Cotton Bollworm Helicoverpa Armigera Research Articles

A chromosome-level haplotype-resolved genome assembly of oriental tobacco budworm (Helicoverpa assulta)

Oriental tobacco budworm (Helicoverpa assulta) and cotton bollworm (Helicoverpa armigera) are two closely related species within the genus Helicoverpa. They have similar appearances and consistent damage patterns, often leading to confusion. However, the cotton bollworm is a typical polyphagous insect, while the oriental tobacco budworm belongs to the oligophagous insects. In this study, we used Nanopore, PacBio, and Illumina platforms to sequence the genome of H. assulta and used Hifiasm to create a haplotype-resolved draft genome. The Hi-C technique helped anchor 33 primary contigs to 32 chromosomes, including two sex chromosomes, Z and W. The final primary haploid genome assembly was approximately 415.19 Mb in length. BUSCO analysis revealed a high degree of completeness, with 99.0% gene coverage in this genome assembly. The repeat sequences constituted 38.39% of the genome assembly, and we annotated 17093 protein-coding genes. The high-quality genome assembly of the oriental tobacco budworm serves as a valuable genetic resource that enhances our comprehension of how they select hosts in a complex odour environment. It will also aid in developing an effective control policy.

Investigation of the insecticidal potential of curcumin derivatives that target the Helicoverpa armigera sterol carrier protein-2

Cotton bollworm (Helicoverpa armigera) is a highly polyphagous, widely prevalent, and persistent Old World insect pest that affects numerous important crops that are directly consumed by people, including tomato, cotton, pigeon pea, chickpea, rice, sorghum, and cowpea. Insects do not synthesize steroids but obtain them from their diet. Inhibition of dietary uptake of steroids by insects is a potentially effective insecticidal mechanism that should not be toxic to humans and other mammals, who synthesize their steroids. Ten curcumin derivatives were tested against H. armigera sterol carrier protein-2 (HaSCP-2) for their potential as insecticidal agents. Curcumin derivatives were initially docked at the binding site of HaSCP-2 to determine their binding affinities and plausible binding modes. The binding modes predominantly show hydrophobic interactions of derivatives with Phe53, Phe110, and Phe89 as core interacting residues in the active site. Validation of in silico results was carried out by performing a fluorescence binding and displacement assay to determine the binding affinities of curcumin derivatives. Among a collection of curcumin derivatives tested, Cur10 showed the lowest IC50 value of 9.64 μM, while Cur07 was 19.86 μM, and Cur06 was 20.79 μM. There was a significant negative correlation between the ability of the curcumin derivatives tested to displace the fluorescent probe from the sterol binding site of HaSCP-2 and to inhibit Sf9 insect cell growth in culture, which is consistent with the curcumin derivatives acting by the novel mechanism of blocking sterol uptake. Then molecular dynamics simulation studies validated the predicted binding modes and the interactions of curcumin derivatives with HaSCP-2 protein. In conclusion, these studies support the potential use of curcumin derivatives as insecticidal agents.

Life-cycle profiling of cuticular hydrocarbons in the cotton bollworm Helicoverpa armigera (Lepidoptera: Noctuidae)

Cuticular hydrocarbons (CHCs) are the main components of the wax layer present on insects’ surface, serving as protective agents against environmental stress and/or as communication signals. It has been documented that the chemical composition of CHCs varies with species and even with developmental stage or sex of the same species. However, studies involving in a life-cycle identification of CHCs are rare. In this work, we attempted to profile the components and relative abundance of CHCs in the cotton bollworm Helicoverpa armigera at all the four developmental stages and in both sexes of pupae and adults. A total of 29 CHCs were putatively identified by gas chromatography-mass spectrometer analysis, including 14 n-alkanes, 4 methyl-branched alkenes and 11 methyl-branched alkanes, with 15 of them being detected at all the four developmental stages. Of the 29 CHCs, the straight-chain alkanes with 27, 29 and 31 carbon atoms were the major CHCs. All three classes of CHCs (n-alkanes, methyl-branched alkanes and methyl-branched alkenes) were found in both larvae and pupae, while no unsaturated hydrocarbons were observed in eggs and adults. Methyl-branched alkanes were the main component found in eggs and adults, while the composition of n-alkanes and methyl-branched alkanes in larvae and pupae varied with ages. Principal component analysis (PCA) revealed that the CHC profiles in larvae and adults changed significantly with ages, while the CHC profiles in early pupae (1-day-old) showed distinct difference from those of late pupae. Furthermore, sexual dimorphism in the CHC profile was observed in mature adults (3-day-old and 5-day-old), with male adults possessing more n-C31 and n-C33, but less 3-MeC29 than females.

Monitoring of the content and migration of heavy metals in the soils–melliferous plants–bees–beekeeping products system in biocenoses of the combat areas

Aim. To determine the specificities of perennial dynamics in the number of the main corn insect pests in different natural and climatic zones of Ukraine under climate change. Methods. The field, laboratory, mathematical methods were used. The materials of the phytosanitary entomological monitoring of the State Service of Ukraine on Food Safety and Con- sumer Protection (2005–2021) in the basic 161 enterprises in Ukraine’s regions using methodologically standardized annual registrations of the main harmful organisms of agrocenoses (Borzykh еt al, 2018). Six groups of the main corn insect pests were investigated: corn borers (Ostrinia nubilalis Hübner), wireworms (Elateridae) and false wireworms (Te- nebrionidae), cutworms (Noctuida), southern dusty surface beetle (Tanymecus dilaticollis Gyllenhal), cotton bollworm (Helicoverpa armigera Hübner), and cereal aphids (Schizaphis graminum) Rondani. The database of the Hydrometeoro- logical Center of Ukraine was used to analyze climate parameters (2005–2021). The statistical analysis of the data was conducted using MS Excel and the linear correlation-regression analysis according to Pearson, Student’s criterion was used to evaluate the reliability (probability) of the correlation coefficients. Results. The results of correlational analysis of the state of populations of the main corn insect pests demonstrated that climate change has not considerably affected the number of corn borers as well as wireworms and false wireworms in all the natural and climatic zones of Ukraine yet. A reliable moderate reverse correlation (r = –0.309) was found between the number of cutworms and the sum of effective temperatures (SET) only for the Forest-Steppe conditions – under the increase in the SET, the number of these insects was smaller. The number of the southern dusty surface beetle was in direct, reliable, moderate correlation (r = 0.335) with the SET in the Steppe, for instance, the pest responded to the increase in the SET with the rise in its number. The number of cotton bollworms in Polissia was in reliable moderate correlation (r = –0.489) with the SET. The number of cereal aphids was in a reliable moderate direct correlation (r = 0.529) with the SET in Polissia: at the increase in the SET, the number of these pests was increasing. Conclusions. Conclusions: Climate changes do not considerably affect the state of the populations of the main corn insect pests in all the natural and climatic zones of Ukraine yet: we found the correlations between the number of insect pests and the SET which did not exceed such values as weak, moderate, and conspicuous. Significant changes in the state of insect pest populations should be expected if the sum of effective temperatures during the vegetation period will considerably affect the performance and feeding qualities of the cultivated plants.

Population dynamics of corn insect pests in Ukraine under climate change

Aim. To determine the specificities of perennial dynamics in the number of the main corn insect pests in different natural and climatic zones of Ukraine under climate change. Methods. The field, laboratory, mathematical methods were used. The materials of the phytosanitary entomological monitoring of the State Service of Ukraine on Food Safety and Con- sumer Protection (2005–2021) in the basic 161 enterprises in Ukraine’s regions using methodologically standardized annual registrations of the main harmful organisms of agrocenoses (Borzykh еt al, 2018). Six groups of the main corn insect pests were investigated: corn borers (Ostrinia nubilalis Hübner), wireworms (Elateridae) and false wireworms (Te- nebrionidae), cutworms (Noctuida), southern dusty surface beetle (Tanymecus dilaticollis Gyllenhal), cotton bollworm (Helicoverpa armigera Hübner), and cereal aphids (Schizaphis graminum) Rondani. The database of the Hydrometeoro- logical Center of Ukraine was used to analyze climate parameters (2005–2021). The statistical analysis of the data was conducted using MS Excel and the linear correlation-regression analysis according to Pearson, Student’s criterion was used to evaluate the reliability (probability) of the correlation coefficients. Results. The results of correlational analysis of the state of populations of the main corn insect pests demonstrated that climate change has not considerably affected the number of corn borers as well as wireworms and false wireworms in all the natural and climatic zones of Ukraine yet. A reliable moderate reverse correlation (r = –0.309) was found between the number of cutworms and the sum of effective temperatures (SET) only for the Forest-Steppe conditions – under the increase in the SET, the number of these insects was smaller. The number of the southern dusty surface beetle was in direct, reliable, moderate correlation (r = 0.335) with the SET in the Steppe, for instance, the pest responded to the increase in the SET with the rise in its number. The number of cotton bollworms in Polissia was in reliable moderate correlation (r = –0.489) with the SET. The number of cereal aphids was in a reliable moderate direct correlation (r = 0.529) with the SET in Polissia: at the increase in the SET, the number of these pests was increasing. Conclusions. Conclusions: Climate changes do not considerably affect the state of the populations of the main corn insect pests in all the natural and climatic zones of Ukraine yet: we found the correlations between the number of insect pests and the SET which did not exceed such values as weak, moderate, and conspicuous. Significant changes in the state of insect pest populations should be expected if the sum of effective temperatures during the vegetation period will considerably affect the performance and feeding qualities of the cultivated plants.

Resistance and fitness costs of the Helicoverpa armigera after selection with the tetraniliprole newly developed diamide insecticide

The cotton bollworm (Helicoverpa armigera) (Lepidoptera: Noctuidae) is a highly destructive insect pest that feeds on more than 200 plants including cotton. Diamide insecticides are typically preferred to combat H. armigera. However, many reports of resistance to diamide insecticides such as chlorantraniliprole have been reported. Tetraniliprole is a novel diamide insecticide, but little is known about its resistance risk in H. armigera. After ten generations of treating H. armigera with tetraniliprole, neither the G4946 nor I4775 mutations were detected and no resistance to tetraniliprole was observed. The realized heritability (h2) was 0.094 after ten generations of selection with tetraniliprole, suggesting a low risk of resistance in H. armigera. Additionally, we found that the LD50 of tetraniliprole (4.01 μg/g) was lower than the LD50 of chlorantraniliprole (5.79 μg/g) in the susceptible strain. Molecular docking analysis also found a difference between the ryanodine receptor (RyR) binding sites of tetraniliprole and chlorantraniliprole, the tetraniliprole free binding energy to RyR was −6.9 kcal/mol, which was smaller than for chlorantraniliprole (−6.4 kcal/mol). Our study reveals that there is a low resistance risk to tetraniliprole in H. armigera, thus suggesting that tetraniliprole can be used as a substitute for other insecticides for this pest control.

Susceptibility of Bombyx mori larvae to the microsporidium Nosema bombycis from the silkworm and Nosema sp. from the cotton bollworm

Microsporidia are widespread parasites and cause diseases in economically important insects. A microsporidian isolate NspHA22 was discovered in the cotton bollworm Helicoverpa armigera in South-Western Russia. It showed 100 % sequence identity of small subunit rRNA gene to Nosema bombycis, a natural parasite of the silkworm Bombyx mori. However, after feeding second or third instar B. mori larvae with spores of the new isolate, insect mortality didn’t differ from that of the control, and no sporulation was revealed in alive and perished insects. In contrast, feeding N. bombycis spores isolated from B. mori resulted in high levels of host mortality and intense parasite sporulation at all the infection dose and larval instars used. This likely indicates that the isolate NspHA22 belongs to a species different from N. bombycis, in spite of identity of rDNA sequences.

Development of a soybean leaf disc assay for determining oral insecticidal activity in the lepidopteran agricultural pest Helicoverpa armigera

Pest insects pose a heavy burden on global agricultural industries with small molecule insecticides being predominantly used for their control. Unwanted side effects and resistance development plagues most small molecule insecticides such as the neonicotinoids, which have been reported to be harmful to honeybees. Bioinsecticides like Bacillus thuringiensis (Bt) toxins can be used as environmentally-friendly alternatives. Arachnid venoms comprise another promising source of bioinsecticides, containing a multitude of selective and potent insecticidal toxins. Unfortunately, no standardised insect models are currently available to assess the suitability of insecticidal agents under laboratory conditions. Thus, we aimed to develop a laboratory model that closely mimics field conditions by employing a leaf disk assay (LDA) for oral application of insecticidal agents in a bioassay tray format. Neonate larvae of the cotton bollworm (Helicoverpa armigera) were fed with soybean (Glycine max) leaves that were treated with different insecticidal agents. We observed dose-dependent insecticidal effects for Bt toxin and the neonicotinoid insecticide imidacloprid, with imidacloprid exhibiting a faster response. Furthermore, we identified several insecticidal arachnid venoms that were active when co-applied with sub-lethal doses of Bt toxin. We propose the H. armigera LDA as a suitable tool for assessing the insecticidal effects of insecticidal agents against lepidopterans.

Potential Biopesticides from Seed Extracts: A Sustainable Way to Protect Cotton Crops from Bollworm Damage

In the current study, the inhibitory effect of extracts from Gramineae (wheat, barley, and corn) and Leguminosae (sophora, bean, and pea) seeds was studied on the digestive alpha-amylase activity in cotton bollworm (Helicoverpa armigera Hubner). The insect was bred on artificial food based on Vigna unguiculata in the greenhouse condition (26 ± 2 °C, 60 ± 10% (Relative Humidity), R.H., 16:8 (Light: Darkness), L: D). The extracts of wheat (95.2%), barley (84.6%), corn (73.8%), sophora (77%), Vigna unguiculata (52%), and pea (56.7%) significantly inhibited the alpha-amylase activity in H. armigera. Studying the impact of different fractions (obtained via deposition at various concentrations of ammonium sulfate salt) on the alpha-amylase enzyme activity demonstrated that in 0–30% fractions, wheat, barley, and sophora have the highest effect (95.26%, 94.65%, and 94.73%, respectively) compared to the other fractions. The inhibitory activities of 0–30% fractions of corn, bean, and pea were 83.3, 56.94, and 50.92%, respectively. In 30–50% fractions, the most effective ones were those of wheat and barley with the inhibitory activity of 79.7% and 82.9%, respectively. In addition, bean and pea fractions inhibited 25.2% and 27.5%, in that order. No significant inhibitory impact was detected in 50–70% or higher fractions. The investigation of the impact of pH values (i.e., 2, 4, 8, and 10) on the inhibition of the alpha-amylase enzyme activity introduced 8–10 as the optimum pH in H. armigera. Nanotechnology offers several ways to enhance plant-based pesticides, which are a solution for making plant extract usage more efficient. The exploration of plant-based pesticides, in conjunction with the incorporation of nanotechnology and other scientific fields, offers a wide range of prospects for further investigation.

Insectivorous bats provide more pest suppression services than disservices - a case study in China

Many studies have investigated the role of insectivorous bats as natural enemies of agricultural pests. However, insectivorous bats have a broad diet, and whether their prey species are beneficial or harmful is unknown; thus, accurately assessing the services provided by bats is challenging. In China, most people, including farmers and plant protection workers, have an insufficient understanding of the ecological value of bats in biological control. Therefore, we collected the fecal samples of 10 bat species from three different sampling sites located in Guizhou Province, China, and conducted DNA metabarcoding to determine the diet composition of bats. We also categorized the prey species from the diet of bats as harmful or beneficial, based on previous studies, and recorded the industries they affect. Our results showed that the 10 bat species consumed prey from 19 orders and 96 families; most of them being lepidopterans. Among 564 total prey species recorded, 390 (69.15%) were pests and 28 (4.96%) were beneficial insects. Among them, 326 (57.80%) were agriculture or forestry pests, such as globally present Cotton bollworm (Helicoverpa armigera) and Beet armyworm (Spodoptera exigua). These results indicated that insectivorous bats have more beneficial effects than harmful effects, especially in the context of agriculture and forestry, as they suppressed very few beneficial arthropod mesopredators. By comparing the differences in the diet of I. io in different regions, we found that bats present in different regions can provide different predation services. Our study showed that insectivorous bats provide excellent pest suppression services in various industries and regions. It might be helpful for increasing awareness among people and bat conservation in China and other regions.

Suitability of Satellite Imagery for Surveillance of Maize Ear Damage by Cotton Bollworm (Helicoverpa armigera) Larvae

Suitability of Satellite Imagery for Surveillance of Maize Ear Damage by Cotton Bollworm (Helicoverpa armigera) Larvae

Endocytosis-mediated entry of a caterpillar effector into plants is countered by Jasmonate

Insects and pathogens release effectors into plant cells to weaken the host defense or immune response. While the imports of some bacterial and fungal effectors into plants have been previously characterized, the mechanisms of how caterpillar effectors enter plant cells remain a mystery. Using live cell imaging and real-time protein tracking, we show that HARP1, an effector from the oral secretions of cotton bollworm (Helicoverpa armigera), enters plant cells via protein-mediated endocytosis. The entry of HARP1 into a plant cell depends on its interaction with vesicle trafficking components including CTL1, PATL2, and TET8. The plant defense hormone jasmonate (JA) restricts HARP1 import by inhibiting endocytosis and HARP1 loading into endosomes. Combined with the previous report that HARP1 inhibits JA signaling output in host plants, it unveils that the effector and JA establish a defense and counter-defense loop reflecting the robust arms race between plants and insects.

Revision of Helicoverpa armigera insecticide resistance status in Greece

The cotton bollworm Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) is a major pest of numerous crops specially cotton and its control is mainly based on the application of insecticides. Studies on the efficacy levels of insecticides are limited in Greece and such information is essential of the implementation of rational IPM schemes. The aim of this study was to investigate the status of resistance against insecticides registered for the control of cotton bollworm, namely spinetoram, emamectin benzoate, lambda-cyhalothrin, cyantraniliprole and chlorantraniliprole on different populations. The insecticide resistance to the tested compounds was evaluated using laboratory dose-response bioassays in three field populations of H. armigera collected from cotton fields located in Larissa, Thessaloniki and Serres/Drama, Greece, during 2020 using artificial diets with chemical overlay. All tested populations of H. armigera remained susceptible to spinetoram (RR = 0.9–1), emamectin benzoate (RR = 1.2–2.4), cyantraniliprole (RR = 2.4–3.1) and chlorantraniliprole (RR = 1–1.9). While, lambda-cyhalothrin exhibited RR values between 4 and 46 folds in the tested populations, suggesting potential cases of resistance development. This study sets the foundation for evidence-based pest management in Greece and facilitates early detection of incipient resistance cases in the future.

Variation of Helicoverpa armigera symbionts across developmental stages and geographic locations.

Cotton bollworm (Helicoverpa armigera) poses a global problem, causing substantial economic and ecological losses. Endosymbionts in insects play crucial roles in multiple insect biological processes. However, the interactions between H. armigera and its symbionts have not been well characterized to date. We investigated the symbionts of H. armigera in the whole life cycle from different geographical locations. In the whole life cycle of H. armigera, Proteobacteria, Firmicutes, Bacteroidetes, and Actinobacteria were the dominant bacteria at the phylum level, while Enterococcus, Enterobacter, Glutamicibacter, and Bacillus were the four dominant bacteria at the genus level. Furthermore, high similarity in symbiotic bacterial community was observed in different stages of H. armigera, which were dominated by Enterococcus and Enterobacter. In fields, the dominant bacteria were Proteobacteria and Bacteroidetes, whereas, in the laboratory, the dominant bacteria were Proteobacteria. At the genus level, the dominant bacteria in cotton bollworm eggs of wild populations were Enterobacter, Morganella, Lactococcus, Asaia, Apibacter, and Enterococcus, and the subdominant bacteria were Bartonella, Pseudomonas, and Orbus. Moreover, the symbionts varied with geographical locations, and the closer the geographical distance, the more similar the microbial composition. Taken together, our study identifies and compares the symbiont variation along with geographical gradients and host development dynamic and reveals the high flexibility of microbiome communities in H. armigera, which probably benefits for the successful survival in a complicated changing environment.

Mechanisms of feeding cessation in Helicoverpa armigera larvae exposed to Bacillus thuringiensis Cry1Ac toxin

Insecticidal proteins from the bacterium Bacillus thuringiensis (Bt) have been applied in sprayable formulations and expressed in transgenic crops for the control of pests in the field. When exposed to Bt proteins insect larvae display feeding cessation, yet the mechanism for this phenomenon remains unknown. In this study, we investigated the feeding behavior and underlying mechanisms of cotton bollworm (Helicoverpa armigera) larvae after exposure to the Cry1Ac protein from Bt. Three H. armigera strains were studied: the susceptible SCD strain, the C2/3-KO strain with HaABCC2 and HaABCC3 knocked out and high-level resistance to Cry1Ac (>15,000-fold), and the SCD-KI strain with a T92C point mutation in tetraspanin (HaTSPAN1) and medium-level resistance to Cry1Ac (125-fold). When determining the percentage of insects that continued feeding after various exposure times to Cry1Ac, we observed quick cessation of feeding in larvae from the susceptible SCD strain, whereas larvae from the C2/3-KO strain did not display feeding cessation. In contrast, larvae from the SCD-KI strain rapidly recovered from the initial feeding cessation. Histopathological analyses and qRT-PCR in midguts of SCD larvae after Cry1Ac exposure detected serious epithelial damage and significantly reduced expression of the neuropeptide F gene (NPF) and its potential receptor gene NPFR, which are reported to promote insect feeding. Neither epithelial damage nor altered NPF and NPFR expression appeared in midguts of C2/3-KO larvae after Cry1Ac treatment. The same treatment in SCD-KI larvae resulted in milder epithelial damage and subsequent repair, and a decrease followed by an initial increase in NPF and NPFR expression. These results demonstrate that the feeding cessation response to Cry1Ac in cotton bollworm larvae is closely associated with midgut epithelial damage and downregulation of NPF and NPFR expression. This information provides clues to the mechanism of feeding cessation in response to Bt intoxication and contributes to the mode of action of the Cry1Ac toxin in target pests.

Absence of known knockdown resistance mutations but fixation of CYP337B3 was detected in field populations of Helicoverpa armigera across China

The cotton bollworm (Helicoverpa armigera) is a worldwide agricultural pest that infests many important crops. Pyrethroids targeting the voltage-gated sodium channel (VGSC) have been long used in the control of the cotton bollworm. Two amino acid substitutions (D1561V and E1565G) in H. armigera VGSC (HaVGSC) and the presence of a chimeric P450 gene (CYP337B3) have been documented to be associated with pyrethroid resistance. To understand the current occurrence of kdr mutations and the CYP337B3 gene in Chinese H. armigera populations, high-throughput amplicon sequencing was adopted to detect potential nucleotide variations in three fragments of the VGSC gene that cover 10 reported knockdown resistance (kdr) sites in insects, and gene-specific PCR was performed to examine the presence of CYP337B3 gene in H. armigera samples collected across China. The nucleotide variation analysis revealed a wealth of nucleotide variations in not only exons but also introns in the VGSC gene in Chinese H. armigera populations. However, neither previously reported kdr-conferring amino acid replacements nor other non-synonymous mutations were observed in a total of 1439 examined individuals. Population genetic analysis suggested that the H. armigera population in Nanchang, Jiangxi Province (JNC) had a moderate genetic differentiation from other populations, while no significant divergence was observed in other populations in northern and northwestern China. The CYP337B3 was present in all the examined individuals, indicating that CYP337B3 is extensively fixed in H. armigera populations across China. These results support that point mutations in VGSC are not a major factor involved in the current pyrethroid resistance in H. armigera. Instead, CYP337B3 plays a prevalent role in the development of resistance to pyrethroids in H. armigera.

Expressing Parasitoid Venom Protein VRF1 in an Entomopathogen Beauveria bassiana Enhances Virulence toward Cotton Bollworm Helicoverpa armigera.

Despite entomopathogenic fungi being used in various insect pest control, it is recognized that they could replace more chemical insecticides if they were more efficient. We have found that cotton bollworm Helicoverpa armigera responded to the infection of entomopathogenic fungus Beauveria bassiana by activating the Toll pathway. Koinobiont wasps also regulate host immunity and development to ensure the survival of their progeny. Previously, venom protein VRF1 was identified in Microplitis mediator. It enters H. armigera hemocytes, suppresses the expression of antimicrobial peptides (AMPs) by inhibiting the Toll pathway, and prevents parasite offspring from being encapsulated. With this in mind, we thought that it might be feasible to increase the virulence of B. bassiana by embedding VRF1 into its genome. Compared with that of wild-type (WT) B. bassiana, the median lethal dose (LD50) of the transformant expressing VRF1 (named BbVRF1) decreased approximately 2.36-fold, and the median time to lethality (LT50) was shortened to 84% when infecting H. armigera (a natural host of M. mediator). The AMP expression level of hemocytes in H. armigera infected with BbVRF1 strain was significantly downregulated compared to that in the control group infected with the WT. In addition, the LD50 of BbVRF1 against the fall armyworm Spodoptera frugiperda (an unnatural host of M. mediator) was decreased 3.45-fold and the LT50 was shortened to 73%, showing a greater virulence. Our research indicated that BbVRF1, an engineered strain of B. bassiana, has greater efficacy against pest insects both within and outside its host range (M. mediator), expanding the utilization of parasitoid wasp virulence effectors. IMPORTANCE Mycoinsecticides are essential for the development of integrated pest management as substitutes to chemical insecticides, but their usage is limited by their inferior virulence. Thus, genetically engineered bioinsecticides, including recombinant entomopathogenic fungi, have been regarded as a breakthrough to rapidly control pests. Deep knowledge of parasitoid wasps allows us to take advantage of this natural enemy of pest insects beyond raising them for field release. Our transformant BbVRF1 (Beauveria bassiana integrated with a venom protein VRF1 from Microplitis mediator) showed a higher virulence in H. armigera and S. frugiperda, demonstrating its potential for managing natural or unnatural hosts of M. mediator. This result provides a new strategy regarding which venom protein of parasitoid wasps can become part of the arsenal with which to equip entomopathogenic fungi. Utilizing parasitoid wasps with this approach could easily overcome the difficulties of artificial culture and enhance the virulence of other biocontrol agents.

20-hydroxyecdysone reprograms amino acid metabolism to support the metamorphic development of Helicoverpa armigera

Amino acid metabolism is regulated according to nutrient conditions; however, the mechanism is not fully understood. Using the holometabolous insect cotton bollworm (Helicoverpa armigera) as a model, we report that hemolymph metabolites are greatly changed from the feeding larvae to the wandering larvae and to pupae. Arginine, alpha-ketoglutarate (α-KG), and glutamate (Glu) are identified as marker metabolites of feeding larvae, wandering larvae, and pupae, respectively. Arginine level is decreased by 20-hydroxyecdysone (20E) regulation via repression of argininosuccinate synthetase (Ass) expression and upregulation of arginase (Arg) expression during metamorphosis. α-KG is transformed from Glu by glutamate dehydrogenase (GDH) inlarval midgut, which is repressed by 20E. The α-KG is then transformed to Glu by GDH-like in pupal fatbody, which is upregulated by 20E. Thus, 20E reprogrammed amino acid metabolism during metamorphosis by regulating gene expression in a stage- and tissue-specific manner to support insect metamorphic development.

An entomopathogenic fungus exploits its host humoral antibacterial immunity to minimize bacterial competition in the hemolymph

BackgroundThe insect hemolymph (blood-equivalent fluid), composed of a large number of hemocytes (blood cells) and a variety of soluble immune effectors, is hostile for pathogens including fungi. In order to survive in the insect hemocoel (body cavity), the entomopathogenic fungus (EPF) has evolved two classical coping strategies, namely evasion and suppression of the host immune reactions. However, it remains unclear whether EPF has other ways of coping with host immunity.ResultsIn this study, we demonstrated that Metarhizium rileyi (an EPF) infection by injection of blastospores into the hemocoel enhanced the plasma antibacterial activity of cotton bollworm (Helicoverpa armigera), which was partially due to the enhanced expression of antimicrobial peptides (AMPs). The early stage of M. rileyi infection induced the translocation of gut bacteria into the hemocoel, where they were subsequently cleared due to the enhanced plasma antibacterial activity. Further, we showed that the enhanced plasma antibacterial activity and AMP expression were attributable to M. rileyi but not the invasive gut bacteria (opportunistic bacteria). Elevated ecdysone (major steroid hormone in insects) levels in the hemolymph at 48 h post-M. rileyi infection might contribute to the enhanced expression of AMPs. The fungus-elicited AMPs, such as cecropin 3 or lebocin, exhibited potent inhibitory activity against the opportunistic bacteria but not against hyphal bodies. In addition, the opportunistic bacteria competed with hyphal bodies for amino acid nutrients.ConclusionsM. rileyi infection induced the translocation of gut bacteria, and then the fungi activated and exploited its host humoral antibacterial immunity to eliminate opportunistic bacteria, preventing them from competing for nutrients in the hemolymph. Unlike the classical strategies, EPF utilizes to evade or suppress host immunity, our findings reveal a novel strategy of interaction between EPF and host immunity.BbkogtQagejkWT1MfyqrGJVideo

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.