Spodoptera Frugiperda Research Articles

Courtship Behavior of Adult Spodoptera frugiperda (Lepidoptera: Noctuidae) Observed Using Track 3D Trajectory Tracking.

Spodoptera frugiperda, also known as the fall armyworm (FAW), is classified by the Food and Agriculture Organization of the United Nations (FAO) as a major agricultural pest. By gaining a more nuanced understanding of the fall armyworm's courtship behavior, simpler and more environmentally friendly methods of controlling this pest can be developed. This study used the Track 3D system to meticulously record and describe the activity characteristics and patterns of adult males and females during courtship. The results show that adult FAWs engaged in a variety of activities during courtship that were either discrete (flying, flapping, moving, and crawling), continuous (flapping + flying, flapping + crawling, and flying + crawling), or combined (flapping + touching + flapping; flying + touching + flying). Flying and flapping were the most common activities, with observed flight patterns consisting of parabolic, circular, and zigzag trajectories. The peak activity times for adult FAWs are mainly concentrated at 11:00 p.m., 3:00 a.m., and 5:00 a.m., providing fundamental data for the precise attraction and control of adult FAWs at later stages.

Effects of continuous and transgenerational rearing in peanut leaves on the performance and enzyme activity of Spodoptera frugiperda (Lepidoptera: Noctuidae).

The invasive fall armyworm (FAW), Spodoptera frugiperda, is a polyphagous pest that significantly threatens crops worldwide. FAW may undergo adaptation, enhancing its ability to infect specific plant hosts. However, there is limited knowledge on this topic. After 8 generations of constant rearing on peanut leaves, the performance and enzyme activities of FAW were investigated in this study. Compared to FAW fed on the peanut cultivars 'Fuhua 8' and 'Quanhonghua 1' for 2 generations, those grown on leaves for 5 to 8 generations had significantly shorter pre-adult development times and total preoviposition periods. Fecundity also increased significantly, resulting in an overall improvement in population fitness as measured by demographic parameters. However, the F2 generation of FAW fed on corn leaves outperformed the F8 generation of FAW fed on peanut leaves. In the F2 generation, the FAW peanut population exhibited 30-55% supernumerary larval molts, which decreased substantially in the F5 and F8 generations. Notably, supernumerary larval molts displayed pupation and emergence rates comparable to normal larvae, regardless of the peanut cultivar or rearing generation. The activities of lipase and acetylcholinesterase increased significantly from the F2 to F8 generations, showing substantial negative and positive correlations with larval development time and fecundity, respectively. In conclusion, FAW demonstrated inferior performance on peanut leaves compared to corn leaves, despite its performance was significantly improved after 5 to 8 generations of acclimation. These results suggest that corn will continue to be the primary target crop for FAW in China.

Maize plants can recover from fall armyworm damage under optimum crop production conditions in humid tropical agro-ecologies.

Farmers in Africa perceive the impact of fall armyworm (FAW) on maize to be significant, but field assessments have shown that yield losses are not significant enough to warrant pesticide interventions. This suggests that relationships between the crop stages, time, and duration of attack can affect the yield. Therefore, assessing the plant's recovery from damage using individual plants based on defoliation levels could guide whether and when pesticides should be applied. To study this, we selected 120 labeled maize plants corresponding to six levels of FAW defoliation, replicated 20 times, based on an initial damage rating. The rating scale ranged from 1 (no defoliation) to 5 (>75% defoliation) during four planting seasons. Plants with a rating scale of 1 were replicated and treated with a chemical insecticide to keep them undefoliated, and that served as a control. Damage severity was recorded weekly on all plants, starting from emergence until maturity, using the same damage rating scale. Results showed that damage severity varied significantly among different defoliation levels during all seasons. Higher levels of defoliation during dry seasons resulted in significant yield loss only for plants with damage levels 4 and 5, with damage severity ranging from 38.7% to 57.5%. These results indicate that FAW control is unnecessary in the rainy season. In contrast, pesticide interventions should be envisaged in seasons of erratic rainfall, with a significant defoliation threshold level of around 50%, occurring at 8 and 5wk after planting weeks after planting, respectively for the early and late dry season.

Effect of temperature and soil moisture on the infectivity of four species of entomopathogenic nematodes (Steinernema and Heterorhabditis spp.) to fall armyworm, Spodoptera frugiperda (Smith)

Spodoptera frugiperda (JE Smith) is one of the most important lepidopterous pests of maize throughout the word. The implementation of management strategies for this are need of the hour. In this case the use of Entomopathogenic nematodes (EPNs) is feasible because third-instar larvae feed in the leaf whorls of maize, and sixth instar larvae pupate in the soil; these two environments are congenial for the EPNs. But temperature and soil moisture play major roles in EPNs infectivity. Therefore, in the current study, we examined temperature and soil moisture effect on the infectivity of four indigenous EPN species from India, Heterorhabditis indica NBAIIH23, H. bacteriophora NBAIRH75, Steinernema carpocapsae NBAIRS59, and S. abbasi NBAIISa01 against larvae and pupae of S. frugiperda. Present study results showed that both temperature and soil moisture affected the infectivity of H. indica, S. carpocapsae, H. bacteriophora, and S. abbasi. As the exposure time increased, all these four nematodes infectivity to larvae was increased. Six days after inoculation, H. indica caused significantly higher larval mortality (96 %) at 25 °C and 100 % mortality at 28 °C. Whereas, S. carpocapsae caused 100 % mortality at 28 °C, and 76 % mortality at 25 °C. At 32 °C, H. indica and S. carpocapsae caused 90 % and 92 % larval mortality, respectively. As the temperature decreased to 20 °C, the infectivity of both the nematodes decreased. However, H. bacteriophora and S. abbasi caused 68 % and 50 % mortality in larvae at 20 °C, respectively. Compared to other nematodes, H. indica significantly caused higher mortality in pupae at 13 % soil moisture at 28 °C. We conclude that, Heterorhabditis indica and S. carpocapsae can be utilized against S. frugiperda larvae at (25–32 °C), and pupae at (28 °C). These nematodes can also be used against pupae of S. frugiperda at 9–13 % soil moisture content. We also suggest that these EPNs species can be incorporated in the Integrated Pest Management (IPM) for S. frugiperda.

Genetic Variation in the Invaded Population of the Fall Armyworm, Spodoptera frugiperda (J. E. Smith) (Lepidoptera: Noctuidae), in India

The fall armyworm, Spodoptera frugiperda, an invasive, polyphagous pest, causes significant damage to corn. The majority of insects rely on a broad range of digestive enzymes and an intricate detoxifying mechanism to consume chemically diverse host plants. The genetic variation in S. frugiperda was analyzed using cytochrome oxidase subunit I (COI) and triose phosphate isomerase (Tpi). In addition, a new attempt was made to determine the variation with respect to two detoxifying genes, viz., carboxylesterase and glutathione S-transferase. The highest genetic variation (3.03%) was found between the S. frugiperda populations of Tirupati and Delhi with respect to the Tpi gene and between the populations of Punjab and Hosur regarding COI (3.30%). The results for various genes revealed that populations of the fall armyworm were homogeneous, showing low genetic distance using COI, ranging from 0.40 to 3.30%, and, using Tpi, ranging from 0.43 to 3.03%. The variation in carboxylesterase and glutathione S-transferase ranged from 0.04 to 0.15% and from 0.01 to 0.02, respectively. Amino acid sequences were also produced using DNA sequences from several fall armyworm populations. Populations in Tirupati, Solapur, and Hyderabad shared 98.7% of their sequence with that in Delhi. Fall armyworm amino acid sequences showed 79.7 to 82.0% identity with S. exigua and 69.6 to 73.0% identity with S. litura. Our study provides vital information for understanding the genetic variation in the fall armyworm following its invasion of India.

Nano-pesticide delivery system based on UiO-66 with pH sensitivity for precise control of Spodoptera frugiperda.

Metal-organic frameworks have the advantages of easy synthesis, high loading capacity and good biocompatibility, making them essential materials for constructing pesticide nano-delivery systems. In this study, a pH-responsive nano-controlled-release formulation Chl@UiO-66 was prepared using UiO-66 as the nano-scale carrier for adsorbing chlorantraniliprole (Chl). The appearance, pesticide loading, release behaviour, insecticidal activity, long-term control efficacy and safety of Chl@UiO-66 for non-target organisms were extensively evaluated. The results showed that the prepared Chl@UiO-66 was a regular octahedron with a uniform particle size of 230 nm and pesticide loading of 15.62%. The release of pesticides under alkaline conditions was superior to that under acidic and neutral conditions, which showed pH-responsive performance. Chl@UiO-66 had an excellent ability to protect pesticides from ultraviolet degradation. Compared with chlorantraniliprole suspension concentrate, Chl@UiO-66 had a better control effect against Spodoptera frugiperda and long-term control efficacy. The prepared nano-controlled-release formulation had low toxicity to zebrafish, earthworms and human BEAS-2B cells. Chl@UiO-66 is a new pesticide formulation with high efficacy and low toxicity that provides a smart controlled-release solution. © 2024 Society of Chemical Industry.

The use of visual and olfactory cues by adult Spodoptera frugiperda (Lepidoptera: Noctuidae) while foraging.

The fall armyworm Spodoptera frugiperda (J.E. Smith; Lepidoptera: Noctuidae) is a notorious invasive insect pest. It is very important to understand the foraging behavior of this pest to develop more effective lures to monitor the immigration of this pest. In this study, the use of visual and olfactory cues in the foraging behavior of S. frugiperda was investigated through an attraction experiment in which color (produced from 8 different colored artificial flowers), odor (produced from honey water), and odorous color (produced from artificial flowers supplemented with honey water) were used. When we used 8 different colors to elicit adult responses, S. frugiperda showed a significant color preference despite limited activity (i.e., the total number of visits to the attractant), with black being the most preferred color, followed by orange preferred by both sexes and blue and green preferred only by females. When honey water was used as an attractant, S. frugiperda had relatively greater odor activity than color activity. When we sprayed the artificial flowers with honey, S. frugiperda showed even greater activity in terms of odor color than in terms of color or odor. Compared with male S. frugiperda, female adult S. frugiperda presented greater activity in response to all types of attractants. These findings suggest that S. frugiperda adults rely primarily on olfaction for foraging, with vision as a secondary sense, and that the combined use of olfactory and visual cues increases foraging efficiency. These results provide reference data for designing trapping strategies to monitor and control S. frugiperda.

Catechol acetylglucose: a newly identified benzoxazinoid-regulated defensive metabolite in maize.

An enormous diversity of specialized metabolites is produced in the plant kingdom, with each individual plant synthesizing thousands of these compounds. Previous research showed that benzoxazinoids, the most abundant class of specialized metabolites in maize, also function as signaling molecules by regulating the production callose as a defense response. We searched for additional benzoxazinoid-regulated specialized metabolites, characterized them, examined whether they too function in herbivore protection, and determined how Spodoptera frugiperda (fall armyworm), a prominent maize pest, copes with these metabolites. We identified catechol acetylglucose (CAG) as a benzoxazinoid-regulated metabolite that is produced from salicylic acid via catechol and catechol glucoside. Genome-wide association studies of CAG abundance identified a gene encoding a predicted acetyltransferase. Knockout of this gene resulted in maize plants that lack CAG and over-accumulate catechol glucoside. Upon tissue disruption, maize plants accumulate catechol, which inhibits S. frugiperda growth. Analysis of caterpillar frass showed that S. frugiperda detoxifies catechol by glycosylation, and the efficiency of catechol glycosylation was correlated with S. frugiperda growth on a catechol-containing diet. Thus, the success of S. frugiperda as an agricultural pest may depend partly on its ability to detoxify catechol, which is produced as a defensive metabolite by maize.

Energy Reserve Allocation in the Trade-Off between Migration and Reproduction in Fall Armyworm.

Striking a trade-off between migration and reproduction becomes imperative during long-range migration to ensure proper energy allocation. However, the mechanisms involved in this trade-off remain poorly understood. Here, we used a takeoff assay to distinguish migratory from non-migratory individuals in the fall armyworm, which is a major migratory insect worldwide. Migratory females displayed delayed ovarian development and flew further and faster than non-migratory females during tethered flight. Transcriptome analyses demonstrated an enrichment of fatty acid genes across successive levels of ovarian development and different migratory behaviors. Additionally, genes with roles in phototransduction and carbohydrate digestion along with absorption function were enriched in migratory females. Consistent with this, we identified increased abdominal lipids in migratory females that were mobilized to supply energy to the flight muscles in the thorax. Our study reveals that the fall armyworm faces a trade-off in allocating abdominal triglycerides between migration and reproduction during flight. The findings provide valuable insights for future research on this trade-off and highlight the key energy components involved in this strategic balance.

Host adaptability of Microplitis manilae (Hymenoptera: Braconidae) in Noctuidae.

Biological control is an effective and sustainable method of integrated pest management. Microplitis manilae (Hymenoptera: Braconidae) is a common internal parasitoid wasp of the order Lepidoptera. To determine a suitable host species for the reproduction of parasitoids, it is essential to assess host suitability and parasitic potential of the parasitized pests. Herein, we investigated host selection and exploitation of M. manilae. We evaluated the parasitic efficacy of M. manilae in 4 pest species in the Spodoptera and Mythimna genera of the Noctuidae family. The results indicated that the parasitism rate of M. manilae on 3 species in the Spodoptera genus is higher than on Mythimna separata in the Mythimna genus, with M. manilae exhibiting a higher parasitism rate and shorter development duration on Spodoptera litura compared to other species. The parasitism rate for 1st instars hosts was 86.67 ± 0.04%, while the development duration was 14.1 ± 0.03 days. However, when parasitizing the 3rd instar of Spodoptera frugiperda, parasitoids showed a higher sex ratio, of 0.71 ± 0.05. Additionally, M. manilae had parasitic effect on M. separata, providing a new choice for its parasitism. The results identify the optimal host, which could enhance and reproduction rate and survival rate of M. manilae, thus facilitating their large-scale propagation. Understanding the parasitic effects of M. manilae on pests can further its field application, also plays a major role in promoting the development of biological control technologies and sustainable agricultural production.

Comprehensive Transcriptomic Analysis Reveals Defense-Related Genes and Pathways of Rice Plants in Response to Fall Armyworm (Spodoptera frugiperda) Infestation.

Rice (Oryza sativa L.) serves as a substitute for bread and is a staple food for half of the world's population, but it is heavily affected by insect pests. The fall armyworm (Spodoptera frugiperda) is a highly destructive pest, threatening rice and other crops in tropical regions. Despite its significance, little is known about the molecular mechanisms underlying rice's response to fall armyworm infestation. In this study, we used transcriptome analysis to explore the global changes in gene expression in rice leaves during a 1 h and 12 h fall armyworm feeding. The results reveal 2695 and 6264 differentially expressed genes (DEGs) at 1 and 12 h post-infestation, respectively. Gene Ontology (GO) and KEGG enrichment analyses provide insights into biological processes and pathways affected by fall armyworm feeding. Key genes associated with hormone regulation, defense metabolic pathways, and antioxidant and detoxification processes were upregulated, suggesting the involvement of jasmonic acid (JA) signaling, salicylic acid biosynthesis pathways, auxin response, and heat shock proteins in defense during 1 h and 12 h after fall armyworm infestation. Similarly, key genes involved in transcriptional regulation and defense mechanisms reveal the activation of calmodulins, transcription factors (TFs), and genes related to secondary metabolite biosynthesis. Additionally, MYB, WRKY, and ethylene-responsive factors (ERFs) are identified as crucial TF families in rice's defense response. This study provides a comprehensive understanding of the molecular dynamics in rice responding to fall armyworm infestation, offering valuable insights for developing pest-resistant rice varieties and enhancing global food security. The identified genes and pathways provide an extensive array of genomic resources that can be used for further genetic investigation into rice herbivore resistance. This also suggests that rice plants may have evolved strategies against herbivorous insects. It also lays the groundwork for novel pest-resistance techniques for rice.

SVT 55: A High Yielding Rabi Sorghum Variety with Multiple Pest Tolerance

SVT 55 is a high yielding Rabi sorghum culture identified at Agricultural Research Station, Tandur, Professor Jayashankar Telangana State Agricultural University, Telangana and released by State Varietal Release Committee during 2023 in the name of Tandur Jonna 55 for the state of Telangana. It matures in 115-120 days and is adapted specifically to Rabi season. The culture recorded an average seed yield of 3245 kg/ha, with a mean grain yield advantage of 26 % over the popular check M 35-1and 12.3 % over the local check SVT 68 in the trials conducted during 2016-2022. The culture is moderately resistant to charcoal rot, recorded on par pest reaction score with respect to resistant checks for the insect pests of shoot fly, stem borer, aphids and fall army worm. It has high crude protein content (10.96 %) and good roti quality.

Automated lepidopteran pest developmental stages classification via transfer learning framework.

The maize crop is highly susceptible to damage caused by its primary pests, which poses considerable challenges in manually identifying and controlling them at various larval developmental stages. To mitigate this issue, we propose an automated classification system aimed at identifying the different larval developmental stages of 23 instars of 4 major lepidopteran pests: the Asian corn borer, Ostrinia furnacalis (Guenée; Lepidoptera: Crambidae), the fall armyworm, Spodoptera frugiperda (J.E. Smith; Lepidoptera: Noctuidae), the oriental armyworm, Mythimna separata (Walker; Lepidoptera: Noctuidae), and the tobacco cutworm, Spodoptera litura (Fabricius; Lepidoptera: Noctuidae). Employing 5 distinct Convolutional Neural Network architectures-Convnext, Densenet121, Efficientnetv2, Mobilenet, and Resnet-we aimed to automate the process of identifying these larval developmental stages. Each model underwent fine-tuning using 2 different optimizers: stochastic gradient descent with momentum and adaptive moment estimation (Adam). Among the array of models tested, Densenet121, coupled with the Adam optimizer, exhibited the highest classification accuracy, achieving an impressive 96.65%. The configuration performed well in identifying the larval development stages of all 4 pests, with precision, recall, and F1 score evaluation indicators reaching 98.71%, 98.66%, and 98.66%, respectively. Notably, the model was ultimately tested in a natural field environment, demonstrating that Adam_Densenet121 model achieved an accuracy of 90% in identifying the 23 instars of the 4 pests. The application of transfer learning methodology showcased its effectiveness in automating the identification of larval developmental stages, underscoring promising implications for precision-integrated pest management strategies in agriculture.

The Threat of the Fall Armyworm to Asian Rice Production Is Amplified by the Brown Planthopper.

The recent invasion of the fall armyworm (FAW) into Asia not only has had a major impact on maize yield but is feared to also pose a risk to rice production. We hypothesized that the brown planthopper (BPH) may aggravate this risk based on a recently discovered mutualism between the planthopper and the rice striped stem borer. Here we show that BPH may indeed facilitate a shift of FAW to rice. FAW females were found to strongly prefer to oviposit on BPH-infested rice plants, which emitted significantly elevated levels of five volatile compounds. A synthetic mixture of these compounds had a potent stimulatory effect on ovipositing females. Although FAW caterpillars exhibited relatively poor growth on both uninfested and BPH-infested rice, a considerable portion completed their development on young plants. Moreover, FAW were found to readily pupate and survive in exceedingly moist soils typical for rice cultivation, further highlighting FAW's potential to switch to rice. We conclude that BPH, by changing the bouquet of volatiles emitted by rice plants, may greatly facilitate this switch. These findings, together with a current increase of nonflooded upland rice in Asia, warrant careful monitoring and specific control measures against FAW to safeguard Asian rice production.

Multi-omics analysis reveal the fall armyworm Spodoptera frugiperda tolerate high temperature by mediating chitin-related genes

Climate change facilitates the rapid invasion of agricultural pests, threatening global food security. The fall armyworm Spodoptera frugiperda is a highly polyphagous migratory pest tolerant to high temperatures, allowing its proliferation in harsh thermal environments. We aimed to demonstrate mechanisms of its high-temperature tolerance, particularly transcriptional and metabolic regulation, which are poorly understood. To achieve the aim, we examined the impact and mechanism of heat events on S. frugiperda by using multiple approaches: ecological measurements, transcriptomics, metabolomics, RNAi, and CRISPR/Cas9 technology. We observed that several physiological indices (larval survival rate, larval period, pupation rate, pupal weight, eclosion rate, and average fecundity) decreased as the temperature increased, with the 32 °C treatment displaying a significant difference from the control group at 26 °C. Significantly upregulated expression of genes encoding endochitinase and chitin deacetylase was observed in the chitin-binding, extracellular region, and carbohydrate metabolic process GO terms of hemolymph, fat body, and brain, exhibiting a tissue-specific pattern. Significantly enriched pathways (e.g., cutin, suberin, and wax biosynthesis; oxidative phosphorylation and cofactor biosynthesis; diverse amino acid biosynthesis and degradation; carbon metabolism; and energy metabolism), all of which are essential for S. frugiperda larvae to tolerate temperature, were found in metabolites that were expressed differently. Successful RNA interference targeting of the three chitin-related genes reduced gene expression levels and larval survival rate. Knockout of the endochitinase gene by using the CRISPR/Cas9 system significantly reduced the relative gene expression and increased sensitivity to high-temperature exposure. On the basis of our findings, theoretical foundations for understanding the high-temperature tolerance of S. frugiperda populations and latent genetic control strategies were established.

The Fall Armyworm Spodoptera frugiperda Found on Rice Oryza sativa L. in China: Their Host Strain, Oviposition Preference and Survival Rate on Rice and Maize

The fall armyworm (FAW), Spodoptera frugiperda, is a serious pest that threatens a range of important crops worldwide. It originated in America and rapidly dispersed throughout Africa and Asia in 2018. There are two subtypes, corn-strain (C-strain) and rice-strain (R-strain), that have different host plant preferences, and the individuals damaging maize in China were identified as C-strain. In the present study, we found FAW individuals damaging rice plants in the field of Guangdong Province, China. FAW larvae and male adults were collected, and the majority of FAWs were characterized as CO I R-strain Tpi C-strain, which is similar to the FAWs damaging maize in China. The FAW adults preferred laying eggs on maize plants more than on rice plants. Compared to those that were fed maize leaves, the FAW larvae were unable to survive when fed 4-week-old rice plants, whereas they could complete their life cycle on 2-week-old rice plants, for which the total survival rate was 8%. The pre-adult- and pupal-stage durations were prolonged, and the fecundity of adult females decreased. Thus, the FAWs found in paddy fields showed better fitness on maize than on rice in the laboratory. Owing to their low survival rate on rice plants, they were unlikely to damage paddy fields in large areas, but populations of FAWs in paddy fields should be monitored.

Feeding and Growth Response of Fall Armyworm Spodoptera frugiperda (Lepidoptera: Noctuidae) towards Different Host Plants.

The fall armyworm, Spodoptera frugiperda, is a major migratory polyphagous insect pest of various crops. The essential nutrient and mineral profile of the host plants determines the feeding fitness of herbivorous insects. As a result, the growth and development of insects is affected. To determine the effect of the nutrient and mineral profile of different host plants (maize, castor bean, cotton, cabbage, okra, and sugarcane) on the growth and development of S. frugiperda, biological parameters like larval weight, pupal weight (male/female), and feeding and growth indices were calculated. The proximate compositions such as crude protein, crude fat, crude fibre, and ash and mineral contents of the tested host plants showed significant differences (p < 0.05). The feeding indices on these host plants also differed significantly (p < 0.05). The maximum relative growth rate (RGR), relative consumption rate (RCR), and consumption index (CI) were recorded in S. frugiperda larvae that fed on maize and castor bean leaves. The crude protein, dry matter, and ash contents in maize and castor bean were significantly higher and positively correlated with the RGR and RCR of S. frugiperda larvae. The larval, male and female pupal weights were the maximum in the larvae feeding on the castor bean host plant. These findings provide novel information based on nutritional ecology to develop sustainable integrated pest management strategies using selective crop rotation.

A spray-induced gene silencing strategy for Spodoptera frugiperda oviposition inhibition using nanomaterial-encapsulated dsEcR

Although RNAi-based pest management holds great potential as an alternative to traditional chemical control, its efficiency is restricted by dsRNA instability and limited cellular uptake. Using nanomaterials to facilitate dsRNA delivery has shown promise in solving these challenges. In this study, we firstly used RNAi to investigate the role of the juvenile hormone and ecdysteroid signaling pathways genes in reproduction of Spodoptera frugiperda, the fall armyworm. Females in knocked-down treatments of any of the Met, EcR, and USP genes had greatly reduced fertility with the most pronounced inhibitory effects on oviposition observed following EcR knockdown, and thus the dsEcR could be a candidate target for RNAi-based oviposition inhibitory agency. Then a combinatorial spray-induced and nanocarrier-delivered gene silencing (SI-NDGS) approach that targeted EcR was conducted. At 72 h post-spay, the transcript levels of EcR and the oviposition were successfully reduced and inhibited. These findings support the groundwork for further developing novel RNAi-based pest management strategies for S. frugiperda.

Insecticide binding mode analysis and biological effects of acetylcholinesterase target-site resistance mutations in Spodoptera frugiperda

It is urgent to solve insecticide resistance issues for fall armyworm (FAW), Spodoptera frugiperda. Some acetylcholinesterase-1 (Ace-1) mutations (A201S, G227A and F290V) have been identified as a cause of FAW resistance to organophosphates (OPs) and carbamates insecticides (CXs). However, the structural biological mechanisms on the relationship between the Ace-1 mutations and resistance to OPs and CXs still remain elusive. In this study, the A201S and F290V mutaions were found in eight fields populations of FAW except the G227A. Molecular docking revealed that the four Ace-1 proteins (Ace1-WT, Ace1-A201S, Ace1-G227A and Ace1-F290V) had the same binding modes and the same binding energies with acetylcholine (Ach), trichlorfon, chlorpyrifos, methomyl, carbaryl and chlorpyrifos oxide. The structural biological analysis revealed that the A201S mutations can enhance enzyme catalytic efficiency by introducing the hydroxyl group (-OH) from serine which performed the same function as the main-chain -NH and enhanced the interaction with the carboxy oxygen of acetylcholine (Ach), and the F290V mutation can effectively improve FAW resistance to insecticides by increasing the likelihood of Ach to enter the enzyme's active center for phenylalanine replaced by smaller valine under insecticide inhibition conditions. The bioassays and age-stage-specific life table analysis of FAW-SS and FAW-F290V populations revealed that F290V mutation effectively contributed to FAW resistance with a low fitness cost. This study provides a theoretical basis for future pest resistance management.

Adaptive evolution of invasive fall armyworms to maize with potential involvement of Cytochrome P450 genes

BackgroundAn invasion occurs when introduced species establish and maintain stable populations in areas outside of their native habitat. Adaptive evolution has been proposed to contribute to this process. The fall armyworm (Spodoptera frugiperda) is one of the major pest insects infesting maize in both invaded and native areas. The invasion of this species was reported from West Africa in 2016, followed by spreading across the Old World. We tested adaptive evolution to maize using 56 native samples from the USA and 59 invasive samples from Senegal, based on genomic and transcriptomic analyses.ResultsPrincipal component analysis revealed that the Senegalese population originated from corn strain. Three genetic loci were identified as targets of selective sweeps in the Senegalese population. These loci include four Cytochrome P450 genes (CYP321B1, CYP321B3, CYP321B4, and CYP337B5), as well as 12 genes of which the function is unclear. Transcriptomic analysis showed an overexpression of CYP321B1 and CYP321B3 genes in sfC samples compared to sfR samples. Additionally, these two genes were overexpressed when corn strain samples were exposed to maize. In larval feeding assays, the Senegalese population exhibited higher survival rates than a Floridan population across all four tested maize varieties.ConclusionsThese results suggest that the analyzed Senegalese population experienced adaptive evolution involving loci containing CYP genes, potentially associated with an increase in the survival rates on maize. We argue that the invasive success of the fall armyworm is contributed by stabilizing selection to maize.