The Efficacy of Alternative, Environmentally Friendly Plant Protection Measures for Control of Fall Armyworm, Spodoptera Frugiperda, in Maize

Entomopathogenic nematodes as an effective and sustainable alternative to control the fall armyworm in Africa

The recent invasion of the fall armyworm (FAW), a voracious pest, into Africa and Asia has resulted in unprecedented increases in insecticide applications, especially in maize cultivation. The health and environmental hazards posed by these chemicals have prompted a call for alternative control practices. Entomopathogenic nematodes are highly lethal to the FAWs, but their application aboveground has been challenging. In this study, we report on season-long field trials with an innocuous biodegradable gel made from carboxymethyl cellulose containing local nematodes that we specifically developed to target the FAW. In several Rwandan maize fields with distinct climatic conditions and natural infestation rates, we compared armyworm presence and damage in control plots and plots that were treated with either our nematode gel formulation, a commercial liquid nematode formulation, or the commonly used contact insecticide cypermethrin. The treatments were applied to the whorl of each plant, which was repeated three to four times, at 2-week intervals, starting when the plants were still seedlings. Although all three treatments reduced leaf damage, only the gel formulation decreased caterpillar infestation by about 50% and yielded an additional ton of maize per hectare compared with untreated plots. Importantly, we believe that the use of nematodes can be cost-effective, since we used nematode doses across the whole season that were at least 3-fold lower than their normal application against belowground pests. The overall results imply that precisely formulated and easy-to-apply nematodes can be a highly effective, affordable, and sustainable alternative to insecticides for FAW control.

Transcriptomic and biochemical insights into fall armyworm (Spodoptera frugiperda) responses on silicon-treated maize

Background

The fall armyworm, Spodoptera frugiperda, is an agricultural pest of significant economic concern globally, known for its adaptability, pesticide resistance, and damage to key crops such as maize. Conventional chemical pesticides pose challenges, including the development of resistance and environmental pollution. The study aims to investigate an alternative solution: the application of soluble silicon (Si) sources to enhance plant resistance against the fall armyworm.

Methods

Silicon dioxide (SiO2) and potassium silicate (K2SiO3) were applied to maize plants via foliar spray. Transcriptomic and biochemical analyses were performed to study the gene expression changes in the fall armyworm feeding on Si-treated maize.

Results

Results indicated a significant impact on gene expression, with a large number of differentially expressed genes (DEGs) identified in both SiO2 and K2SiO3 treatments. Furthermore, Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis identified critical DEGs involved in specific pathways, including amino acid, carbohydrate, lipid, energy, xenobiotics metabolisms, signal transduction, and posttranslational modification, significantly altered at both Si sources. Biochemical analyses further revealed that Si treatments inhibited several enzyme activities (glutamate dehydrogenase, trehalase, glucose-6-phosphate dehydrogenase, chitinase, juvenile hormone esterase, and cyclooxygenase while simultaneously inducing others (total protein, lipopolysaccharide, fatty acid synthase, ATPase, and cytochrome P450), thus suggesting a toxic effect on the fall armyworm. In conclusion, Si applications on maize influence the gene expression and biochemical activities of the fall armyworm, potentially offering a sustainable pest management strategy.

Bionomic responses of Spodoptera frugiperda (J. E. Smith) to lethal and sublethal concentrations of selected insecticides

Since 2016, the invasive insect Spodoptera frugiperda (J. E. Smith) (Lepidoptera: Noctuidae) from the Americas has made maize production unattainable without pesticides in parts of Sub-Saharan Africa and Asia. To counteract this pest, farmers often resort to the use hazardous pesticides. This study aimed to investigate botanicals, microbials, and semi-synthetic insecticides in Ghana for pest control without harming local ecosystems. Under laboratory and on-station conditions, the present study evaluated the acute and sublethal responses of S. frugiperda to: (i) Pieris rapae Granulovirus (PrGV) + Bacillus thuringiensis sub sp. kurstaki (Btk) 5 WP, (ii) Btk + monosultap 55 WP, (iii) ethyl palmitate 5 SC, (iv) azadirachtin 0.3 SC, (v) acetamiprid (20 g/l) + λ-cyhalothrin (15 g/l) 35 EC, (vi) acetamiprid (30 g/l) + indoxacarb (16 g/l) 46 EC, and (vii) emamectin benzoate 1.9 EC. The results showed that at 96 hours post-exposure emamectin benzoate-based formulation has the highest acute larvicidal effect with lower LC50 values of 0.019 mL/L. However, the results suggested strong sublethal effects of PrGV + Btk, azadirachtin, and ethyl palmitate on the bionomics of S. frugiperda. Two seasons on-station experiments, showed that the semi-synthetic emamectin benzoate and the bioinsecticide PrGV + Btk are good candidates for managing S. frugiperda. The promising efficacy of emamectin benzoate and PrGV + Btk on the bionomics of S. frugiperda in the laboratory and on-station demonstrated that they are viable options for managing this pest.

Feature Refinement Method Based on the Two-Stage Detection Framework for Similar Pest Detection in the Field

Efficient pest identification and control is critical for ensuring food safety. Therefore, automatic detection of pests has high practical value for Integrated Pest Management (IPM). However, complex field environments and the similarity in appearance among pests can pose a significant challenge to the accurate identification of pests. In this paper, a feature refinement method designed for similar pest detection in the field based on the two-stage detection framework is proposed. Firstly, we designed a context feature enhancement module to enhance the feature expression ability of the network for different pests. Secondly, the adaptive feature fusion network was proposed to avoid the suboptimal problem of feature selection on a single scale. Finally, we designed a novel task separation network with different fusion features constructed for the classification task and the localization task. Our method was evaluated on the proposed dataset of similar pests named SimilarPest5 and achieved a mean average precision (mAP) of 72.7%, which was better than other advanced object detection methods.

The Effect of Wood Ash and Soil Applications on the Behavior and Survival of Spodoptera frugiperda (Lepidoptera: Noctuidae) Larvae on Maize

Cryptic feeding inside maize whorls makes it difficult to control fall armyworm (FAW). Smallholder farmers use alternative methods of control, of which the efficacy is uncertain. We determined the efficacy of wood ash and soil for the control of FAW and recorded its effect on larval preference and ballooning. Maize plants were artificially infested with larvae of different instars and treatments were either soil, wet ash, or dry ash, applied as single preventative or curative applications. Larvae exhibited non-preference for treated leaves in choice tests. The efficacy of treatments varied largely between experiments. Under laboratory conditions, ash treatments resulted in significant mortality of 1st and 5th instars. Dry and wet ash as curative applications for 1st instars resulted in 67 and 66% mortality, respectively, compared to mortality recorded in the control (22%). Under field conditions, survival of 3rd instars on treated plants was low (21-34%), compared to 70% on untreated plants. Due to the high variability in efficacy, the use of these alternative methods does not guarantee effective control. They do, however, have a place in IPM systems if applied as soon as infestations are observed and when larvae as still small. Recommendations on the use of ash and soil as spot treatments against FAW are provided.

One stone for two birds: Endophytic fungi promote maize seedlings growth and negatively impact the life history parameters of the fall armyworm, Spodoptera frugiperda

The fall armyworm (FAW) Spodoptera frugiperda, is a voracious pest of cereals native to the Americas and which invaded Africa in 2016. Chemical control is the main management option, which however remains ineffective and unsustainable. Fungal endophytes are increasingly used as alternative for the management of insect pests of economic importance. This study assessed the potential of eight endophytic fungal isolates to colonize maize plant and their ability to promote seedlings growth through seed and foliar inoculations, as well as their suppressive effects on FAW. Fungal colonization rates of different plant parts by the endophytes varied as per the inoculation methods. Beauveria bassiana ICIPE 279 colonized more than 60% of all the seedling parts while B. bassiana G1LU3 only colonized stem (25%) and leaf (5%) tissues through foliar inoculation. Trichoderma atroviride F2S21, T. asperellum M2RT4, T. harzianum F2R41, Trichoderma sp. F2L41, Hypocrea lixii F3ST1 and Fusarium proliferatum F2S51 successfully colonized all the plant parts and therefore were selected and further evaluated through seed inoculation for their endophytic persistence, effect on plant growth, and pathogenicity to Spodoptera frugiperda immature and adult stages. Weekly assessment showed varied effect of the endophytes on maize plant growth parameters compared to the control. During the first week, percentage colonization of the plant parts ranges between 90%-100%, 65%-100%, and 60%-100%, in the roots, stems, and leaves, respectively for all the five tested isolates. However, the colonization pattern/rates significantly decreased over time for H. lixii F3ST1 in the stems and leaves, and for T. harzianum F2R41 in the leaves and for T. asperellum M2RT4 in the roots. In addition, T. harzianum F2R41 outperformed all the other isolates in boosting the plant height, whereas H. lixii F3ST1 and T. asperellum M2RT4 outperformed all the other isolates in increasing the wet and dry shoots weight. Furthermore, the number of egg masses laid on endophytically-colonized maize plants varied among the treatments. Trichoderma asperellum M2RT4 and H. lixii F3ST1 endophytically-colonized maize plants significantly reduced the number of egg masses and the defoliation/feeding rates of the pest compared to the control. Additionally, T. harzianum F2R41 had the highest negative impact on the pupation and adult emergence of S. frugiperda with a female-biased sex ratio. Our findings indicate that T. asperellum M2RT4, T. harzianum F2R41, and H. lixii F3ST1 hold a potential to be developed as endophytic-fungal-based biopesticides for sustainable management of S. frugiperda and as plant growth promoters.

Chemical Control and Insecticide Resistance in Spodoptera frugiperda (Lepidoptera: Noctuidae)

Insecticides and genetically modified Bt crops are the main tools for control of the fall armyworm, Spodoptera frugiperda (J.E. Smith). Since its invasion of Africa, the Far East, and Australia where Bt crops are largely absent, insecticide use has increased and reduced susceptibility to several insecticides used for decades in its native distribution area have been reported. Poor efficacy at field-level is sometimes incorrectly ascribed to pest resistance, while numerous other factors influence efficacy at field-level. In this paper, we review the history of insecticide resistance in S. frugiperda and discuss the influence that life history traits, migration ecology, and chemical control practices may have on control efficacy and resistance evolution. The indirect role that poor national policies have on pesticide use practices, and indirectly on control efficacy and selection pressure is discussed. Evidence shows that local selection for resistance drives resistance evolution. Integrated pest management, rather than reliance on a single tactic, is the best way to suppress S. frugiperda numbers and the over-use of insecticides which selects for resistance.

Potential Management Options for the Invasive Moth Spodoptera frugiperda in Europe

We here review and discuss management options that growers in Europe could take in response to the expected invasion of the fall armyworm, Spodoptera frugiperda (Lepidoptera: Noctuidae). The focus is put on maize but the information provided is also relevant for other crops potentially affected. A sound forecasting system for fall armyworm both on a regional as well as at local scale should be established to alert growers as early as possible. Whilst a number of cultural control methods are adopted by maize growers in different regions globally to fight fall armyworm, many of them may either not be highly effective, too laborious, or otherwise unfeasible within the mechanized crop production systems used in Europe. Potential is seen in the stimulation of natural enemies through conservation biocontrol approaches, e.g., the planting of flower strips or intermediate cover crops, reducing tillage intensity, and avoiding broad-spectrum insecticides. To manage fall armyworm infestations, several effective biologically-based products are available globally, and some in Europe, e.g., based on specific baculoviruses, certain Bacillus thuringiensis strains, few entomopathogenic nematodes, and a number of botanicals. These should be given priority to avoid a major influx of insecticides into the maize agro-ecosystem once the fall armyworm arrives and in case growers are not prepared. Plant protection companies, particularly biocontrol companies should act proactively in starting registration of ingredients and products against fall armyworm in Europe. European maize growers should be made aware, in time, of key features of this new invasive pest and appropriate control options.

Exploring the Antioxidant and Bioinsecticidal Activity of Spontaneous Flora Vegetal Extracts for Plant Protection and Prevention of Soil Contamination

The purpose of this article was to evaluate the application of different plant extracts with bioinsecticidal action and antioxidant activity for plants and soil protection, by substitution of the application of synthetically formulated pesticides with eco-friendly compounds. In this framework, this research focused on the utilization of plant extracts from the spontaneous flora of Moldova (Romania) as bioinsecticides for the control of field pests of the species Leptinotarsa decemlineata and their antioxidant activity. Plant extracts of oregano (Origanum vulgare), yarrow (Achillea millefolium), wormwood (Artemisia absinthium), and cowslip (Primula veris) were assessed for their antioxidant activity by the microplate spectrophotometric-based method (for polyphenols and flavonoids content and for 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenger activity) and were characterized by FTIR spectroscopy spectra. To evaluate the bioinsecticidal properties of the plant extracts, the mortality (%) and neuroleptic manifestations appearing in the middle of the monitoring period for larvae and adults of the Leptinotarsa decemlineata species were identified. Mortality (%) was statistically analyzed using a one-way analysis of variance (ANOVA) and the resulting experimental results were compared with the LSD-Fisher’s test (p < 0.05). The highest mortality (%) was observed after 24 h of treatment with extracts of Origanum vulgare at 100% concentration, while the maximum effect was recorded after 48 h for Origanum vulgare at 60% and 100% concentrations.

Pesticide resistance in arthropods: Ecology matters too

Pesticide resistance development is an example of rapid contemporary evolution that poses immense challenges for agriculture. It typically evolves due to the strong directional selection that pesticide treatments exert on herbivorous arthropods. However, recent research suggests that some species are more prone to evolve pesticide resistance than others due to their evolutionary history and standing genetic variation. Generalist species might develop pesticide resistance especially rapidly due to pre‐adaptation to handle a wide array of plant allelochemicals. Moreover, research has shown that adaptation to novel host plants could lead to increased pesticide resistance. Exploring such cross‐resistance between host plant range evolution and pesticide resistance development from an ecological perspective is needed to understand its causes and consequences better. Much research has, however, been devoted to the molecular mechanisms underlying pesticide resistance while both the ecological contexts that could facilitate resistance evolution and the ecological consequences of cross‐resistance have been under‐studied. Here, we take an eco‐evolutionary approach and discuss circumstances that may facilitate cross‐resistance in arthropods and the consequences cross‐resistance may have for plant–arthropod interactions in both target and non‐target species and species interactions. Furthermore, we suggest future research avenues and practical implications of an increased ecological understanding of pesticide resistance evolution.

A cost-efficient and alternative technique of managing fall armyworm Spodoptera frugiperda (J.E. Smith) larvae in maize crop

An experiment was conducted to test the efficacy of grease and emamectin benzoate in a randomized complete block design with five replications to reduce fall armyworm, Spodoptera frugiperda (J.E. Smith) larvae load from a maize field in the winter seasons of 2020 and 2021 in Sarlahi, Nepal. Standard agronomic package of practices followed for crop proper growth and development, and plant spacing maintained at 20 × 60  cm² with a plot size of 390 m². The treatments were applied when the maize crop was at knee height and larvae damaged nearly 5-8% of the total plants. Emamectin benzoate sprayed at 0.4 g/liter of water and grease of about 0.15 g applied to the maize whorl or tip of a drooping leaf that touched the soil. A significant reduction in larval infestation was observed after 7-days of treatment applications. Fall armyworm larvae were found dead in the chemical-sprayed plots, but they were absent in the grease-applied fields. No crop damage was observed among the grease-treated plants, which might be due to restrictions in the movement of larvae on the maize crop. The armyworm larvae might get irritated, feel insecure, and move far away from the test plots searching for food materials. Thus, an eco-friendly material like grease can be used as an agroecological method for managing fall armyworm larvae among small-scale land-holding maize farmers.

Managing Fall Armyworm in Africa: Can Bt Maize Sustainably Improve Control?

The recent invasion of Africa by fall armyworm, Spodoptera frugiperda, a lepidopteran pest of maize and other crops, has heightened concerns about food security for millions of smallholder farmers. Maize genetically engineered to produce insecticidal proteins from the bacterium Bacillus thuringiensis (Bt) is a potentially useful tool for controlling fall armyworm and other lepidopteran pests of maize in Africa. In the Americas, however, fall armyworm rapidly evolved practical resistance to maize producing one Bt toxin (Cry1Ab or Cry1Fa). Also, aside from South Africa, Bt maize has not been approved for cultivation in Africa, where stakeholders in each nation will make decisions about its deployment. In the context of Africa, we address maize production and use; fall armyworm distribution, host range, and impact; fall armyworm control tactics other than Bt maize; and strategies to make Bt maize more sustainable and accessible to smallholders. We recommend mandated refuges of non-Bt maize or other non-Bt host plants of at least 50% of total maize hectares for single-toxin Bt maize and 20% for Bt maize producing two or more distinct toxins that are each highly effective against fall armyworm. The smallholder practices of planting more than one maize cultivar and intercropping maize with other fall armyworm host plants could facilitate compliance. We also propose creating and providing smallholder farmers access to Bt maize that produces four distinct Bt toxins encoded by linked genes in a single transgene cassette. Using this novel Bt maize as one component of integrated pest management could sustainably improve control of lepidopteran pests including fall armyworm.

Using Azadirachtin to Transform Spodoptera frugiperda from Pest to Natural Enemy

Spodoptera frugiperda and Rhopalosiphum maidis, as main pests, seriously harm the safety of maize. At present, chemical pesticides are mainly used to control these pests. However, due to residue and resistance problems, more green, environmentally benign, simple preventive control technology is needed. In this study, we reported the reason for the antifeedant activity of azadirachtin on S. frugiperda and proposed that S. frugiperda treated with azadirachtin would turn from pest into natural enemy. S. frugiperda showed an obvious antifeeding phenomenon to maize leaf treated with various azadirachtin concentrations (0.5~20 mg/L). It was found that maize leaf treated with 1 mg/L of azadirachtin has a stimulating effect on the antenna and sensillum basiconicum of S. frugiperda, and azadirachtin can affect the feeding behavior of S. frugiperda. Additionally, after treating maize leaves or maize leaves + R. maidis with 1 mg/L of azadirachtin, the predatory behavior of S. frugiperda changed from a preference for eating maize leaves to R. maidis. Moreover, the molting of R. maidis can promote the change of this predatory behavior. Our results, for the first time, propose that the combined control technology of azadirachtin insecticide and biological control could turn S. frugiperda from pest into natural enemy, which can effectively eliminate R. maidis and protect maize. This combined control technology provides a new way for pest management and has good ecological, environmental, and economic benefits.

Bio-Efficacy of Diatomaceous Earth, Household Soaps, and Neem Oil against Spodoptera frugiperda (Lepidoptera: Noctuidae) Larvae in Benin

Spodoptera frugiperda was first reported in Africa in 2016 and has since become a serious threat to maize/cereal production on the continent. Current control of the pest relies on synthetic chemical insecticides, which can negatively impact the environment and promote the development of resistance when used indiscriminately. Therefore, great attention is being paid to the development of safer alternatives. In this study, several biorational products and a semi-synthetic insecticide were evaluated. Two household soaps ("Palmida" and "Koto") and a detergent ("So Klin") were first tested for their efficacy against the larvae under laboratory conditions. Then, the efficacy of the most effective soap was evaluated in field conditions, along with PlantNeem (neem oil), Dezone (diatomaceous earth), and Emacot 19 EC (emamectin benzoate), in two districts, N'Dali and Adjohoun, located, respectively, in northern and southern Benin. The soaps and the detergent were highly toxic t second-instar larvae with 24 h lethal concentrations (LC50) of 0.46%, 0.44%, and 0.37% for So Klin, Koto, and Palmida, respectively. In field conditions, the biorational insecticides produced similar or better control than Emacot 19 EC. However, the highest maize grain yields of 7387 and 5308 kg/ha were recorded, respectively, with Dezone (N'Dali) and Emacot 19 EC (Adjohoun). A cost-benefit analysis showed that, compared to an untreated control, profits increased by up to 90% with the biorational insecticides and 166% with Emacot 19 EC. Therefore, the use of Palmida soap at 0.5% concentration, neem oil at 4.5 L/ha, and Dezone at 7.5 kg/ha could provide an effective, environmentally friendly, and sustainable management of S. frugiperda in maize.

Fall-armyworm invasion, control practices and resistance breeding in Sub-Saharan Africa

Fall armyworm [Spodoptera frugiperda (J.E. Smith); FAW] invasion has exacerbated maize (Zea mays L.) crop yield losses in sub-Saharan Africa (SSA), already threatened by other stresses, especially those that are climate-change induced. The FAW is difficult to control, manage, or eradicate, because it is polyphagous and trans-boundary, multiplies fast, has a short life cycle and migrates easily, and lacks the diapause growth phase. In this study, FAW and its impact in Africa was reviewed, as well as past and present control strategies for this pest. Pesticides, cultural practices, natural enemies, host-plant resistance, integrated pest management (IPM), and plant breeding approaches were examined as possible control strategies. It was concluded that an IPM control strategy, guided by cultural approaches already being used by farmers, and what can be adopted from the Americas, coupled with an insect-resistance management strategy, is the best option to manage this pest in Africa. These strategies will be strengthened by breeding for multi-trait host-plant resistance through stacking of genes for different modes of control of the pest.