across South and East Asia and Oceania. It is established in tropical and subtropical regions where there are no, or few, frost days each year. It can extend its range into cooler temperate regions during summer months. S. litura is highly polyphagous feeding on hosts within at least 40 botanical families, including economically important crops within Brassicaceae, Cucurbitaceae, Fabaceae, Malvaceae, Poaceae and Solanaceae. Larvae are primarily leaf feeders and can cause complete defoliation. At high population densities almost all plant parts are eaten. S. litura is a serious pest in the Asia‐Pacific region where it causes losses to many economically important cultivated field crops and crops such as eggplants, sweet peppers and tomatoes in protected cultivation. As a species that appears limited by winter temperatures, only a small area of the EU provides climatic conditions where establishment outdoors may be possible although cultivated and wild hosts are distributed across the EU. S. litura has been intercepted in the EU many times on ornamentals and leafy vegetables. Outbreaks have occurred in EU glasshouses and have been eradicated. Phytosanitary measures are available to inhibit entry. S. litura satisfies the criteria that are within the remit of EFSA to assess for it to be regarded as a potential Union quarantine pest. S. litura does not meet the criteria of occurring in the EU, and plants for planting being the principal means of spread for it to be regarded as a potential Union regulated non‐quarantine pest.

Migratory Helicoverpa armigera (Lepidoptera: Noctuidae) Exhibits Marked Seasonal Variation in Morphology and Fitness

Many insects adopt seasonal, trans-latitudinal migration in response to altering climatic conditions, resource availability or reproductive requirements. Though the migration behavior of the cotton bollworm, Helicoverpa armigera (Hübner)(Lepidoptera: Noctuidae), has been well-studied, little is known about the extent of intra-specific variation between northward- and southward-migrating individuals. In this study, we captured H. armigera adults along the species' migration route during 2017-2018 to determine seasonal variability in their morphology, flight capability, and reproductive performance. Northward migrants have broader, longer bodies and are 1.33 times heavier than southward migrants, hinting at a comparatively higher allocation of resources in the abdomen. Accordingly, the former migrants engaged in longer flights, had greater reproductive capacity and a longer lifespan than southward ones. As northward migrants originate from favorable environmental conditions, their fitness is higher than that of the southward cohorts that develop on less favorable host plants and in perhaps more adverse climatic or ecological conditions. Northward H. armigera migrants thus possess an advantageous morphology that benefits habitat colonization and resource exploitation. Our work offers a novel perspective on the ecological and reproductive benefits of long-distance migration and can aid the development of population monitoring and forecasting methods for this globally important agricultural pest.

Pest risk assessment of Spodoptera frugiperda for the European Union

EFSA was asked for a partial risk assessment of Spodoptera frugiperda for the territory of the EU focussing on the main pathways for entry, factors affecting establishment, risk reduction options and pest management. As a polyphagous pest, five commodity pathways were examined in detail. Aggregating across these and other pathways, we estimate that tens of thousands to over a million individual larvae could enter the EU annually on host commodities. Instigating risk reduction options on sweetcorn, a principal host, reduces entry on that pathway 100‐fold. However, sweetcorn imports are a small proportion of all S. frugiperda host imports, several of which are already regulated and further regulation is estimated to reduce the median number entering over all pathways by approximately 10%. Low temperatures limit the area for establishment but small areas of Spain, Italy and Greece can provide climatic conditions suitable for establishment. If infested imported commodities are distributed across the EU in proportion to consumer population, a few hundreds to a few thousands of individuals would reach NUTS 2 regions within which suitable conditions for establishment exist. Although S. frugiperda is a known migrant, entry directly into the EU from extant populations in sub‐Saharan Africa is judged not feasible. However, if S. frugiperda were to establish in North Africa, in the range of thousands to over two million adults could seasonally migrate into the southern EU. Entry into suitable NUTS2 areas via migration will be greater than via commercial trade but is contingent on the establishment of S. frugiperda in North Africa. The likelihood of entry of the pest via natural dispersal could only be mitigated via control of the pest in Africa. If S. frugiperda were to arrive and become a pest of maize in the EU, Integrated Pest Management (IPM) or broad spectrum insecticides currently used against existing pests could be applied.

Identification of Migratory Insects from their Physical Features using a Decision-Tree Support Vector Machine and its Application to Radar Entomology

Migration is a key process in the population dynamics of numerous insect species, including many that are pests or vectors of disease. Identification of insect migrants is critically important to studies of insect migration. Radar is an effective means of monitoring nocturnal insect migrants. However, species identification of migrating insects is often unachievable with current radar technology. Special-purpose entomological radar can measure radar cross-sections (RCSs) from which the insect mass, wingbeat frequency and body length-to-width ratio (a measure of morphological form) can be estimated. These features may be valuable for species identification. This paper explores the identification of insect migrants based on the mass, wingbeat frequency and length-to-width ratio, and body length is also introduced to assess the benefit of adding another variable. A total of 23 species of migratory insects captured by a searchlight trap are used to develop a classification model based on decision-tree support vector machine method. The results reveal that the identification accuracy exceeds 80% for all species if the mass, wingbeat frequency and length-to-width ratio are utilized, and the addition of body length is shown to further increase accuracy. It is also shown that improving the precision of the measurements leads to increased identification accuracy.

Trans-regional migration of the beet armyworm, Spodoptera exigua (Lepidoptera: Noctuidae), in North-East Asia

The beet armyworm, Spodoptera exigua (Hübner) (Lepidoptera: Noctuidae), is a serious polyphagous insect pest worldwide. This species is known as a long-distance migrant, and previous studies on its migration have been mostly carried out in regions where it can overwinter. However, what pattern of seasonal migration this species exhibits in regions where it cannot overwinter (i.e., the ‘summer breeding region’) remains unknown. Here, we present data from 14-years of monitoring on a small remote island located in the center of the Bohai Strait, in northern China, by means of searchlight trapping and ovarian dissection. We found that the population size of this overseas migration varied significantly among years, with very large migrations in 2005, 2007, 2009, and 2014 that resulted in annual total catches of more than ten thousand individuals. In addition, nightly catches exhibited a significant inter-month variability, with the vast majority of S. exigua moths being trapped in August and September, (81.1 ± 3.6%), making S. exigua one of the most frequently encountered species in that period. The mean time from the earliest trap capture to the latest capture within a given year was 113 ± 22 d (range 57 d [2003] to 138 d [2008]). The sex ratio (females: males) was significantly less than 1:1 in each month, but the proportion of females showed an upward trend from June to October. The majority of trapped females in summer were mated (94.4 ± 10.7% in June, 80.0 ± 6.4% in July) and sexually mature (88.9 ± 11.1% in June, 61.8 ± 12.3% in July), suggesting the onset of mating and/or sexual maturation does not terminate the migration behavior in this species. These findings provide a good starting point for study of the trans-regional migration of S. exigua across different climate zones.

Responses of the cutworm Spodoptera litura (Lepidoptera: Noctuidae) to two Bt corn hybrids expressing Cry1Ab

To examine the responses of the secondary lepidopteran pest Spodoptera litura to two Bacillus thuringiensis (Bt) corn hybrids [5422Bt1 (Event Bt11), 5422CBCL (MON810)] expressing Cry1Ab, larval bioassays with Cry1Ab toxin, corn leaves or kernels and bagging on corn plants were conducted. The results showed that larvae displayed a similar performance when fed kernels, but not leaves of 5422Bt1, 5422CBCL and their near-isogenic non-Bt corn (5422). Significantly higher Cry1Ab amounts were detected in larvae fed leaves than kernels of both Bt hybrids, with different molecular weights of protein band in plants (72 and 90 kDa for 5422Bt1 and 5422CBCL, respectively), gut contents (65 kDa), feces (50 kDa), which indicated that larvae had lower ingestion, higher degradation and excretion of Cry1Ab when fed kernels not leaves of both Bt hybrids. Significantly higher levels of cadherin-like receptors and alkaline phosphatase transcripts were detected in larvae fed leaves than kernels of two Bt hybrids. Catalase, superoxide dismutase and glutathione-S-transferase activities in larvae fed 5422Bt1 leaves were significantly higher than that of 5422 treatments. Therefore, S. litura had low susceptibility to 5422Bt1 and 5422CBCL when larvae fed kernels not leaves of Bt corn. Additionally, S. litura presented a much stronger tolerance to 5422CBCL than 5422Bt1.

Is Heliothis viriplaca (Lepidoptera: Noctuidae) a long-distance migrant?

Heliothis viriplaca (Hüfnagel) (Lepidoptera: Noctuidae) is an important polyphagous pest of beans, cotton, maize, and alfalfa worldwide. H. viriplaca is a long-distance migrant, and if so, what pattern of seasonal migration this species exhibits in northern China remains unknown. In this study, in order to determine the seasonal migration of H. viriplaca in northern China, the combination of searchlight trapping and ovarian dissection was carried out on an isolated small island in the center of the Bohai Strait during 2003-2014. The results confirmed that H. viriplaca undertakes long-distance migration on the prevailing winds of the East Asian monsoon airflows. This species exhibited a regular pattern of seasonal migration across the sea from May to October, but there was considerable yearly and monthly variation in the trapped numbers, with the majority being trapped in summer (67.99 ± 6.54%). The mean period when migration was detectable at the island was 116.5 ± 5.6 days from 2003 to 2014, with the shortest time span of 74 days in 2013 and the longest of 144 days in 2005. Trapped females in May and June showed a relatively higher mating rates and some degree of ovarian development when compared with July, August and September, suggesting the migration of this species is not completely bound by the 'oogenesis-flight syndrome'. These findings will be helpful to improve the forecasting system and managing strategies of H. viriplaca.