Exigua Larvae Research Articles

Coupling Transcriptomics and Behaviour to Unveil the Olfactory System of Spodoptera exigua Larvae.

Insect chemosensation is crucial for many aspects related to food seeking, enemy avoidance, and reproduction. Different families of receptors and binding proteins interact with chemical stimuli, including odorant receptors (ORs), ionotropic receptors (IRs), gustatory receptors (GRs), odorant binding proteins (OBPs) and chemosensory proteins (CSPs). In this work, we describe the chemosensory-related gene repertoire of the worldwide pest Spodoptera exigua (Lepidoptera: Noctuidae), focusing on the transcripts expressed in larvae, which feed on many horticultural crops producing yield losses. A comprehensive de novo assembly that includes reads from chemosensory organs of larvae and adults, and other larval tissues, enabled us to annotate 200 candidate chemosensory-related genes encoding 63 ORs, 28 IRs, 38 GRs, 48 OBPs and 23 CSPs. Of them, 51 transcripts are new annotations. Fifty ORs are expressed in larval heads based on RNA-seq and reverse transcription PCR analyses. Fourteen OBPs are expressed in larval, but not in adult heads. We also observe that expression profiles of ORs are strongly and non-specifically up-regulated upon pre-exposure of larvae to single volatile organic compounds (VOCs). Finally, we develop a behavioural assay to study the attraction/repellence to VOCs in S. exigua larvae and thus identify candidate ecologically relevant odours. A single-dose assay demonstrated that 1-hexanol triggers attraction and indole repels larvae at any timepoint. This work establishes the foundation for the study of chemosensation in S. exigua larvae, allowing further studies aimed to characterize chemosensory-related genes that underlie the ecologically relevant behaviours of larvae.

The Role of Chrysoperla carnea (Steph.) (Neuroptera: Chrysopidae) as a Potential Dispersive Agent of Noctuid Baculoviruses.

Simple SummaryBaculoviruses (BV) infect several lepidopteran pests of economic importance, such as the beet armyworm Spodoptera exigua. The joint use of microbiological and macrobiological strategies may improve the efficacy of control. Laboratory bioassays were developed to evaluate the interactions between two BVs: the multiple nucleopolyhedroviruses of S. exigua (SeMNPV) and Autographa californica (AcMNPV), and the predator Chrysoperla carnea. The excretion products of the predator’s larvae (drops) and adults (meconia) were microscopically examined after the ingestion of BV-infected S. exigua larvae. For both types of excreta and BVs, viral occlusion bodies (OBs) (resistance forms) were observed. These OBs were infective to healthy S. exigua larvae when applied in water suspension and in direct deposition. The virulence of meconia was higher in suspensions (higher viral load), while larval drops were more virulent in direct application due to their liquid nature and their easiness of consumption. The fitness of C. carnea was slightly affected by the consumption of both BV-infected prey. No preference was shown between healthy and BV-infected S. exigua, and both were preferred vs. the aphid Macrosiphum euphorbiae. Our findings present C. carnea, and particularly its larvae, as a promissory candidate for BV dispersion in the field.Baculoviruses (BV) are highly effective against lepidopteran pests of economic importance such as Spodoptera exigua. The combined use of entomopathogens and macrobiological control agents requires the study of their relationships. Laboratory bioassays were developed to evaluate the interactions between the multiple nucleopolyhedroviruses of S. exigua (SeMNPV) and Autographa californica (AcMNPV), and the predator Chrysoperla carnea. The microscopic examination of predator’s excreta (larval drops and meconia) after the ingestion of BV-infected S. exigua revealed the presence of viral occlusion bodies (OBs). The reinfection of S. exigua larvae with BVs-contaminated excreta by using OBs water suspensions or by direct application both yielded high mortality values but different speed-of-kill results. Meconia killed before in suspensions due to their higher viral load and larval excretion drops did so in direct application due to their liquid nature and their easiness of consumption. The prey-mediated ingestion of SeMNPV and AcMNPV triggered slight effects in C. carnea, which were probably derived from the food nutritional quality. Chrysoperla carnea larvae did not discriminate between healthy and BV-infected S. exigua, while a preference was shown for S. exigua (healthy or infected) vs. Macrosiphum euphorbiae. Our findings present C. carnea, and particularly its larvae, as a promissory candidate for BV dispersion in the field.

Broflanilide effectively controls Helicoverpa armigera and Spodoptera exigua exhibiting diverse susceptibilities to chlorantraniliprole and emamectin benzoate.

The cotton bollworm, Helicoverpa armigera (Hübner), and the beet armyworm, Spodoptera exigua (Hübner), are two major polyphagous lepidopteran pests of cultivated crops. They develop various levels of resistance to many frequently applied broad-spectrum insecticides. Here, the larval susceptibilities of a laboratory population and six field-collected populations per pest from Hunan Province, China to three insecticides were determined using a standard leaf-dipping method in the laboratory. Field-plot trials were conducted to verify the control efficacies of broflanilide 100 g L-1 suspension concentrate (SC), chlorantraniliprole 5% SC and emamectin benzoate 5.7% water-dispersible granule, against H. armigera and S. exigua larvae using foliar sprays in 2013 and 2019. Variations among H. armigera and S. exigua field populations in their susceptibility levels to the three insecticides were observed in Linli, Yueyang and Changsha counties from 2013 to 2019. They were still high susceptibility to broflanilide only, but developed low and/or moderate levels of resistance to chlorantraniliprole and emamectin benzoate. In addition, broflanilide at 25 g ha-1 provided an excellent control efficacy of 81.92% to 96.46% against these pests during the 3-14-days period after treatment in both years, whereas chlorantraniliprole at 50 g ha-1 and emamectin benzoate at 4.5 g ha-1 exhibited significantly decreased efficacies, which were consistent with their corresponding toxicity levels. These results suggest that broflanilide should be an important new tool for the effective control of diamide- and avermectin-resistant H. armigera and S. exigua. © 2020 Society of Chemical Industry.

Botanical extracts from Dodonaea viscosa (Sapindales: Sapindaceae) reduce hemocyte counts from Spodoptera exigua (Lepidoptera: Noctuidae) with potential insecticidal synergism with Isaria fumosorosea (Hypocreales: Cordycipitaceae)

ABSTRACT Some botanical extracts affect the cellular immune system of insects by interfering with normal hemocyte function. This gives rise to diminution in cellular immunity and causes a decrease in insect defense. This investigation evaluated the effect of acetonic (AcEDv) and methanolic (MeEDv) extracts of Dodonaea viscosa (1000, 2000, and 4000 ppm) on the total hemocyte count (THC) present in the hemolymph of Spodoptera exigua, as well as on its insecticidal activity, on its own and in combination with the entomopathogenic fungus Isaria fumosorosea. Water and Tween® were used as negative controls and Lorsban® as a positive control. Second instar S. exigua larvae were separately fed an artificial diet incorporating both extracts. THC was significantly lower in AcEDv treatment at 1000 ppm and MeEDv treatment at 1000 and 4000 ppm compared with negative controls. The insecticidal action of the individual extracts and those in combination with the conidia of I. fumosorosea manifested from day 21, while at day 28, the AcEDv at 1000 and 2000 ppm and the MeEDv at 4000 ppm applied with the fungus revealed mortality percentages higher than 50% and a significantly higher mortality compared with the negative controls. In conclusion, the extracts of D. viscosa reduced the total THC of S. exigua and suggest that the application of this plant extract presents a synergistic effect on the mortality of S. exigua exposed to entomopathogenic fungus I. fumosorosea.

The response of sycanus aurantiacus ishikawa et okajima (hemiptera: reduviidae) to color polymorphisms larvae of spodoptera exigua (hubner) (lepidoptera: noctuidae)

his study aims to evaluate the predatory behavior, preference and functional response of S. aurantiacus in color polymorphism larvae of S. exigua. The predatory behavior and preference test of S. aurantiacus using green and dark brown color larvae of S. exigua. Functional response test was carried out with 5 treatments of larvae population density with 10 replications. The results showed that S. aurantiacus prefers to dark brown larvae of S. exigua than green. The time taken by predators to find the first and subsequent prey was faster in dark brown larvae than in green, both on low or high larval density. The search time for the first prey on dark brown larvae was 22.7 minutes (at high density) and 39.3 minutes (at low density) while those on green larvae were 26.5 minutes and 42.7 minutes. S. aurantiacus showed type-II functional response to the density rate of S. exigua larvae both dark brown and green with the line equation respectively Y = 1,284x / 1 + 0,056x; R2: 0.96; a: 0,107; Th: 0.52 (dark brown larvae) Y = 1.32x / 1 + 0.063x; R²: 0.952; a: 0,109; Th: 0.58 (green larvae).

Contrasting susceptibility of lepidopteran pests to diamide and pyrethroid insecticides in a region of overwintering and migratory intersection.

Pesticide resistance is a growing issue worldwide, and susceptibility of pest populations should be monitored in migratory intersection regions for successful resistance management. We determined the susceptibility of eight noctuid species from the Florida Panhandle to bifenthrin (pyrethroid) and chlorantraniliprole (diamide). Larvae from field and laboratory populations were exposed to commercial insecticide formulations using the leaf-dip method in concentration-mortality bioassays. The field populations of Helicoverpa zea (Boddie), Spodoptera frugiperda (Smith), S. eridania (Stoll), S. exigua (Hubner) and Chloridea virescens (Fabricius) had reduced susceptibility to bifenthrin compared with the laboratory populations. Resistance ratios to bifenthrin were as high as 10 071-fold in S. exigua and 436-fold in S. frugiperda, while there was no reduced susceptibility in Agrotis ipsilon (Hufnagel). The susceptibility to chlorantraniliprole was similar between the field and laboratory populations studied, except for S. exigua that exhibited 630-fold resistance to the diamide. The probit regression equations indicated that the larval mortality of S. exigua and S. frugiperda populations was <80% with bifenthrin at the concentration equivalent to the label rate. Likewise, the estimated mortality of S. exigua larvae with chlorantraniliprole at the label rate concentration was <80%. The lepidopteran pest populations tested were variable in susceptibility to bifenthrin by contrast to more consistent susceptibility to chlorantraniliprole. These results help in the choice of effective insecticides for integrated pest management and resistance management in cropping systems colonized by migratory lepidopteran pests from the U.S. Gulf Coast region. © 2020 Society of Chemical Industry.

Immunosuppressive Activities of Novel PLA2 Inhibitors from Xenorhabdus hominickii, an Entomopathogenic Bacterium.

Simple SummaryInsect immune responses defend fatal attacks from entomopathogens. A Gram-negative Xenorhabdus hominickii exhibits high entomopathogenicity against lepidopteran insects. During the pathogenic processes, the bacteria suppress host insect immune responses by inhibiting phospholipase A2 (PLA2) enzyme activity with the bacterial secondary metabolites. PLA2 catalyzes eicosanoid biosynthesis. Eicosanoids mediate both cellular and humoral immune responses against various insect pathogens. This study identified eight different PLA2 inhibitors from the bacterial culture broth. Butanol extract of the culture broth possessed high potency to inhibit PLA2 activity. Subsequent fractionations led to identification of eight different compounds. The synthetic compounds also showed PLA2 inhibition and insecticidal activities. Furthermore, the addition of the bacterial PLA2 inhibitors significantly enhance other bacterial pathogenicity, suggesting its potential to be applied for developing novel insecticides. Eicosanoids mediate both cellular and humoral immune responses in insects. Phospholipase A2 (PLA2) catalyzes the first committed step in eicosanoid biosynthesis. It is a common pathogenic target of two entomopathogenic bacteria, Xenorhabdus and Photorhabdus. The objective of this study was to identify novel PLA2 inhibitors from X. hominickii and determine their immunosuppressive activities. To identify novel PLA2 inhibitors, stepwise fractionation of X. hominickii culture broth and subsequent enzyme assays were performed. Eight purified fractions of bacterial metabolites were obtained. Gas chromatography and mass spectrometry (GC-MS) analysis predicted that the main components in these eight fractions were 2-cyanobenzoic acid, dibutylamine, 2-ethyl 1-hexanol, phthalimide (PM), dioctyl terephthalate, docosane, bis (2-ethylhexyl) phthalate, and 3-ethoxy-4-methoxyphenol (EMP). Their synthetic compounds inhibited the activity of PLA2 in hemocytes of a lepidopteran insect, Spodoptera exigua, in a dose-dependent manner. They also showed significant inhibitory activities against immune responses such as prophenoloxidase activation and hemocytic nodulation of S. exigua larvae, with PM and EMP exhibiting the most potent inhibitory activities. These immunosuppressive activities were specific through PLA2 inhibition because an addition of arachidonic acid, a catalytic product of PLA2, significantly rescued such suppressed immune responses. The two most potent compounds (PM and EMP) showed significant insecticidal activities after oral administration. When the compounds were mixed with Bacillus thuringiensis (Bt), they markedly increased Bt pathogenicity. This study identified eight PLA2 inhibitors from bacterial metabolites of X. hominickii and demonstrated their potential as novel insecticides.

UTILIZATION OF PAPAYA LEAVES (Carica papaya L.) TO CONTROL ONION PEST SPODOPTERA EXIGUA (LEPIDOPTERA: NOCTUIDAE)LEPIDOPTERA (NOCTUIDAE)

Spodoptera exigua is a migrant pest that attacks onions simultaneously in groups. The utilization of papaya leaves to control pests due to papaya leaves have toxic compounds that can kill pests. This study aims to measure the ability of papaya leaves to control S. exigua larvae. This research was conducted using a completely randomized design (CRD) experimental method with two treatment factors. The first factor was papaya leaf concentration (0 g / l, 30 g / l, 70 g / l, 100 g / l, 120 g / l), and the second factor is a mixture of kerosene. The treatment was repeated three times. The study was conducted at the Agrotechnology Laboratory, Agriculture Faculty Muhammadiyah University, South Tapanuli. The results showed that papaya leaves could kill S. exigua larvae. The highest mortality of S. exigua worms There were statistically significant non-treatments among treatments.

Toxicity of Phenylpropanoids from Alpinia galanga (Zingiberaceae) extracts against Spodoptera exigua Hübner (Lepidoptera: Noctuidae)

Spodoptera exigua Hubner is one of the most important agricultural pests in Thailand. The present study investigated the toxicity of crude extracts and phenylpropanoid compounds of A. galanga (Zingiberaceae) against S. exigua. After 24 h of a topical application bioassay on secondary instar larvae, the ethyl acetate extract estimation of the LD50 of A. galanga (Zingiberaceae) showed toxicity toward secondary instar S. exigua larvae (LD50 ~ 2.44 µg/larva). Phenylpropanoid compounds were isolated from the ethyl acetate A. galanga crude extract which has [1’S]-1’-acetoxychavicol acetate as highest toxicity (LD50 of 1.93 µg/larvae). [1’S]-1’-acetoxychavicol acetate also showed carboxylesterase activity inhibition. Thus, the ethyl acetate extract of A. galanga may have [1’S]-1’-acetoxychavicol acetate as an active ingredient for controlling this pest, which could be used as an alternative to application of environmentally insecticides for controlling S. exigua.

Antagonistic Effect of Truncated Fragments of Bacillus thuringiensis Vip3Aa on the Larvicidal Activity of its Full-length Protein.

Vip3Aa is a vegetative insecticidal protein produced by Bacillus thuringiensis. The protein is produced as an 88-kDa protoxin that could be processed by insect gut proteases into a 22-kDa N-terminal and a 66-kDa C-terminal fragments. The C-terminal part could bind to a specific receptor while the N-terminal part is required for toxicity and structural stability. To demonstrate the antagonistic effect of truncated fragments on the insecticidal activity of the full-length Vip3Aa. The full-length protein (Vip3Aa), a 66-kDa C-terminal fragment (Vip3Aa-D199) and a predicted carbohydrate binding module (CBM) were produced in Escherichia coli. Purified proteins were mixed at different ratios and fed to Spodoptera litura and Spodoptera exigua larvae. Mortality was recorded and compared between larvae fed with individual toxin and mixtures of the full-length and truncated toxins. Production level of the Vip3Aa-D199 was significantly decreased comparing to that of the full-length protein. Vip3Aa-D199 and CBM fragment were not toxic to insect larvae whereas Vip3Aa showed high toxicity with LC50 about 200 ng/cm2. Feeding the larvae with mixtures of the Vip3Aa and Vip3Aa-D199 at different ratios revealed antagonistic effect of the Vip3Aa-D199 on the toxicity of Vip3Aa. Results showed that the lethal time (LT 50 and LT 95) of larvae fed the mixture toxins was longer than those fed the Vip3Aa alone. In addition, a CBM fragment could inhibit toxicity of the full-length Vip3Aa. Our results demonstrated that the Vip3Aa-D199 and a CBM fragment could complete for the membrane binding thus rendering activity of the full-length Vip3Aa.

Deletion mutant of PGE2 receptor using CRISPR-Cas9 exhibits larval immunosuppression and adult infertility in a lepidopteran insect, Spodoptera exigua

Prostaglandins (PGs) mediate various physiological processes in insects and other invertebrates, but there is very little information on PG receptors. This study identified a PGE2 receptor (SePGE2R) in the lepidopteran insect, Spodoptera exigua, and addressed its functional association with cellular immunity, development, and reproduction. SePGE2R is expressed in most developmental stages and tissues. After SePGR2R expression knock down by RNA interference (RNAi), larval nodule formation (clears bacterial infections from circulating hemolymph) was severely suppressed coupled with reduced F-actin growth in hemocytes. Treating female adults with RNAi prevented nurse cell dumping in follicles and interfered with oocyte development. SePGE2R was heterologously expressed in Sf9 cells, in which the endogenous S. frugiperda PGE2R was knocked down by small interfering RNA. This transiently expressed SePGE2R responded to PGE2, but not other PGs, with dose-dependent up-regulation of intracellular cAMP concentrations. Treating S. exigua larvae with PGE2 led to activation of a trimeric Gαs subunit, protein kinase A (PKA), and Rho family small intracellular G proteins in hemocytes. A deletion mutant of SePGE2R was generated using CRISPR/Cas9 which exhibited severely retarded larval development and adult reproduction. We infer that PGE2R mediates insect immune and reproductive processes via a PKA signal pathway.

Benzylideneacetone and other phenylethylamide bacterial metabolites induce apoptosis to kill insects

Xenorhabdus and Photorhabdus are entomopathogenic bacteria that can induce immunosuppression against target insects by suppressing eicosanoid biosynthesis, leading to fatal septicemia. These bacteria can synthesize and release secondary metabolites such as benzylideneacetone (BZA) and other phenylethylamide compounds that can inhibit phospholipase A2 (PLA2) and shut down eicosanoid biosynthesis. However, insecticidal activities of these bacterial metabolites remain unclear. Thus, the objective of this study was to assess cytotoxicities of BZA and seven other bacterial metabolites to insect cells. These eight bacterial metabolites exhibited significant cytotoxicities against an insect cell line Sf9 at micromolar range. Especially, BZA and cPY were highly potent at low micromolar range. When these eight bacterial metabolites were injected to hemocoels of Spodoptera exigua larvae, they significantly decreased total count of hemocytes. In Sf9 cell line and hemocytes, these bacterial metabolites induced cell membrane blebbings, apoptotic vesicles, and genomic DNA fragmentation. Terminal deoxyribonucleotidyl transferase nick end translation assay showed that these bacterial metabolites caused significant DNA breakages in cells in a dose-dependent manner. However, a pan caspase inhibitor treatment significantly rescued the cell death induced by these bacterial metabolites. Cytotoxicities of these bacterial metabolites were highly correlated with their insecticidal activities. These results indicate that the insecticidal activities of the bacterial metabolites may be induced by their apoptotic activities against hemocytes and other insect cells. Taken together, these results suggest that phenylethylamide compounds might have potential as novel insecticides.

Midgut de novo transcriptome analysis and gene expression profiling of Spodoptera exigua larvae exposed with sublethal concentrations of Cry1Ca protein.

Spodoptera exigua (Hübner) is a polyphagous pest on agricultural crops, whose control is based mainly on the application of chemical insecticides. Bacillus thuringiensis (Bt) is one of the most important biological agents that have been successfully applied as a biological control, and Cry1Ca protein is considered to be active against S. exigua. Therefore, to understand the response of S. exigua to Cry1Ca protein, high-throughput sequencing was used to analyse the S. exigua larval midgut after treatment with sublethal concentrations of Cry1Ca protein. Transcriptome data showed that a total of 98,571 unigenes with an N50 value of 1135bp and a mean length of 653bp were obtained. Furthermore, 2962 differentially expressed genes (DEGs) were identified after Cry1Ca challenge, including 1508 up-regulated and 1454 down-regulated unigenes. Among these DEGs, detoxification (CYP, CarE, and GST) and Bt resistance (ALP, APN, and ABC transporter)-related genes were differentially expressed in the midgut of S. exigua after Cry1Ca treatment. However, most DEGs of protective enzymes were down-regulated, while most DEGs related with serine protease and REPAT were up-regulated. Furthermore, almost all DEGs related to the immune signaling pathway, antimicrobial protein, and lysozyme were up-regulated by Cry1Ca treatment. These results indicated that the detoxification enzyme, protective enzymes, Bt resistance-related genes, serine protease, REPAT, and the immune response might have been involved in the response of S. exigua to Cry1Ca protein. In summary, analysis of the transcriptomal expression of genes involved in Cry1Ca protein against S. exigua provided potential clues for elucidating the host response processes and defensive mechanisms underlying Cry1Ca toxicity.

DNA sequencing reveals bacterial communities in midgut and other parts of the larvae of Spodoptera exigua Hubner (Lepidoptera: Noctuidae).

Gut microbiota has been suggested as an important component of host defense. However, microbiota in other parts of the body have rarely been characterized. In our present work, we give a detailed view of the body of Spodoptera exigua larvae, the midgut with intestinal contents (MG), midgut excluding intestinal contents (PM), intestinal contents (IC) and remaining parts excluding the MG (RM), with the objective of revealing the complexity of microorganisms and comparing the biodiversity of the S. exigua larvae-associated microbiota. Our results provide the first evidence that third and fifth larvae samples of S. exigua were dominated by members of the phyla Firmicutes and Proteobacteria. In addition, there were no obvious differences in relative abundances of microbiota among MG, PM and RM at the phylum level. MG3 and MG5 (nearly RM5) harbored the richest microbial community, with much higher abundance of Halomonas, Pseudomonas and Methylobacterium, respectively. Intestinal contents contained the lowest diversity and highest abundance of Enterococcus. Knowledge of the bacteria in a major herbivorous insect, such as S. exigua, can facilitate the acquisition of special biological resources for agricultural pest control.

Wide spectrum and high frequency of genomic structural variation, including transposable elements, in large double-stranded DNA viruses.

Our knowledge of the diversity and frequency of genomic structural variation segregating in populations of large double-stranded (ds) DNA viruses is limited. Here, we sequenced the genome of a baculovirus (Autographa californica multiple nucleopolyhedrovirus [AcMNPV]) purified from beet armyworm (Spodoptera exigua) larvae at depths >195,000× using both short- (Illumina) and long-read (PacBio) technologies. Using a pipeline relying on hierarchical clustering of structural variants (SVs) detected in individual short- and long-reads by six variant callers, we identified a total of 1,141 SVs in AcMNPV, including 464 deletions, 443 inversions, 160 duplications, and 74 insertions. These variants are considered robust and unlikely to result from technical artifacts because they were independently detected in at least three long reads as well as at least three short reads. SVs are distributed along the entire AcMNPV genome and may involve large genomic regions (30,496 bp on average). We show that no less than 39.9 per cent of genomes carry at least one SV in AcMNPV populations, that the vast majority of SVs (75%) segregate at very low frequency (<0.01%) and that very few SVs persist after ten replication cycles, consistent with a negative impact of most SVs on AcMNPV fitness. Using short-read sequencing datasets, we then show that populations of two iridoviruses and one herpesvirus are also full of SVs, as they contain between 426 and 1,102 SVs carried by 52.4–80.1 per cent of genomes. Finally, AcMNPV long reads allowed us to identify 1,757 transposable elements (TEs) insertions, 895 of which are truncated and occur at one extremity of the reads. This further supports the role of baculoviruses as possible vectors of horizontal transfer of TEs. Altogether, we found that SVs, which evolve mostly under rapid dynamics of gain and loss in viral populations, represent an important feature in the biology of large dsDNA viruses.

Displaying enhancing factors on the surface of occlusion bodies improves the insecticidal efficacy of a baculovirus.

Baculoviruses provide long-lasting control of crop pests and are harmless to humans and non-target animals, making them attractive bioinsecticides. Autographa californica multiple nucleopolyhedrovirus (AcMNPV) has a wide-host range and is one such commercial bioinsecticide, but its low infectivity to older larvae and less-sensitive species precludes its large-scale application. We sought to improve the infectivity of AcMNPV. Two enhancing factors, the truncated enhancin from Agrotis segetum granulovirus and GP37 from Cydia pomonella granulovirus, were expressed in fusion with the N-terminal and middle domain of the polyhedrin envelope protein of AcMNPV. Western blotting and immunoelectron microscopy analysis indicated that the enhancing factors were expressed on the occlusion bodies of the resulting AcMNPV variants. Bioassays showed that the median lethal doses of the recombinant viruses were 3.9-fold to 7.4-fold lower than those of the wild-type virus against the second and fourth instar of Spodoptera exigua larvae. The yields of occlusion bodies from the two recombinants in S. exigua larvae were comparable with those of the wild-type virus both in vitro and in vivo. Further bioassays showed that the AcMNPV variants fusing the enhancing factors were incapable of infecting the second instar larvae of S. litura, Helicoverpa armigera, and Pyrausta nubilalis, which were not sensitive to the wild-type AcMNPV. These genetically modified AcMNPV variants exhibited an enhanced infectivity and may offer better baculovirus control of crop pests. © 2019 Society of Chemical Industry.

An influential meal: host plant dependent transcriptional variation in the beet armyworm, Spodoptera exigua (Lepidoptera: Noctuidae)

BackgroundTo understand the genetic mechanisms of insect herbivory, the transcriptional response of insects feeding on different host plant species has to be studied. Here, we generated gene expression data of the generalist herbivore Spodoptera exigua (Hübner) feeding on three selected host plant species and a control (artificial diet). The host plant species used in this study –cabbage (Brassica oleracea), maize (Zea mays) and tobacco (Nicotiana tabacum)- are members of different plant families that each employ specific defence mechanisms and toxins.ResultsSpodoptera exigua larvae had a higher growth rate, indicator for herbivore success, when feeding on Z. mays compared to larvae feeding on B. oleracea or N. tabacum. Larvae feeding on the different host plant species showed divergent transcriptional responses. We identified shared and unique gene expression patterns dependent of the host plant species the larvae fed on. Unique gene expression patterns, containing uniquely upregulated transcripts including specific detoxification genes, were found for larvae feeding on either B. oleracea or N. tabacum. No diet-specific gene cluster was identified for larvae feeding on the host for which larvae showed optimal herbivore success, Z. mays, or artificial diet. In contrast, for larvae feeding on hosts for which they showed low herbivore success, specific diet-dependent gene clusters were identified. Functional annotation of these clusters indicates that S. exigua larvae deploy particular host plant-specific genes for digestion and detoxification.ConclusionsThe lack of a host plant-specific gene activity for larvae feeding on Z. mays and the artificial diet suggest a general and non-specific gene activity for host plants with optimal herbivore success. Whereas the finding of specific gene clusters containing particular digestion and detoxifying genes expressed in larvae feeding on B. oleracea and N. tabacum, with low herbivore success, imply a host plant-specific gene activity for larvae feeding on host plants with suboptimal herbivore success. This observation leads to the conclusion that a polyphagous herbivore is able to feed on a large variation of host plants due to the flexibility and diversity of genes involved in digestion and detoxification that are deployed in response to particular host plant species.

Altering of host larval (Spodoptera exigua) calcineurin activity in response to ascovirus infection.

Calcineurin (CaN) is involved in numerous cellular processes and Ca2+ -dependent signal transduction pathways. According to our previous transcriptome studies, thousands of host larval (Spodoptera exigua) transcripts were downregulated after the infection of Heliothis virescent ascovirus 3h (HvAV-3h), while the Spodoptera exigua calcineurin genes (SeCaNs) were significantly upregulated. To understand the regulation of SeCaNs in S. exigua larvae during the infection of HvAV-3h, the functions of CaN subunit A (SeCaN-SubA) and CaN binding protein (SeCaN-BP) were analysed. The in vitro assays indicated that the bacterial expressed SeCaN-SubA is an acid phosphatase, but no phosphatase activity was detected with the purified SeCaN-BP. The transcription level of SeCaN-SubA was upregulated after HvAV-3h infection and the CaN activity was significantly increased after HvAV-3h infection in S. exigua larvae. Interestingly, the SeCaN-BP transcripts were only detectable in the HvAV-3h infected larvae. Further immunoblotting results consistently agree with those obtained by qPCR, indicating that the infection of HvAV-3h causes the upregulated expression of SeCaN-SubA and the appearance of SeCaN-BP. An interaction between the cleaved SeCaN-SubA and SeCaN-BP was detected by co-immunoprecipitation assays, and the expression of SeCaN-BP in Spodoptera frugiperda-9 (Sf9) cells can help to increase the CaN activity of SeCaN-SubA. Further investigations with CaN inhibitors suggested that HvAV-3h. Further investigations with CaN inhibitors suggested that the inhibition on host larval CaN activity can also inhibit the viral replication of HvAV-3h. The increase in CaN activity caused by HvAV-3h infection might be due to the upregulation of SeCaN-SubA and the induced expression of SeCaN-BP, and increased CaN activity is essential for ascoviral replication. © 2019 Society of Chemical Industry.

Some alternatives to the chemical control of Spodoptera exigua (Hubner, 1808) in black-eyed pea

Spodoptera exigua (Hubner), is a destructive pest in different parts of the world. In this study, the effects of indoxacarb, chlorpyrifos, deltamethrin, hexaflumuron, matrin, and Bacillus thuringiensis var. kurstaki)Bt), were evaluated against S. exigua in a complete randomized block design under field conditions. Four replications were considered for each treatment. The qualitative and quantitative damages of the pest were estimated based on plant growth characteristics. The experiments were carried out in 2016 and 2017 in a pea field in Khuzestan province, Iran. Sampling of S. exigua population was conducted 1 day before treatment (DBT) and 1, 3, 5, 7 and 10 days after treatment (DAT). The results showed that indoxacarb significantly reduced oviposition in S. exigua. Chlorpyrifos and indoxacarb significantly affected larval survival shortly after treatment. However, no significant difference was observed in larval mortality among treatments 10 DAT and all were effective against larvae. The results also showed that the maximum bean pods were observed in chlorpyrifos and indoxacarb treatments, respectively. There were the most seeds in each pod in matrin, indoxacarb, chlorpyrifos and deltamethrin treatments. According to the results, Bt and matrin were effective insecticides against S. exigua larvae and can be recommended as an alternative to chemical pesticides.

Uji Hemaglutinasi Assay pada Hemolimf Spodoptera exigua yang diberi Perlakuan Botani Pestisida

Abstract. The larval stage of the armyworm (Spodoptera exigua), has a high and polyphagous feeding activity so that these insects have the potential to be pests in agriculture. The use of botanical pesticides in this case Mirabilis jalapa, is expected to control agricultural pests so that research on the immune system of S. exigua larvae is carried out by observing lectins that play a role in analyzing foreign molecules that enter the insect's body. The results were obtained, the higher the M. jalapa concentration, at the concentration of M. jalapa 0.4% and 0.8%, the lower the hemolymf agglutination titers. This is thought to decrease the binding capacity of lectins to foreign molecules. So that M. jalapa has the potential to be used as an environmentally friendly botanical pesticide.Keywords: agricultural pests, botanical pesticides, lectin agglutination.