Silicon enhanced wheat: Effects on development, oviposition preferences and mandibular wear in Oriental armyworm, Mythimna separata

OTUKA A., NIIYAMA T., JIANG X.

The first generation of the oriental armyworm, Mythimna separata (Walker), arrives every year in northern Japan in mainly late May to early June. Analyses of weather maps suggested that this moth's immigration source could be eastern China, but the accuracy of those analyses was very limited due to the lack of a current standard trajectory analysis. The management of migratory insect pests such as M. separata benefits from the identification of the pests' migration source(s) and pathway(s). The present study was a trajectory analysis for M. separata. Backward trajectories from trap sites in northern Japan were calculated with the HYSPLIT system developed by the U.S. National Oceanic and Atmospheric Administration, taking the moth's flight speed and the limitation of low ambient temperature at flight height into account. The ending times of the moth's short and long trajectories were set at dusk on the day before and 2 days before the possible arriving date, respectively. The results suggested two types of possible migration pathway: a multi-step pathway from Northeast China, the Korean Peninsula, and eastern Russia, which are destination areas of the first-generation's migration, and a direct pathway from seasonal main emigration areas in eastern China such as Jiangsu and Shandong provinces. These findings contribute to our understanding of M. separata's migration ecology and can be used for the development of methods to predict the migration of this insect.

Sousa A.C., Pinto C.P., dos Santos A.L., Fonseca S.S., Camargo M.S., Rossi G.D.

Sugarcane borer, Diatraea saccharalis, is one of the main insect pests of sugarcane fields, and it has been mainly managed by the use of chemical or biological controls. Considering the benefits of Silicon (Si) fertilization against pests, it was assessed the development of sugarcane borer larvae and sugarcane growth with and without Si. A greenhouse experiment was conducted using a factorial design (2 × 2) with 10 repetitions. Two commercial sugarcane varieties were evaluated: SP80-3280 and IAC91-1099, which have, respectively, susceptibility, and intermediate resistance to D. saccharalis. Si was applied in soil in an equivalent rate of 800 kg of Si ha−1. Before herbivory, Si increased stalk diameter and plant height in both varieties, and number of leaves and leaf width were only increased in IAC91-1099. After 20 days of herbivory, Si increased stalk diameter in both varieties and plant height in IAC91-1099, but decreased the number of leaves and leaf width in SP80-3280. Larval D. saccharalis showed a reduced weight and a greater index for mandible abrasion after feeding Si-treated plants independently of variety. No influence of Si-treated plants was found in immunological parameters of larvae (total number of hemocytes, cell viability, encapsulation capability, lysozyme active). The activity of phenol oxidase, an immunological and stress marker for insects, was greater in larval D. saccharalis fed with IAC 91-1099, independently of Si. In conclusion, Si application improved sugarcane growth of IAC91-1099 and impaired the development of larval D. saccharalis in both sugarcane varieties.

Reshi Z.A., Ahmad W., Lukatkin A.S., Javed S.B.

Secondary metabolites are gaining an increasing importance in various industries, such as pharmaceuticals, dyes, and food, as is the need for reliable and efficient methods of procuring these compounds. To develop sustainable and cost-effective approaches, a comprehensive understanding of the biosynthetic pathways and the factors influencing secondary metabolite production is essential. These compounds are a unique type of natural product which recognizes the oxidative damage caused by stresses, thereby activating the defence mechanism in plants. Various methods have been developed to enhance the production of secondary metabolites in plants. The elicitor-induced in vitro culture technique is considered an efficient tool for studying and improving the production of secondary metabolites in plants. In the present review, we have documented various biosynthetic pathways and the role of secondary metabolites under diverse environmental stresses. Furthermore, a practical strategy for obtaining consistent and abundant secondary metabolite production via various elicitation agents used in culturing techniques is also mentioned. By elucidating the intricate interplay of regulatory factors, this review paves the way for future advancements in sustainable and efficient production methods for high-value secondary metabolites.

Otolakoski M.G., Bagio B.Z., Viegas B.G., Milan C.S., Huzar‐Novakowiski J.

AbstractSilicon can increase the natural defence of plants against stresses including herbivorous insects. Silicon dioxide (SiO2) is one of the forms of silicon, and despite its wide use in the industrial sector, its use in agriculture is still poorly adopted. The aim of this study was to evaluate the effectiveness of foliar application of SiO2 in inducing defence against Spodoptera frugiperda in soybean. The experiments were conducted in a completely randomised design with four treatments (0%, 1%, 2.5%, and 5% of SiO2). The effect on cannibalism, biological parameters (mortality, duration of the larval stage, duration of the pupal stage and pupal weight) and wear on the mandible of S. frugiperda were evaluated. The foliar silicon content was also determined. The supply of SiO2 prolonged the duration of the larval and pupal stages of the S. frugiperda by 0.56 and 0.17 days for each 1% of SiO2 applied, respectively. The use of SiO2 at 5% increased the mortality rate of caterpillars in the larval stage by approximately 25%. There was no effect of SiO2 application on cannibalism and weight of S. frugiperda pupae. There was wear on the caterpillars' jaws in the third and fourth instar at the highest SiO2 concentration. The application of SiO2 promoted greater accumulation of silicon in soybean leaves. It is concluded that the foliar application of SiO2 affects the biological performance of S. frugiperda through the induction of defence in the soybean crop and presents itself as a promising strategy in integrated pest management programmes.

Priya, Kumar R., Bhatt R., Kashyap L., Shera P.S.

Sugarcane is a long duration important cash crop in India which is harvest after 10–18 months. Amongst various biotic and abiotic stressors affecting sugarcane, sugarcane stalk borer Chilo auricilius causes huge economic losses in yield and quality parameters. No synthetic chemical is effective against stalk borer due to its internally feeder habitat. Therefore, one ecologically sound best management practice in sugarcane is application of silicon to mitigate against stalk borer. Various sources of silicon viz. T1, T2, T3 and T4 were of silicon material (SM) 50% @ 8, 10, 12 and 15 kg/acre, respectively; T5 and T6 were of rice husk ash (RHA) @ 200 and 400 kg/acre; T7 and T8 were of bagasse ash (BA) @ 200 and 400 kg/acre; T9 Trichogramma chilonis @ 20,000 eggs per card (12 releases) and T10 untreated control were evaluated for retention in soil, plant and impact on stalk borer, cane yield and quality traits in sugarcane cultivar CoPb 98. In soil, silicon persistence decreased over the time in T4 at 0 (209.82 ± 1.28 mg kg−1) and 300 days after planting (DAP) (126.94 ± 4.49 mg kg−1), respectively. In sugarcane stalks, the uptake of silicon increased over days (T4) 1.84 ± 0.07 and 2.50 ± 0.32 mg kg−1 at 0 and 300 DAP, respectively. Stalk borer incidence (%) reduced significantly in T4 (12.89 ± 0.77%) compared to control (21.33 ± 1.33%) (p ≤ 0.000). Cane traits viz. cane length, per cent germination, number of millable cane/clump, single cane weight, yield increased significantly with the application of silicon. Juice quality traits such as Brix, Sucrose, Commercial cane sugar, CCS and CCS %, were also enhanced significantly in CoPb 98. As observed in the scanning electron microscope (SEM), third instar stalk borer larvae on the Si+ stalks eroded their mandibles with feeding on silicon enriched tissues. The cost-benefit ratio showed that among the SM the highest B:C ratio 1.74 in (T4) SM 50% @ 15 kg/acre was at par 1:73 with 12 kg/acre (T3) in terms of reducing stalk borer infestation and significantly increase cane yield and quality traits. Therefore, SM 50% @ 12 kg/acre can be used for the management of stalk borer and also be vibrant part of integrated pest management in sugarcane crop.

Veeran Sivakumar I., Periyakaman C., Peyandi Paraman M., Jayachandran J.

AbstractSilicon (Si) can improve plant resistance to herbivorous insect attack. Early shoot borer (ESB), is one of the most solemn lepidopterans borers on sugarcane in India. Even with insecticide application, management of this pest is difficult. The management requires a fresh new approach. As a result, the current study aims to determine the effect of silicon on the early shoot borer, Chilo infuscatellus Walker, through biophysical factor analysis and mandibular wear documentation. When sugarcane leaves were treated with calcium silicate at 1000 kg/ha, scanning electron microscopy revealed the presence of silicified cells and trichomes, as well as increased cell wall thickness, silicon content, and waxes content. Furthermore, larvae of an early shoot borer fed silica-treated plants showed a complete wearing of mandibles as compared to untreated check.

Sun W., Su Q., Yang W., Zhou J., Gao Y.

Third-generation oriental armyworm larvae, Mythimna separata (Walker) (Lepidoptera: Noctuidae), have caused considerable economic losses in Jilin. Understanding the occurrence, regularity and return movement of third-generation adults is crucial for pest forecasting. The study was conducted using systemic monitoring, radar observations and molecular markers from 2015 to 2019. The main results are as follows: (1) third-generation moths were regularly captured from late August to late September. These moths have been attributed to local emergence and were identified as an “emigration population.” Wind speed and temperature were advantageous for moth migration, and advantageous northeasterly winds account for 9.6% of the total. Radar studies determined that the migrant flying height was mainly below 600 m. Moths migrated over a range of directions, including their return movements. Forward trajectories predicted that the destination regions of the Korean Peninsula, the Russian Far East, and northern China were unfavorable for survival. (2) A total of 29 haplotypes were detected. There were unique haplotypes between two sampling years. The haplotype analysis indicated similar content in the two sampling years. The haplotype diversity indices appear to have been maintained. Overall, our findings indicate that the moths did not make a successful return flight, but the genetic diversity was unaffected.

Islam T., Moore B.D., Johnson S.N.

Herbivorous insects have evolved various anti-predator defences, including morphological, behavioural, and immune defences, which can make biocontrol of herbivorous pests challenging. Silicon (Si) accumulation in plants is a potent physical defence against mandibulate insects. However, it remains uncertain how Si affects the anti-predator defences of insect herbivores and plant defences following herbivory. We grew the model grass, Brachypodium distachyon, hydroponically with (+Si) or without (–Si) Si and investigated the plant-mediated effects of Si on the anti-predator defences of the cotton bollworm, Helicoverpa armigera, integrating morphological (i.e. integument resistance and thickness), behavioural, and immune defences. We also examined the effects of Si on plant compensatory growth and leaf trichome production. Larval growth, leaf consumption, and integument resistance were lower when feeding on +Si plants compared to when feeding on –Si plants. Larval integument thickness, defensive behaviours, haemocyte density, and lysozyme-like activity in the haemolymph were unaffected by Si. Larvae fed on +Si plants had higher haemolymph phenoloxidase (PO) and total-PO activities than larvae fed on –Si plants, although this did not enhance the melanisation response of larvae. Furthermore, Si supplies increased plant compensation for herbivory and constitutive trichome production, whereas herbivory induced trichome production only on –Si plants. We provide the first evidence for plant-mediated effects of Si on anti-predator defences of an insect herbivore. We suggest that the lower integument resistance of larvae when feeding on Si-supplemented plants could contribute to their vulnerability to natural enemies and that high PO activity may impose fitness costs (e.g. delayed development).

Waterman J.M., Cibils‐Stewart X., Cazzonelli C.I., Hartley S.E., Johnson S.N.

Silicon (Si) can adversely affect insect herbivores, particularly in plants that evolved the ability to accumulate large quantities of Si. Very rapid herbivore-induced accumulation of Si has recently been demonstrated, but the level of protection against herbivory this affords plants remains unknown. Brachypodium distachyon, a model Si hyperaccumulating grass, was exposed to the chewing herbivore, Helicoverpa armigera, and grown under three conditions: supplied Si over 34 d (+Si), not supplied Si (−Si), or supplied Si once herbivory began (−Si → +Si). We evaluated the effectiveness of each Si treatment at reducing herbivore performance and measured Si-based defenses and phenolics (another form of defense often reduced by Si). Although Si concentrations remained lower, within 72 h of exposure to Si, −Si → +Si plants were as resistant to herbivory as +Si plants. Both +Si and −Si → +Si treatments reduced herbivore damage and growth, and increased mandible wear compared to −Si. After 6 h, herbivory increased filled Si cell density in −Si → +Si plants, and within 24 h, −Si → +Si plants reached similar filled Si cell densities to +Si plants, although decreased phenolics only occurred in +Si plants. We demonstrate that plants with short-term Si exposure can rapidly accumulate Si-based antiherbivore defenses as effectively as plants with long-term exposure.

Pereira P., Nascimento A.M., de Souza B.H., Peñaflor M.F.

Supplementation with Silicon (Si) is well-known for increasing resistance of grasses to insect herbivores. Although the exact underlying mechanism remains unknown, Si accumulation interacts with the jasmonic acid-signalling pathway, which modulates herbivore-induced plant defences. We examined whether Si supplementation alters direct and induced indirect defences in maize plants in ways that deter the initial infestation by the fall armyworm Spodoptera frugiperda (JE Smith). We assessed the herbivore’s oviposition preference, neonate and third-instar larval performance as well as the recruitment of a predator of young larvae, the flower bug Orius insidiosus (Say), by herbivore-induced plant volatiles (HIPVs). In choice tests, S. frugiperda deposited about two times more eggs on −Si than on +Si maize. The mortality of neonate S. frugiperda larvae was about sixfold higher in +Si compared to −Si plants, even though they consumed similar leaf area on both treatments. Although there were no mortality differences, Si supplementation also impacted third-instar larvae that gained about twofold less weight than those fed on −Si maize. In olfactometer assays, O. insidiosus was not attracted to volatiles of uninfested maize plants with or without Si supplementation, but it was attracted to those emitted by fall armyworm-infested plants, irrespective of whether plants received Si supplementation. However, when the flower bug could choose between the volatiles released from −Si and +Si fall armyworm-infested plants, it preferentially oriented to +Si fall armyworm-infested plant. Our results show that Si supplementation in maize may deter fall armyworm colonization because of greater direct defences and attractiveness of HIPVs to the flower bug.

Li H., Liu F., Fu L., Liu Z., Zhang W., Wang Q., Rao X.

Insect C-type lectins (CTLs) play vital roles in modulating humoral and cellular immune responses. The oriental armyworm, Mythimna separata (Walker) (Lepidoptera: Noctuidae) is a migratory pest that causes significant economic loss in agriculture. CTLs have not yet been systematically identified in M. separata. In this study, we first constructed a transcriptome of M. separata larvae, generating a total of 45,888 unigenes with an average length of 910 bp. Unigenes were functionally annotated in six databases: NR, GO, KEGG, Pfam, eggNOG, and Swiss-Prot. Unigenes were enriched in functional pathways, such as those of signal transduction, endocrine system, cellular community, and immune system. Thirty-five unigenes encoding C-type lectins were identified, including CTL-S1~CTL-S6 (single CRD) and IML-1~IML-29 (dual CRD). Phylogenetic analyses showed dramatic lineage-specific expansions of IMLs. Sequence alignment and structural modeling identified potential ligand-interacting residues. Real-time qPCR revealed that CTL-Ss mainly express in eggs and early stage larvae, while IMLs mainly express in mid-late-stage larvae, pupae, and adults. In naïve larvae, hemocytes, fat body, and epidermis are the major tissues that express CTLs. In larvae challenged by Escherichia coli, Staphylococcus aureus, or Beauveria bassiana, the expression of different CTLs was stimulated in hemocytes, fat body and midgut. The present study will help further explore functions of M. separata CTLs.

Acevedo F.E., Peiffer M., Ray S., Tan C., Felton G.W.

Silicon (Si) is a beneficial mineral that enhances plant protection against abiotic and biotic stresses, including insect herbivores. Si increases mechanical and biochemical defenses in a variety of plant species. However, the use of Si in agriculture remains poorly adopted despite its widely documented benefits in plant health. In this study, we tested the effect of Si supplementation on the induction of plant resistance against a chewing herbivore in crops with differential ability to accumulate this element. Our model system comprised the generalist herbivore fall armyworm (FAW) Spodoptera frugiperda and three economically important plant species with differential ability to uptake silicon: tomato (non-Si accumulator), soybean, and maize (Si-accumulators). We investigated the effects of Si supply and insect herbivory on the induction of physical and biochemical plant defenses, and herbivore growth using potted plants in greenhouse conditions. Herbivory and Si supply increased peroxidase (POX) activity and trichome density in tomato, and the concentration of phenolics in soybean. Si supplementation increased leaf Si concentration in all plants. Previous herbivory affected FAW larval weight gain in all plants tested, and the Si treatment further reduced weight gain of larvae fed on Si accumulator plants. Notably, our results strongly suggest that non-glandular trichomes are important reservoirs of Si in maize and may increase plant resistance to chewing herbivores. We conclude that Si offers transient resistance to FAW in soybean, and a more lasting resistance in maize. Si supply is a promising strategy in management programs of chewing herbivores in Si-accumulator plants.

Abbasi A., Sufyan M., Arif M.J., Sahi S.T.

The current experiment was conducted in greenhouse conditions to check the effect of silicon application methods (foliar and drenching), silicon sources (silicon dioxide: SiO2 and potassium silicat...

Koyama J., Matsumura M.

Mir S.H., Rashid I., Hussain B., Reshi Z.A., Assad R., Sofi I.A.

The theory of co-evolution suggests that herbivores play an important role in the diversification and composition of plant communities. A prevalent idea holds that grasses and grazing animals participated in an evolutionary ‘arms race’ as grassland ecosystems started spreading across the continents. In this race, besides other things, silicification in the form of phytoliths occurred in the grasses, and the graminivorous herbivores responded through specialized mandibles to feed on plants rich in phytoliths. It is important to understand whether these mandibles equip the herbivores in different environments or the grasses can augment their defense by channelizing their energy in high resource milieu. Here we used rescuegrass (Bromus catharticus; Family: Poaceae), an alien species of South America, to understand the mechanism of resistance offered by this species against a local insect herbivore (Oxya grandis; Family: Acrididae), graminivorous grasshopper, in different silicon rich environments. We used different concentrations of silicon and observed the types of phytoliths formed after Si amendments and studied the effect of phytoliths on mandible wear of the grasshopper. Silicon concentrations increased ca. 12 fold in the highest supplementation treatments. The results reveal that higher foliar silica concentration in Si rich plants did not result in changing the morphology of the phytoliths, still the leaf tissue consumption was lower in higher Si treatments, perhaps due to mandibular wear of the grasshoppers. The study opens a new dimension of investigating the role of Si amendments in reducing herbivory.