Comparison of larval performance and oviposition preference of Spodoptera frugiperda among three host plants: Potential risks to potato and tobacco crops

Fall armyworm (FAW), Spodoptera frugiperda (J.E. Smith), is a major polyphagous pest with the potential to seriously damage various crops. A better understanding of FAW's performance on different hosts may help to predict which plants will be attacked when the preferred host is absent, and facilitate the development of effective pest management practices. We compared the larval performance of FAW fed on maize with that of FAW fed on potato and tobacco, which are important crops in China, using an age-stage two-sex life table and adult female oviposition preference experiments. In cage experiments with potato, tobacco, or maize as the host, FAW reared on maize exhibited the strongest performance with shorter developmental time in the larval stage, longer longevity, and a higher reproductive rate in adults. Females oviposited on maize in preference to potato or tobacco. Compared with larvae fed on maize, those fed on potato and tobacco exhibited significantly lower survival, with only 31.61% and 8.13% developing to the adult stage, respectively. Several life table parameters, including the mean generation time (T), net reproductive rate (R₀), finite rate of increase (λ), and intrinsic rate of natural increase (r) were negatively affected in FAW fed on potato and tobacco. Our results support the preference–performance hypothesis, that is, that herbivore females maximize fitness by choosing host plants associated with strong larval performance. Although larvae and adults performed poorly on potato and tobacco, their offspring will be capable of establishing populations on them, posing a potential threat to these crops in China.     

Effects of intergenerational host plant alterations on developmental parameters of Spodoptera frugiperda (Lepidoptera: Noctuidae)

The fall armyworm (FAW), Spodoptera frugiperda (Smith), is known as a destructive moth pest of agricultural crops such as corn, rice, and sorghum. Recently, its damage threatens crops in Asian temperate regions due to its high migration ability. Two genetic types of FAW, a corn strain mostly found on corn and a rice strain associated with rice, have been reported. The objective of this study was to evaluate whether migrated corn-collected population of FAW could maintain its population on various seasonal plants including non-preferred Poaceae plants, with special emphasis on Jeju, Korea. Development-related parameters were compared after switching host plants including corn (C), Sudan grass (S), proso millet (M), and rye (R) when rearing FAW. Most developmental parameters showed dynamic changes according to sequential alternation of host plants with the progress of generations. When all R₀ (net reproductive rate) values were scaled by the R₀ in C to C alteration, the scaled values of other alterations were less than “1.0”, indicating less fitness than C to C alteration (R₀ value: 0.57 for C to S, 0.49 for C to M in F3 generation; 0.82 for S to S, 0.65 for S to M, and 0.58 for S to C in F4 generation, 0.50 for M to M, 0.59 for M to R, and 0.83 for M to C in F5 generation). Although our results did not show that S. frugiperda adapted perfectively on new host plants, this pest was able to successfully reproduce up to five generations with non-preferred host plants. Results indicate that winter crops such as rye might be hosts for migrated corn-preferred populations of S. frugiperda during winter after breeding three to four cycles on other host plants before winter if weather condition is allowed for its survival.     

Potential of a combination of entomopathogenic fungal strains and a non-ionic surfactant to control the fall armyworm (Spodoptera frugiperda)

The fall armyworm, Spodoptera frugiperda, is an emerging invasive pest in Taiwan that feeds on a wide range of crops and causes serious damage. Herein, an entomopathogenic fungal library (EFLib) was constructed to identify potential microbes to control FAW. Twenty-eight indigenous entomopathogenic fungi (EPF) were isolated and investigated for their potential pathogenicity, with Metarhizium pinghaense (Mp-NCHU-124) and Beauveria bassiana (Bb-NCHU-157) exerting dose-dependent effects on the 4th instar FAW larvae. The non-ionic surfactant Silwet L-77 rapidly killed FAW larvae after spraying at a concentration of 300 mg/kg and the toxic effect of Silwet L-77 on FAW larvae was dose-dependent. When the EPF isolates (10⁶ conidia/mL) were applied to FAW larvae in combination with the non-ionic surfactant Silwet L-77 (30–90 mg/kg), the mortality rate dramatically increased and the LT₅₀ reduced, with increased fungal mycosis (Mp-NCHU-124: 38% to 72% and Bb-NCHU-157: 20 to 62%), indicating the high compatibility of EPF with the non-ionic surfactant. Thus, the Silwet L-77+EPF combined formulation has potential for practical field application for FAW pest control and sustainable agriculture in the future.     

Factoring distribution and prevalence of Fall armyworm in southwest China

Host plant growth changing with environmental conditions can impact the distribution of herbivores. The generalist herbivore fall armyworm (FAW), Spodoptera frugiperda (J. E. Smith) (Lepidoptera: Noctuidae), is an invasive pest rapidly spreading across the world and has recently invaded southern China. We studied effects of environmental factors on the distribution of the fall armyworm and its host (maize) plant growth in the tropical mountainous area of Huize County, province of Yunnan, southwest China. Moreover, the relationships among the FAW distribution, environmental factors (altitude, temperature and humidity) and plant growth (mean kernel weight, kernel number per ear and ear weight) were analysed. The results showed that FAW predominated at altitude 1,243.3 m, temperature 21.4°C and humidity 82.1%. The host plant grew best at 1,200–1,312 m, 21.0–21.7°C and 81.2%–82.0%. Environmental factors indirectly influenced the distribution of FAW via the host plant growth. Compared with environmental factors, the host plant growth had a simplistic positive linear relationship with the density of FAW. FAW is less impacted by abiotic factors rather it determined by host plant prevalence, and thus the locations where maize plants grow best are preferred by FAW and should be the focus of insecticide applications. Understanding the distribution of FAW under various environmental conditions provides a valuable reference for Chinese maize production and food security.     

Transmission of nuclear polyhedrosis virus in laboratory population of the armyworm, Mythimna (Pseudaletia) separata

Armyworm, Mythimna (Pseudaletia) separata, a serious pest of 12 agricultural crops, was artificially infected with its nuclear polyhedrosis virus to study the modes of virus transmission among the laboratory population. Virus transmitted by transovum and transovarial modes passed through polyhedra-fed moths to their progeny.     

A Theoretical Approach to Analyze the Parametric Influence on Spatial Patterns of <Emphasis Type="Italic">Spodoptera frugiperda</Emphasis> (J.E. Smith) (Lepidoptera: Noctuidae) Populations

Studies of the influence of biological parameters on the spatial distribution of lepidopteran insects can provide useful information for managing agricultural pests, since the larvae of many species cause serious impacts on crops. Computational models to simulate the spatial dynamics of insect populations are increasingly used, because of their efficiency in representing insect movement. In this study, we used a cellular automata model to explore different patterns of population distribution of Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae), when the values of two biological parameters that are able to influence the spatial pattern (larval viability and adult longevity) are varied. We mapped the spatial patterns observed as the parameters varied. Additionally, by using population data for S. frugiperda obtained in different hosts under laboratory conditions, we were able to describe the expected spatial patterns occurring in corn, cotton, millet, and soybean crops based on the parameters varied. The results are discussed from the perspective of insect ecology and pest management. We concluded that computational approaches can be important tools to study the relationship between the biological parameters and spatial distributions of lepidopteran insect pests.     

Benefits and challenges of maintaining national plant pest lists: an analysis of agricultural pests in Bhutan

Developing and maintaining national plant pest lists helps fulfil international obligations for trading countries, and also provides a foundation for national biosecurity systems. However, if done, lists and analyses are rarely made publically available. We compiled a national plant pest list for Bhutan, a relatively small but agriculturally diverse country for which plant protection is a recent discipline. We treated this pest list as a case study to test the benefits and challenges of maintaining such lists. Six hundred and forty‐five pest species were recorded across 64 different crops. Of those, only 17.0% were listed for Bhutan in the widely used CABI Crop Protection Compendium. Most species (86.4%) were first recorded during the initial discovery phase (1985–88) of a long‐running European Community funded aid programme. Regular taxonomic changes means keeping pest lists up to date requires both effort and expertise (27.0% of the 407 species identified by 1988 have since undergone name changes). Confidence in taxonomic identifications reduced drastically as access to international expertise decreased, from about 69.1% of species being identified with high confidence prior to 1988 to 8.1% afterwards. Many recent records lacked reference material, and voucher specimens for older material are mostly located internationally, making any revision challenging. Of the best represented taxa, greatest taxonomic uncertainty was for nematodes and viruses. Similar patterns were evident for the 112 damaging pest species, defined as those that at least occasionally and locally cause significant losses or require management actions within Bhutan. Of the damaging pests identified to species, all but one was also recorded in India, Bhutan's most important trading partner, and only 16 were restricted to Asia. New damaging pests continue to be recorded, but only five species may represent new incursions since 1988. National pest lists are critical, but to be of greatest value they need to capture taxonomic uncertainty, and focus on pests of greatest significance. For most countries, the development, maintenance and use of a national plant pest list will require ongoing regional and global cooperation to overcome taxonomic impediments, and to maximise the benefits of such lists in terms of facilitating trade and guiding domestic biosecurity activities.     

Cry1F Resistance in Fall Armyworm Spodoptera frugiperda: Single Gene versus Pyramided Bt Maize

Evolution of insect resistance to transgenic crops containing Bacillus thuringiensis (Bt) genes is a serious threat to the sustainability of this technology. However, field resistance related to the reduced efficacy of Bt maize has not been documented in any lepidopteran pest in the mainland U.S. after 18 years of intensive Bt maize planting. Here we report compelling evidence of field resistance in the fall armyworm, Spodoptera frugiperda (J.E. Smith), to Cry1F maize (TC 3507) in the southeastern region of the U.S. An F₂ screen showed a surprisingly high (0.293) Cry1F resistance allele frequency in a population collected in 2011 from non-Bt maize in south Florida. Field populations from non-Bt maize in 2012–2013 exhibited 18.8-fold to >85.4-fold resistance to purified Cry1F protein and those collected from unexpectedly damaged Bt maize plants at several locations in Florida and North Carolina had >85.4-fold resistance. In addition, reduced efficacy and control failure of Cry1F maize against natural populations of S. frugiperda were documented in field trials using Cry1F-based and pyramided Bt maize products in south Florida. The Cry1F-resistant S. frugiperda also showed a low level of cross-resistance to Cry1A.105 and related maize products, but not to Cry2Ab2 or Vip3A. The occurrence of Cry1F resistance in the U.S. mainland populations of S. frugiperda likely represents migration of insects from Puerto Rico, indicating the great challenges faced in achieving effective resistance management for long-distance migratory pests like S. frugiperda.     

First report of the fall armyworm,Spodoptera frugiperda (Lepidoptera: Noctuidae), natural enemies from Africa

The fall armyworm (FAW), Spodoptera frugiperda, is a major pest of maize in North and South America. It was first reported from Africa in 2016 and currently established as a major invasive pest of maize. A survey was conducted to explore for natural enemies of the fall armyworm in Ethiopia, Kenya and Tanzania in 2017. Smallholder maize farms were randomly selected and surveyed in the three countries. Five different species of parasitoids were recovered from fall armyworm eggs and larvae, including four within the Hymenoptera and one Dipteran. These species are new associations with FAW and were never reported before from Africa, North and South America. In Ethiopia, Cotesia icipe was the dominant larval parasitoid with parasitism ranging from 33.8% to 45.3%, while in Kenya, the tachinid fly, Palexorista zonata, was the primary parasitoid with 12.5% parasitism. Charops ater and Coccygidium luteum were the most common parasitoids in Kenya and Tanzania with parasitism ranging from 6 to 12%, and 4 to 8.3%, respectively. Although fall armyworm has rapidly spread throughout these three countries, we were encouraged to see a reasonable level of biological control in place. This study is of paramount importance in designing a biological control program for fall armyworm, either through conservation of native natural enemies or augmentative release.     

Larval dispersal of the invasive fall armyworm,Spodoptera frugiperda,the exotic stemborer Chilo partellus,and indigenous maize stemborers in Africa

Larval dispersal either through ballooning or crawling results in a redistribution of the insect population and infestations within and between plants. In addition, invasive species, such as the fall armyworm (FAW), Spodoptera frugiperda (JE Smith) (Lepidoptera: Noctuidae), and the exotic stemborer Chilo partellus (Swinhoe) (Lepidoptera: Crambidae), may displace indigenous stemborers on maize in Africa. To test whether larval dispersal activity may play a role in the displacement of indigenous stemborers, larval dispersal was compared between FAW, C. partellus, and the indigenous species Busseola fusca (Fuller) and Sesamia calamistis (Hampson) (both Lepidoptera: Noctuidae). Twenty potted maize plants were infested with one batch of eggs either from stemborers (B. fusca, S. calamistis, or C. partellus) or from FAW and monitored in the greenhouse for ballooning activities. After egg hatching, both ballooning and non-ballooning larvae were identified according to species and counted. FAW neonate larvae had greater potential for ballooning off than stemborers, irrespective of species. For each species, more females dispersed than males, and their survival rate was higher than that of non-ballooning larvae. In addition, plant-to-plant larval movements were studied using 6.25-m² plots of caged maize in a completely randomized design with five replicates. FAW was found to have wider dispersal and plant damage potential than any of the stemborer species. In conclusion, in contrast to C. partellus, the invasive characteristic of FAW can be explained, in part, by its higher larval dispersal activity compared to stemborers. This difference in larval dispersal might also be considered in sampling plans for monitoring pest density in the field.     

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。     

Bt maize can provide non-chemical pest control and enhance food safety in China

China is the world's second-largest maize producer and consumer. In recent years, the invasive fall armyworm Spodoptera frugiperda (J.E. Smith) has adversely affected maize productivity and compromised food security. To mitigate pest-inflicted food shortages, China's Government issued biosafety certificates for two genetically modified (GM) Bt maize hybrids, Bt-Cry1Ab DBN9936 and Bt-Cry1Ab/Cry2Aj Ruifeng 125, in 2019. Here, we quantitatively assess the impact of both Bt maize hybrids on pest feeding damage, crop yield and food safety throughout China's maize belt. Without a need to resort to synthetic insecticides, Bt maize could mitigate lepidopteran pest pressure by 61.9–97.3%, avoid yield loss by 16.4–21.3% (range −11.9–99.2%) and lower mycotoxin contamination by 85.5–95.5% as compared to the prevailing non-Bt hybrids. Yield loss avoidance varied considerably between experimental sites and years, as mediated by on-site infestation pressure and pest identity. For either seed mixtures or block refuge arrangements, pest pressure was kept below established thresholds at 90% Bt maize coverage in Yunnan (where S. frugiperda was the dominant species) and 70% Bt maize coverage in other sites dominated by Helicoverpa armigera (Hübner) and Ostrinia furnacalis (Guenée). Drawing on experiences from other crop/pest systems, Bt maize in se can provide area-wide pest management and thus, contribute to a progressive phase-down of chemical pesticide use. Hence, when consciously paired with agroecological and biodiversity-based measures, GM insecticidal crops can ensure food and nutrition security, contribute to the sustainable intensification of China's agriculture and reduce food systems' environmental footprint.     

Microbiome of the larvae of Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae) from maize plants

Fall armyworm (FAW), Spodoptera frugiperda, is an invasive insect pest with a diverse host range threatening food security in the African continent by causing severe economic damage to staple maize crop. FAW like all other insects are associated with various microbiota that influence their several characteristics and activities. The microbiota of insects plays important roles in their growth, development and environmental adaptation to their host plants or animals and not much is known about microbiota of FAW in Nigeria. In this study, the microbial community of FAW larvae from maize plants in Nigeria was investigated using Illumina PE250 NovaSeq of 16S rRNA V3-V4 gene region. A total of 1,160,133 sequence reads that ranged from 83,794 to 145,475 were obtained. They span through 2 kingdoms: bacteria (99.59%) and archaea (0.37%), 37 phyla, 59 classes, 78 orders, 145 families and 285 genera. The dominant taxonomic group of bacteria across the larval samples were Proteobacteria (58.32%), Firmicutes (35.87%) and Bacteroidetes (4.02%). There were no significant differences in bacteria species diversity and richness among the individual fall armyworm larva and samples from different geographical regions. The relative abundance of Bacteria phyla and classes also showed no significant differences among the larval samples. Significant differences were documented in bacteria orders Acidobacteriales and Aeromonadales, family Acidobacteriaceae_ (Subgroup_1) and genera Novosphingobium and Pedobacter. The results indicate that the gut of FAW larvae harbours a diverse set of bacteria and archaea biota. Understanding their ecological and functional relevance would provide novel insight on potential approaches for their exploitation in the integrated management of FAW in the tropics.     

Cross-Resistance between Cry1 Proteins in Fall Armyworm (Spodoptera frugiperda) May Affect the Durability of Current Pyramided Bt Maize Hybrids in Brazil

Genetically modified plants expressing insecticidal proteins from Bacillus thuringiensis (Bt) offer valuable options for managing insect pests with considerable environmental and economic benefits. Despite the benefits provided by Bt crops, the continuous expression of these insecticidal proteins imposes strong selection for resistance in target pest populations. Bt maize (Zea mays) hybrids have been successful in controlling fall armyworm (Spodoptera frugiperda), the main maize pest in Brazil since 2008; however, field-evolved resistance to the protein Cry1F has recently been reported. Therefore it is important to assess the possibility of cross-resistance between Cry1F and other Cry proteins expressed in Bt maize hybrids. In this study, an F₂ screen followed by subsequent selection on MON 89034 maize was used to select an S. frugiperda strain (RR) able to survive on the Bt maize event MON 89034, which expresses the Cry1A.105 and Cry2Ab2 proteins. Field-collected insects from maize expressing the Cry1F protein (event TC1507) represented most of the positive (resistance allele-containing) (iso)families found. The RR strain showed high levels of resistance to Cry1F, which apparently also conferred high levels of cross resistance to Cry1A.105 and Cry1Ab, but had only low-level (10-fold) resistance to Cry2Ab2. Life history studies to investigate fitness costs associated with the resistance in RR strain revealed only small reductions in reproductive rate when compared to susceptible and heterozygous strains, but the RR strain produced 32.2% and 28.4% fewer females from each female relative to the SS and RS (pooled) strains, respectively. Consistent with the lack of significant resistance to Cry2Ab2, MON 89034 maize in combination with appropriate management practices continues to provide effective control of S. frugiperda in Brazil. Nevertheless, the occurrence of Cry1F resistance in S. frugiperda across Brazil, and the cross-resistance to Cry1Ab and Cry1A.105, indicates that current Cry1-based maize hybrids face a challenge in managing S. frugiperda in Brazil and highlights the importance of effective insect resistance management for these technologies.     

Eliminating host-mediated effects demonstrates Bt maize producing Cry1F has no adverse effects on the parasitoid Cotesia marginiventris

The fall armyworm, Spodoptera frugiperda (J. E. Smith) (Lepidoptera: Noctuidae), is an important pest of maize in the United States and many tropical areas in the western hemisphere. In 2001, Herculex I^® (Cry1F) maize was commercially planted in the United States to control Lepidoptera, including S. frugiperda. In 2006, a population of S. frugiperda was discovered in Puerto Rico that had evolved resistance to Cry1F maize in the field, making it the first well-documented case of an insect with field resistance to a plant producing protein from Bacillus thuringiensis (Bt). Using this resistant population, we conducted tri-trophic studies with a natural enemy of S. frugiperda. By using resistant S. frugiperda, we were able to overcome possible prey-mediated effects and avoid concerns about potential differences in laboratory- or field-derived Bt resistance. We used the Cry1F-resistant S. frugiperda to evaluate effects of Cry1F on Cotesia marginiventris (Cresson) (Hymenoptera: Braconidae), a larval endoparasitoid of S. frugiperda, over five generations. Our results clearly demonstrate that Cry1F maize does not affect development, parasitism, survivorship, sex ratio, longevity or fecundity of C. marginiventris when they parasitize Cry1F maize-fed S. frugiperda. Furthermore, the level of Cry1F protein in the leaves was strongly diluted when transferred from Bt maize to S. frugiperda and was not detected in larvae, cocoons or adults of C. marginiventris. Our results refute previous reports of C. marginiventris being harmed by Bt proteins and suggest that such results were caused by prey-mediated effects due to using Bt-susceptible lepidopteran hosts.     

Using field-evolved resistance to Cry1F maize in a lepidopteran pest to demonstrate no adverse effects of Cry1F on one of its major predators

Spodoptera frugiperda (JE Smith) represents the first documented case of field-evolved resistance to a genetically engineered crop expressing an insecticidal protein from Bacillus thuringiensis (Bt). In this case it was Cry1F-expressing maize (Mycogen 2A517). The ladybird beetle, Coleomegilla maculata, is a common and abundant predator that suppresses pest populations in maize and many other cropping systems. Its larvae and adults are polyphagous, feeding on aphids, thrips, lepidopteran eggs and larvae, as well as plant tissues. Thus, C. maculata may be exposed to Bt proteins expressed in genetically engineered crops by several pathways. Using Cry1F-resistant S. frugiperda larvae as prey, we evaluated the potential impact of Cry1F-expressing maize on several fitness parameters of C. maculata over two generations. Using Cry1F resistant prey removed any potential prey-mediated effects. Duration of larval and pupal stages, adult weight and female fecundity of C. maculata were not different when they were fed resistant S. frugiperda larvae reared on either Bt or control maize leaves during both generations. ELISA and insect-sensitive bioassays showed C. maculata were exposed to bioactive Cry1F protein. The insecticidal protein had no effect on C. maculata larvae, even though larvae contained 20?C32?ng of Cry1F/g by fresh weight. Over all, our results demonstrated that the Cry1F protein did not affect important fitness parameters of one of S. frugiperda??s major predators and that Cry1F protein did not accumulate but was strongly diluted when transferred during trophic interactions.     

Investigating the Molecular Mechanisms of Organophosphate and Pyrethroid Resistance in the Fall Armyworm Spodoptera frugiperda

The fall armyworm Spodoptera frugiperda is an economically important pest of small grain crops that occurs in all maize growing regions of the Americas. The intensive use of chemical pesticides for its control has led to the selection of resistant populations, however, to date, the molecular mechanisms underlying resistance have not been characterised. In this study the mechanisms involved in the resistance of two S. frugiperda strains collected in Brazil to chlorpyrifos (OP strain) or lambda-cyhalothrin (PYR strain) were investigated using molecular and genomic approaches. To examine the possible role of target-site insensitivity the genes encoding the organophosphate (acetylcholinesterase, AChE) and pyrethroid (voltage-gated sodium channel, VGSC) target-site proteins were PCR amplified. Sequencing of the S. frugiperda ace-1 gene identified several nucleotide changes in the OP strain when compared to a susceptible reference strain (SUS). These result in three amino acid substitutions, A201S, G227A and F290V, that have all been shown previously to confer organophosphate resistance in several other insect species. Sequencing of the gene encoding the VGSC in the PYR strain, identified mutations that result in three amino acid substitutions, T929I, L932F and L1014F, all of which have been shown previously to confer knockdown/super knockdown-type resistance in several arthropod species. To investigate the possible role of metabolic detoxification in the resistant phenotype of the OP and PYR stains all EST sequences available for S. frugiperda were used to design a gene-expression microarray. This was then used to compare gene expression in the resistant strains with the susceptible reference strain. Members of several gene families, previously implicated in metabolic resistance in other insects were found to be overexpressed in the resistant strains including glutathione S-transferases, cytochrome P450s and carboxylesterases. Taken together these results provide evidence that both target-site and metabolic mechanisms underlie the resistance of S. frugiperda to pyrethroids and organophosphates.