Fall Armyworm Larvae Research Articles

Dispersal Behavior Characters of Spodoptera frugiperda Larvae

The fall armyworm (FAW), Spodoptera frugiperda (J. E. Smith) (Lepidoptera: Noctuidae), is a major pest of corn worldwide. FAW larval dispersal is an important life strategy that influences FAW population distribution in corn fields and subsequent plant damage. We studied FAW larval dispersal in the laboratory with sticky plates placed around the test plant and a unidirectional airflow source. Crawling and ballooning were the main dispersal means of FAW larvae both within and between corn plants. All larval instars (1st–6th) could disperse by crawling, with crawling being the only dispersal mechanism for 4th–6th instars. By crawling, FAW larvae could reach all aboveground parts of a corn plant as well as adjacent corn plants where leaves overlapped. Ballooning was used primarily by 1st-3rd instar larvae, and the proportion of these larvae that used ballooning decreased with age. Ballooning was largely governed by the larva’s interaction with airflow. Airflow influenced the direction and distance of larval ballooning. With an airflow speed of about 0.05 m/s, 1st instars could travel up to 196 cm from the test plant, indicating that long-distance FAW larval dispersal depends on ballooning. These results increase our understanding of FAW larval dispersal and provide scientific information for the development of FAW monitoring and control strategies.

The invasive Spodoptera frugiperda (J.E. Smith) has displaced Ostrinia furnacalis (Guenée) as the dominant maize pest in the border area of southwestern China.

The invasive fall armyworm (FAW) Spodoptera frugiperda (Lepidoptera: Noctuidae) has widely colonized the tropics and subtropics of Asia. However, the impact on the succession of the Asiatic corn borer (ACB) Ostrinia furnacalis (Lepidoptera: Pyralidae), a perennial dominant stemborer of maize in these areas, remains elusive. Here we analyzed the predation relationship, mimicked population competition, and surveyed the pest populations in the border area of Yunnan (southwestern China). Laboratory assays revealed that the 2nd to 6th instar larvae of FAW preyed on ACB, and only the 4th and 5th instar larvae of ACB preyed on FAW (1st instar larvae only, 50% predation rate). The 6th instar FAW preyed on the 1st to 5th instar ACB with a theoretical maximum of 14.5-58.8 ACB individuals (per maize leaf) and 4.8-25.6 individuals (per tassel). When maize plants were infested with eggs of either FAW or ACB in field cage trials, maize damage was 77.6% and 50.6%, respectively, compared with 77.9% and 2.8% upon co-infestation. In field surveys conducted in 2019-2021, FAW density was significantly greater than that of ACB, which took a great impact on maize growth. Our findings indicate that FAW can outcompete ACB at both the individual and population levels, which may result in FAW becoming the dominant pest. These results provide a scientific basis for further analysis of the mechanism by which FAW invades new agricultural areas and offers early-warning strategies for pest management. © 2023 Society of Chemical Industry.

The Fall Armyworm, Spodoptera frugiperda (Lepidoptera: Noctuidae), Influences Nilaparvata lugens Population Growth Directly, by Preying on Its Eggs, and Indirectly, by Inducing Defenses in Rice.

The fall armyworm (FAW), Spodoptera frugiperda, has become one of the most important pests on corn in China since it invaded in 2019. Although FAW has not been reported to cause widespread damage to rice plants in China, it has been sporadically found feeding in the field. If FAW infests rice in China, the fitness of other insect pests on rice may be influenced. However, how FAW and other insect pests on rice interact remains unknown. In this study, we found that the infestation of FAW larvae on rice plants prolonged the developmental duration of the brown planthopper (BPH, Nilaparvata lugens (Stål)) eggs and plants damaged by gravid BPH females did not induce defenses that influenced the growth of FAW larvae. Moreover, co-infestation by FAW larvae on rice plants did not influence the attractiveness of volatiles emitted from BPH-infested plants to Anagrus nilaparvatae, an egg parasitoid of rice planthoppers. FAW larvae were able to prey on BPH eggs laid on rice plants and grew faster compared to those larvae that lacked available eggs. Studies revealed that the delay in the development of BPH eggs on FAW-infested plants was probably related to the increase in levels of jasmonoyl-isoleucine, abscisic acid and the defensive compounds in the rice leaf sheaths on which BPH eggs were laid. These findings indicate that, if FAW invades rice plants in China, the population density of BPH may be decreased by intraguild predation and induced plant defenses, whereas the population density of FAW may be increased.

Within-field crop diversity and landscape complexity decrease the abundance of fall armyworm larvae in maize cropping systems

The composition and spatial arrangement of multiple crop and non-crop habitats at a field and landscape levels have the potential to modify the abundance and structure of arthropod communities. In particular, semi-natural habitats can provide important life support functions to a range of natural enemies of agricultural pests. How such traits might affect generalist predators has poorly been considered in complex landscapes dominated by intercropping and trees within a mosaic of small-scale agricultural plots in Africa. The objective of the present study was to test the hypothesis that crop diversity and landscape complexity in maize cropping systems decrease the abundance of crop pests through natural regulation by generalist predators. For this purpose, we monitored the fall armyworm abundance and predation of sentinel larvae by predatory ants across a set of maize fields with contrasted within-field crop diversity and abundance of semi-natural vegetation including trees and shrubs in their surrounding landscape. A negative effect of crop diversity and landscape complexity on FAW abundance, and a species-specific effect on ant abundance, were observed. However, no significant effect of ant abundance or predation on FAW abundance was observed, suggesting that habitat complexity by itself or other natural enemy communities such as parasitoids could play a complementary role to explain FAW abundance in maize crops.

Preference and performance of the fall armyworm, Spodoptera frugiperda, on six cereal crop species

AbstractThe fall armyworm (FAW), Spodoptera frugiperda (JE Smith) (Lepidoptera: Noctuidae), is a major migratory invasive pest that poses a severe threat to agricultural production and food security in China. In this study, we estimated the effects of six cereal crops on the development, survival, and fecundity of FAW using the age‐stage, two‐sex life table: maize (Zea mays L.), wheat (Triticum aestivum L.), sorghum [Sorghum bicolor (L.) Moench], oats (Avena sativa L.), millet (species, authority) (all Poaceae), and quinoa (Chenopodium quinoa Willd.) (Amaranthaceae). In a six‐choice test using detached leaf material, FAW larvae preferentially occurred on maize, followed by sorghum, within 6–24 h, and occurred the least on millet and quinoa. After 24 h, they had consumed the most leaf material from sorghum and maize, and the least from quinoa. In no‐choice tests using detached leaf material, they performed best on maize in terms of development (e.g., short development time), survival (e.g., high larval survival and pupation rate), and fecundity (e.g., high number of oviposition days and number of eggs laid per female), resulting in the highest predicted population growth (e.g., high intrinsic rate of increase and net reproductive rate). Although maize was found to be the most appropriate host plant, FAW was able to complete its life cycle on all six tested cereals. Our findings can help in predicting population dynamics and deepening our understanding of the potential damage incurred by FAW infestation, especially in regions under maize cultivation.

Efficacy of Selected Insecticides in Combination with Economic Thresholds in Managing Fall Armyworm (Lepidoptera: Noctuidae) Larvae in Maize Grown in Mexico

Abstract In Mexico, conventional insecticides are the main tools used to manage the fall armyworm, Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae), in maize, Zea mays L. This scenario results in the need to continually assess the biological efficacy of insecticides used to combat this pest. In this study, we evaluated the efficacy of insecticides with different modes of action in diverse locations under different levels of S. frugiperda larval infestation. The insecticides evaluated decreased larval density per plant to levels below the recommended economic threshold (ET) of 2.0 larvae per 10 plants (0.2/plant), resulting in decreased levels of damage to the plant whorl. When applied at infestation levels below the ET, larval numbers remained below the ET for at least 7–14 d after application. In contrast, when applied with infestation levels above the recommended ET, the performance of some insecticides in terms of effectively reducing larval density decreased. We, however, found that Coragen® (chlorantraniliprole; FMC Agroquímica de México), Clavis® (thiodicarb + triflumuron; Bayer de México), and Pleo® 50 EC (pyridalyl; Valent de México) can be used under these conditions to provide adequate protection up to 21 d after application. The information obtained in our experiments confirms the need to adjust the current ET depending on the type of compound to be used, since the insecticides used performed more efficiently and for a long time at densities lower than 2.0 larvae per 10 plants.

Evaluating the effectiveness of isolated fungi against Fall armyworm (Spodoptera frugiperda)

Spodoptera frugiperda, also known as the fall armyworm (FAW), is a polyphagous, destructive, and internationally dispersed insect pest that poses a serious danger to the production of cereals in Africa. Entomopathogens are a safe and environmentally beneficial way to control insect infestations when the all types of insecticides being used to control FAW are linked to a range of serious human health problems from respiratory to cancer. The objective of this study was to identify fungi from local soil that were effective against S. frugiperda larvae. Aluminum foil was used to gather soil samples from various maize growing regions in Ethiopia. Fungi isolated from soil samples and suspended conidia preparation was done in the mycology lab of Addis Ababa University in Ethiopia. At Melkasa Agricultural Research Center a bioassay test was conducted on S. frugiperda larvae. Three replications and a fully randomized design was used to set up the six treatments for the experiment. Twenty FAW larvae (3rd instar) were put into sterile Petri dishes with a diameter of 9 cm and a filter paper lining. A new, unopened syringe was used to inject 3 ml of the suspended solution into each treatment. As a negative control, distilled and sterilized water was used. FAW larval mortality was measured and examined independently for each treatment using GLM, followed by a Tukey's HSD post-hoc test. The cumulative mortality rate (P = 0.0001) and second-day mortality rate (P = 0.001) showed a significant difference between regimens. These noteworthy variations were seen in third instar larvae. S. frugiperda larvae from isolation fungi F1 and F5 had the highest (96.67%) and lowest (80.0%) mean cumulative death rates. Under negative control, the mean cumulative mortality rate was 8.33%. The outcomes showed that S. frugiperda could potentially be controlled by fungal isolates found in maize fields. Conidial concentration, as well as field evaluation, characterisation, and species identification of isolate fungi, all require more study.

Effect of maize seed treatment on oviposition preference, larval performance and foliar damage of the fall armyworm

AbstractThe fall armyworm (FAW), Spodoptera frugiperda (J. E. Smith; Lepidoptera: Noctuidae), is an invasive pest that has recently become a major worldwide threat for maize production. Greatest crop yield reductions occur following damage by FAW larvae at early vegetative plant stages, between the first and second week after plant emergence. In this study, field and semi‐field experiments were carried out to assess the effect of cyantraniliprole‐based seed treatment on the protection of early stages of maize plants against FAW and the associated mechanisms. In the field, maize seed treatment using cyantraniliprole (Fortenza®) significantly reduced the percentage of infested seedlings (77%) and the percentage of seedlings with severe damage (86%) up to 3 weeks after emergence. In a choice situation, semi‐field experiments showed that gravid moths preferred to lay eggs on plants from untreated seeds (68%) rather than on plants from treated seeds. To the best of our knowledge, this is the first evidence that insecticide residues present in plant tissues deter oviposition of Noctuid moths. Seed treatment with cyantraniliprole also reduced plant infestation (65%) 10 days after artificial inoculation of neonate larvae at 3 weeks after plant emergence, reducing the severity of leaf damage (by 67%). Insecticide seed treatment is a relevant tool for the integrated pest management of the FAW in high‐value crops such as sweet corn, especially for reducing foliar applications of insecticides during the most susceptible stages of the crop, as far as the risk of impacts on non‐target organisms is low and no alternative biocontrol option is available.

Interspecific Competition between Invasive Spodoptera frugiperda and Indigenous Helicoverpa armigera in Maize Fields of China

Since the fall armyworm (FAW) Spodoptera frugiperda invaded China, it has coexisted in maize fields with the native cotton bollworm (CBW) Helicoverpa armigera, but the population dynamics and competitive mechanisms between the two pests are not well understood. We evaluated interspecific competition between FAW and CBW by analyzing their bidirectional predation in the laboratory, survival rates when their larvae co-infested the same maize plant, and the population dynamics of both in the same maize field. In the predation tests, FAW and CBW larvae preyed on each other. However, the theoretical maximum predation of sixth-instar FAW larvae preying on first–second-instar CBW larvae was 71.4 and 32.3 individuals, respectively, while that of CBW was 38.5 and 28.6 individuals. The field co-infestation trials showed that the older larvae had a higher survival rate when the two pests co-infested the same maize plants, but young larval survival was higher for FAW than CBW. In the maize field from 2019 to 2021 in southern Yunnan, FAW populations were significantly higher than those of CBW. Our findings suggested that FAW larvae had a predation advantage over CBW, which might be an important reason for its dominance in Chinese maize fields. This result provides a scientific basis for developing a monitoring technology and for the integrated management of pests in invaded habitats of FAW.

Virulence of entomopathogenic fungi against fall armyworm, Spodoptera frugiperda (Lepidoptera: Noctuidae) under laboratory conditions.

Maize is an essential crop of China. The recent invasion of Spodoptera frugiperda, also known as fall armyworm (FAW), poses a danger to the country's ability to maintain a sustainable level of productivity from this core crop. Entomopathogenic fungi (EPF) Metarhizium anisopliae MA, Penicillium citrinum CTD-28 and CTD-2, Cladosporium sp. BM-8, Aspergillus sp. SE-25 and SE-5, Metarhizium sp. CA-7, and Syncephalastrum racemosum SR-23 were tested to determine their effectiveness in causing mortality in second instars, eggs, and neonate larvae. Metarhizium anisopliae MA, P. citrinum CTD-28, and Cladosporium sp. BM-8 caused the highest levels of egg mortality, with 86.0, 75.3, and 70.0%, respectively, followed by Penicillium sp. CTD-2 (60.0%). Additionally, M. anisopliae MA caused the highest neonatal mortality of 57.1%, followed by P. citrinum CTD-28 (40.7%). In addition, M. anisopliae MA, P. citrinum CTD-28, and Penicillium sp. CTD-2 decreased the feeding efficacy of second instar larvae of FAW by 77.8, 75.0, and 68.1%, respectively, followed by Cladosporium sp. BM-8 (59.7%). It is possible that EPF will play an important role as microbial agents against FAW after further research is conducted on the effectiveness of these EPF in the field.

Parámetros Biológicos de Spodoptera frugiperda1 Alimentado con Tres Hospederos

Spodoptera frugiperda (J.E. Smith) is the most important pest of maize and constitutes an ideal host for mass rearing of some natural enemies. Three substrates were tested: Zea mays, Cucurbita pepo, and Racinus communis to produce a more efficient and cheaper diet for mass production of S. frugiperda to be used as host. The life cycle of S. frugiperda did not differ in the duration of adult emergence between Z. mays (32.3 ± 0.4) and R. communis (32.8 ± 1.4), while C. pepo had the longest duration (37.0 ± 0.5). The difference in its biological cycle was observed when feeding larvae with R. communis leaves, which presented the best biological attributes such as higher percentage of egg hatching (95%), higher percentage of pupae (93%), higher percentage of adult emergence (78%), and higher number of eggs in the next generation (1,569 ± 32). Life tables showed low mortality rate (qx) and high life expectancy when fall armyworm larvae were fed R. communis. The logrank test indicated a difference between the different life tables between C. pepo and Z. mayz; C. pepo and R. communis; and R. communis and Z. mayz, with R. communis a better substrate for rearing S. frugiperda.

Direct and Indirect Infection Effects of Four Potent Fungal Isolates on the Survival and Performance of Fall Armyworm Larval Parasitoid Cotesia icipe

Fall armyworm (FAW), Spodoptera frugiperda, has recently invaded Africa where it is seriously threatening food security. Current management methods rely heavily on synthetic insecticides which are harmful to humans, the environment, and non-target beneficial insects. Cotesia icipe was recently identified as a major FAW-associated indigenous parasitoid causing a high parasitism rate on the pest in Kenya. Previous studies have demonstrated the efficacy of Metarhizium anisopliae ICIPE 7, ICIPE 41, ICIPE 78, and Beauveria bassiana ICIPE 621 against FAW. However, limited information is available on the interactions between these potent isolates and C. icipe. This study therefore assessed direct and indirect infection effects of these fungal isolates on C. icipe, induced 2nd instar FAW mortality, and parasitism rates of the infected C. icipe. Results showed that when C. icipe were directly exposed to dry conidia of the fungal isolates, ICIPE 7 and ICIPE 41 caused the highest (100%) C. icipe adult mortality seven days post-exposure. Both isolates also induced the highest FAW larval mortality of 55% and 53%, respectively. ICIPE 78 recorded the highest parasitism rates after direct infection. In the indirect exposure (fungal-infected FAW larvae exposed to the parasitoid), 1 × 109 conidia mL−1 recorded high C. icipe adult and FAW 2nd instar mortalities for all fungal isolates. This study provides an important baseline for effective fungal-based biopesticides development that could also be used in augmentative biological control. However, further studies are warranted to assess the performance of C. icipe in combination with these potent biopesticides in the field.

Repellent, antifeedant and toxic effects of plants-extracts against Spodoptera frugiperda larvae (fall armyworm)

The fall armyworm (FAW), Spodoptera frugiperda, is a polyphagous pest because of the damage it causes to crops. The utilization of plant extracts with bioactive compounds for controlling S. frugiperda has been emerging to be a new venture. Therefore, this study aimed at analyse the impact of Adathoda vassica, Dathura metel, and Tagetes erecta extracts against FAW. Leaves were washed, air dried (27 ± 2○C) and powdered and their extracts were obtained with ethyl acetate as a solvent. Bio efficacy of extracts was studied through different concentrations (0.2, 0.4, 0.6 μg/μL) against third instar larvae of S. frugiperda to assess the contact toxicity, antifeedant activity and repellency effect. The presence of phytochemicals i.e; tannins, terpenoids, phenols, saponins, flavonoids and alkaloids were determined and characterized using FTIR analysis. The T. erecta was more effective against FAW larvae that caused significantly very high (P < 0.05) antifeedant activity, and contact toxicity with the lowest LD50 (at all concentrations). The degree of repellency was greatly influenced by the concentration of the extract. Low Index of Repellency (IR), high Percent Repellency (PR) and residual PR were observed in T.erecta and D.metel and the highest significant value (P < 0.05) was observed in T.erecta. Therefore, T.erecta can be categorized into the highest repellency class (Class V). The phytochemical and FTIR analysis confirmed the presence of bioactive compounds having the potential against S. frugiperda. Therefore, D.metel and T. erecta are showing the potentiality for pesticidal development.

Assessment of Resistance Mechanisms to Fall Armyworm, Spodoptera frugiperda in Tropical Maize Inbred Lines

The fall armyworm (FAW), Spodoptera frugiperda, a pest of maize native to the Americas first reported in West and Central Africa in 2016, severely threatens maize production and food security in Sub-Saharan Africa. Native genetic resistance is one of the best methods of control of insect pests as it is contained in the seed making it more amenable for use by farmers compared to other interventions and it is also compatible with other integrated pest management (IPM) options. An intensive screening against FAW was carried out by artificial infestation in greenhouse conditions in Kenya between 2017 and 2018 on about 3000 inbred lines available in the germplasm collection of the International Maize and Wheat Improvement Center (CIMMYT). Among these lines, only four showed to be resistant to FAW, but the mechanisms of resistance are not yet known. The objective of this study was to determine the resistance mechanisms specifically non-preference and antibiosis to S. frugiperda in these four selected resistant inbred lines. The studies were conducted under laboratory and net house conditions in Kenya from April 2020 to November 2021. Non-preference was assessed estimating the feeding preference by counting the number of FAW neonates found on each leaf portion, silk portion and grain using binary and multiple choice methods under laboratory conditions, while antibiosis was assessed through the relative growth rate (RGR) and developmental time of FAW larvae on leaves, silks and grains under both laboratory and net house conditions. Among the four resistant maize inbred lines tested, two, namely CML71 and CKSBL10008, exhibited the highest level of antibiosis resistance on leaves. Under laboratory conditions, the larval RGR reduced from 13 mg/d on the most susceptible line to 8 mg/d on CML71. CML71 also showed a good non-preference on leaves compared to other tested lines. Only 6% of neonates choose to feed on CML71 whereas more than 10% choose to feed on the other lines (and 15% on the most susceptible) in multiple choice tests. The non-preference for feeding and lower RGR of larvae on CML71 suggest a biochemical involvement resistance to FAW. Through this study, CML71 is revealed as a highly promising line for use in breeding for native genetic resistance to FAW in tropical maize.

Acute and Persistent Toxicity of Newer Insecticide Molecules Against Invasive Pest of Maize, Fall Armyworm Spodoptera frugiperda (J.E.Smith)

Laboratory and pot culture experiments were conducted to assess the acute and persistent toxicity of new molecular insecticides against the notorious invasive pest of maize, Spodoptera frugiperda during 2020- 2021 at Department of Agricultural Entomology, Tamil Nadu Agricultural University, Coimbatore. Results revealed that, the LC50 value of emamectin benzoate, chlorantraniliprole, spinetoram, flubendiamide and novaluron were 0.05, 4.08, 0.1, 85.89 and 0.91 ppm, respectively for second instar larvae and 0.03, 5.63, 0.02, 162.99 and 0.99 ppm for third instar larvae of fall armyworm. Among insecticides tested emamectin benzoate and spinetoram showed high toxicity to S. frugiperda than other insecticides by registering a minimum LC50 value. But in the persistent toxicity studies, the same insecticides showed less persistence on maize crop. Hence, insecticides like flubendiamide and chlorantraniliprole need to be recommended in the early stage of the crop period (within 20 days after sowing) and less persistent insecticides viz., emamectin benzoate and spinetoram should be recommended in the middle stage (25 to 40 days) of the maize crop for the management of S. frugiperda so that the residues may not accumulate in the harvested produce both in the stalk and grain.

The effect of chlorantraniliprole on the transcriptomic profile of Spodoptera frugiperda: a typical case analysis for the response of a newly invaded pest to an old insecticide.

Chlorantraniliprole is a diamide insecticide widely used in China over the last 15 years. The fall armyworm (FAW), Spodoptera frugiperda, newly invaded China in 2019. The response of FAW to chlorantraniliprole deserves more attention, in the context of many destructive lepidopteran species are resistant to diamide insecticides and the patent on core chemical of chlorantraniliprole in China expired in August 2022. This study investigated the response profile in larvae under chlorantraniliprole-induced (LC50) stress using methods of bioassay, RNA-Seq and qPCR. We observed growth inhibition and lethal effects in FAW larvae, but at a relatively high LC50 value compared to other several pests. Additionally, under chlorantraniliprole-induced stress, 3309 unigenes were found to be differentially expressed genes. The impacted genes included 137 encoding for detoxification enzymes, 29 encoding for cuticle proteins, and 20 key enzymes involved in the chitin metabolism, which all associated with metabolic resistance. Finally, we obtained the single nucleotide polymorphisms (SNPs) of two RyR genes, which are the target proteins for chlorantraniliprole. We also investigated the causes of the high LC50 value in our FAW, which possibly related to the stabilized 4743M on SNP frequency of RyR. These findings documented the genetic background of RyR of FAW and indicated that application of chlorantraniliprole has a high risk of controlling FAW in China. In brief, our results provide a better understanding of the mechanisms of chlorantraniliprole toxicity and detoxification in FAW, and will aid in monitoring the development of resistant strains for a newly pest to an old insecticide.

Management of Fall Army Worm of Maize, Spodoptera frugiperda, with Green Synthesis Silver Nanoparticles

The fall armyworm (FAW), Spodoptera frugiperda is a polyphagous and economically important insect pest originated from tropical and sub-tropical parts of America. Being a strong flier, climatic adaptation and large host range makes it a serious threat to food security. It is responsible for high economic losses in many cash crops, vegetables and cereals. The overreliance and overuse of pesticides for the management of FAW posed many problems including insecticide resistance, resurgence of insect pests, biotype development and environmental hazards. To combat these problems, the most important alternative is the use of green synthesis nanoparticles and biocontrol agents which have been proven as eco-friendly technology for pest control. The current study was, therefore, planned to evaluate the toxicity of different plant based synthetic nanoparticles and biocontrol agent (Trichogramma spp.) against fall armyworm. Silver nanoparticles of neem resulted in the highest (83%) and the lowest (40%) mortality of 2nd instar larvae of FAW. However, the highest mortality due to silver nanoparticles of tobacco, onion, mint, ginger and datura was observed as 86%, 63%, 76%, 63% and 73% while the lowest mortality was 30%, 33%, 30%, 23% and 16% respectively. In view of the current findings nanoparticles of datura and neem could be recommended as potential bio-based chemicals for the control of S. frugiperda.

Reliability of Pheromone Trap Catches and Maize Plant Damage as Criteria for Timing Fall Armyworm Control Interventions in Humid Forest Agroecology of Central Africa.

Control of fall armyworm (FAW) Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae) since its invasion of Africa still depends on pesticides. Early detection of adults is considered the key to the success of larvae control in the crop field. However, FAW control thresholds based on current monitoring techniques are not well established in Africa. We investigated the efficacy of moth capture frequencies and FAW incidence levels as decision tools for FAW management. Experiments were conducted over two maize cropping seasons during which FAW incidence, severity, and larvae count were recorded during destructive sampling after the application of a homologated insecticide. During the first season, the FAW incidence ranged from 37.5 ± 5.6% in the 25% incidence threshold treatment to 48.1 ± 8.1% in the control. During the second season, the incidence was significantly lower in the 25% incidence threshold treatment (55.8 ± 5.7%) compared with the control (75.7 ± 3.0%). Over the two seasons, no significant difference in FAW damage severity was recorded between the treatments and control. The highest number of larvae per plant (4.0 ± 0.6) was observed in the 10% incidence threshold treatment. Insecticide application did not consistently contribute to reducing FAW incidence and observed plant damage did not translate into yield loss. FAW control needs further investigation to establish a threshold above which damage translates into yield loss, thus necessitating control intervention.

In Vitro Effectiveness of Beauveria bassiana as a Control Agent against Invasive Fall Armyworm (Spodoptera frugiperda) Larvae

Fall armyworm or Spodoptera frugiperda is one of the main pests of corn. It can caused up to 28.08% yield loss. Pest control efforts with broad-spectrum insecticides can cause negative impacts that disrupt ecosystems, non-target biotic factors and the surrounding environment. Beauveria bassiana is an alternative biological control agent that is target-specific. This study was conducted to determine toxic and antifeedant activities of B. bassiana application on third to fifth-instar S. frugiperda larvae. B. bassiana isolates were propagated using corn flakes media and resulted in colonies with conidia density of 1.1×108conidia.g-1. This study used a completely randomized design with 5 treatments and 5 replications. Treatments consisted of P1 namely B. bassiana propagation with a concentration of 60 g.L-1, P2 = 70 g.L-1, and P3 = 80 g.L-1. P0 was a negative control (untreated with B. bassiana) and P4 was a positive control (diazinon with concentrations of 2 ml.L-1). The variables observed were mortality and weight of the leftover feed. The results showed that the formulation of B. bassiana with concentrations of 80 g.L-1 was able to infect armyworms with a mortality percentage of 53.5% which was statistically similar as the effect of chemical insecticides. In addition, inhibition of feeding activity due to treatment could prevent leaf damage up to 68.21%.

ZmRop1 participates in maize defense response to the damage of Spodoptera frugiperda larvae through mediating ROS and soluble phenol production.

As plant-specific molecular switches, Rho-like GTPases (Rops) are vital for plant survival in response to biotic and abiotic stresses. However, their roles in plant defense response to phytophagous insect's damage are largely unknown. In this study, the expression levels of nine maize RAC family genes were analyzed after fall armyworm (FAW) larvae infestation. Among the analyzed genes, ZmRop1 was specifically and highly expressed, and its role in maize response to FAW larvae damage was studied. The results showed that upon FAW larvae infestation, salicylic acid and methyl jasmonate treatment ZmRop1 gene transcripts were all down-regulated. However, upon mechanical injury, the expression level of ZmRop1 was up-regulated. Overexpression of ZmRop1 gene in maize plants could improve maize plant resistance to FAW larvae damage. Conversely, silencing of ZmRop1 increased maize plant susceptibility to FAW larvae damage. The analysis of the potential anti-herbivore metabolites, showed that ZmRop1 promoted the enzyme activities of catalase, peroxidase and the expression levels of ZmCAT, ZmPOD, ZmRBOHA and ZmRBOHB, thereby enhancing the reactive oxygen species (ROS) production, including the content of O2- and H2O2. In addition, overexpression or silencing of ZmRop1 could have influence on the content of the total soluble phenol through mediating the activity of polyphenol oxidase. In summary, the results illuminated our understanding of how ZmRop1 participate in maize defense response to FAW larvae damage as a positive regulator through mediating ROS production and can be used as a reference for the green prevention and control of FAW larvae.