A brave new world for an old world pest: Helicoverpa armigera (Lepidoptera: Noctuidae) in Brazil

Development of resistance monitoring for Helicoverpa armigera (Lepidoptera: Noctuidae) resistance to pyramided Bt cotton in China

The cotton bollworm, Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae), is a significant cotton pest worldwide. Bacillus thuringiensis (Bt) cotton producing Cry1Ac has been used since 1997 for the control of this pest in China and a significant increase in H. armigera resistance to Cry1Ac has occurred in northern China. To mitigate resistance evolution, it is necessary to develop and plant pyramided 2- and 3-toxin Bt cotton to replace Cry1Ac cotton. For sustainable use of pyramided Bt cotton, we used diet overlay bioassays to measure the baseline susceptibility of H. armigera to Cry2Ab in 33 populations collected in 2017, 2018, and 2021 in 12 locations from major cotton-producing areas of China. The lethal concentration killing 50% (LC50) or 99% (LC99) of individuals from the populations ranged from 0.030 to 0.138 µg/cm2 and 0.365 to 2.964 µg/cm2, respectively. The ratio of the LC50 for the most resistant and susceptible population was 4.6, indicating moderate among-population variability in resistance. The susceptibility of H. armigera to Cry2Ab did not vary significantly over years. A diagnostic concentration of 2 µg/cm2 was calculated as twice the LC99 from an analysis of pooled data for the field-collected populations. This concentration discriminated well between susceptible and resistant individuals, as it killed all larvae from a susceptible laboratory strain and 0%, 0%, and 23% of larvae from 3 laboratory strains with > 100-fold resistance to Cry2Ab. These baseline susceptibility data and diagnostic concentration for Cry2Ab will be useful for monitoring the evolution of H. armigera resistance to pyramided Bt cotton in China.

An Improved Bulk DNA Extraction Method for Detection of Helicoverpa armigera (Lepidoptera: Noctuidae) Using Real-Time PCR

Helicoverpa armigera is among the most problematic agricultural pests worldwide due to its polyphagy and ability to evolve pesticide resistance. Molecular detection methods for H. armigera have been developed to track its spread, as such methods allow for rapid and accurate differentiation from the native sibling species H. zea. Droplet digital PCR (ddPCR) is a preferred method for bulk screening due to its accuracy and tolerance to PCR inhibitors; however, real-time PCR is less expensive and more widely available in molecular labs. Improvements to DNA extraction yield, purity, and throughput are crucial for real-time PCR assay optimization. Bulk DNA extractions have recently been improved to where real-time PCR sensitivity can equal that of ddPCR, but these new methods require significant time and specialized equipment. In this study, we improve upon previously published bulk DNA extraction methods by reducing bench time and materials. Our results indicate that the addition of caffeine and RNase A improves DNA extraction, resulting in lower Cq values during real-time PCR while reducing the processing time and cost per specimen. Such improvements will enable the use of high throughput screening methods across multiple platforms to improve the probability of detection of H. armigera.

Rapid Adaptation and Interspecific Introgression in the North American Crop Pest Helicoverpa zea

Insect crop pests threaten global food security. This threat is amplified through the spread of nonnative species and through adaptation of native pests to control measures. Adaptations such as pesticide resistance can result from selection on variation within a population, or through gene flow from another population. We investigate these processes in an economically important noctuid crop pest, Helicoverpa zea, which has evolved resistance to a wide range of pesticides. Its sister species Helicoverpa armigera, first detected as an invasive species in Brazil in 2013, introduced the pyrethroid-resistance gene CYP337B3 to South American H. zea via adaptive introgression. To understand whether this could contribute to pesticide resistance in North America, we sequenced 237 H. zea genomes across 10 sample sites. We report H. armigera introgression into the North American H. zea population. Two individuals sampled in Texas in 2019 carry H. armigera haplotypes in a 4 Mbp region containing CYP337B3. Next, we identify signatures of selection in the panmictic population of nonadmixed H. zea, identifying a selective sweep at a second cytochrome P450 gene: CYP333B3. We estimate that its derived allele conferred a ∼5% fitness advantage and show that this estimate explains independently observed rare nonsynonymous CYP333B3 mutations approaching fixation over a ∼20-year period. We also detect putative signatures of selection at a kinesin gene associated with Bt resistance. Overall, we document two mechanisms of rapid adaptation: the introduction of fitness-enhancing alleles through interspecific introgression, and selection on intraspecific variation.

Ascertaining variations in the activity of larval midgut enzymes of Helicoverpa armigera by dietary emamectin benzoate through biochemical and in silico docking study

Helicoverpa armigera, a ubiquitous polyphagous pest, poses a significant threat to global agriculture, causing substantial economic losses and demonstrating resistance to synthetic pesticides. This study investigates the potential of emamectin benzoate (EMB), an avermectin derivative, as an effective control agent against H. armigera. The larvae of the NBII-MP-NOC-01 strain of H. armigera were reared on an artificial diet. The impact of dietary EMB was examined on four midgut enzymes; alanine aminotransferase (ALT), aspartate aminotransferase (AST), acid phosphatase (ACP), and alkaline phosphatase (ALP). Results showed a dose-dependent and time-dependent reduction in ALT and AST activity, while an initial increase and subsequent decline in ACP and ALP activity at higher EMB concentrations. Computational modelling of enzyme structures and molecular docking studies revealed differential binding of EMB with the midgut enzymes. The strongest interaction was observed between EMB and ALT residues, contrasting with weakest interactions observed with AST. The study also showed that decreased activity of transaminases in H. armigera caused by EMB may be because of stability-activity trade-off, while in phosphatases reverse may be the case. This research provides crucial insights into the biochemical responses and the intricate insecticide-enzyme interactions in H. armigera caused by EMB exposure. This study lays the foundation for further research aimed at developing environmentally friendly approaches for managing H. armigera, addressing the challenges associated with conventional pesticides.

Cyclotides: The next generation in biopesticide development for eco-friendly agriculture

Chemical pesticides remain the predominant method for pest management in numerous countries. Given the current landscape of agriculture, the development of biopesticides has become increasingly crucial. The strategy empowers farmers to efficiently manage pests and diseases, while prioritizing minimal adverse effects on the environment and human health, hence fostering sustainable management. In recent years, there has been a growing interest and optimism surrounding the utilization of peptide biopesticides for crop protection. These sustainable and environmentally friendly substances have been recognized as viable alternatives to synthetic pesticides due to their outstanding environmental compatibility and efficacy. Numerous studies have been conducted to synthesize and identify peptides that exhibit activity against significant plant pathogens. One of the peptide classes is cyclotides, which are cyclic cysteine-rich peptides renowned for their wide range of sequences and functions. In this review, we conducted a comprehensive analysis of cyclotides, focusing on their structural attributes, developmental history, significant biological functions in crop protection, techniques for identification and investigation, and the application of biotechnology to enhance cyclotide synthesis. The objective is to emphasize the considerable potential of cyclotides as the next generation of plant protection agents on the global scale.

Hybrids of two destructive subterranean termites established in the field, revealing a potential for gene flow between species

Hybridization between invasive pest species may lead to significant genetic and economic impacts that require close monitoring. The two most invasive and destructive termite species worldwide, Coptotermes formosanus Shiraki and Coptotermes gestroi (Wasmann), have the potential for hybridization in the field. A three-year field survey conducted during the dispersal flight season of Coptotermes in Taiwan identified alates with atypical morphology, which were confirmed as hybrids of the two Coptotermes species using microsatellite and mitochondrial analyses. Out of 27,601 alates collected over three years, 4.4% were confirmed as hybrid alates, and some advanced hybrids (>F1 generations) were identified. The hybrid alates had a dispersal flight season that overlapped with the two parental species 13 out of 15 times. Most of the hybrid alates were females, implying that mating opportunities beyond F1 may primarily be possible through female hybrids. However, the incipient colony growth results from all potential mating combinations suggest that only backcross colonies with hybrid males could sometimes lead to brood development. The observed asymmetrical viability and fertility of hybrid alates may critically reduce the probability of advanced-hybrid colonies being established in the field.

Improved effects of Helicoverpa armigera nucleopolyhedrovirus integrated with Campoletis chlorideae against H. armigera and impact of the virus on the parasitoid

BACKGROUND

Combined use can be an effective measure to improve pest control by viruses and parasitic wasps. However, not all combinations of natural enemies show improved effects. Helicoverpa armigera nucleopolyhedrovirus (HearNPV) and Campoletis chlorideae Uchida are two important natural enemies of Helicoverpa armigera. This study aimed to investigate the combined effects of C. chlorideae and HearNPV against H. armigera larvae and the impact of HearNPV on C. chlorideae.

RESULTS

The combination of HearNPV and C. chlorideae exerted increased mortality on H. armigera when C. chlorideae parasitized larvae one day after infection with HearNPV. C. chlorideae could distinguish between HearNPV-infected and noninfected larvae. Besides influencing host selection of C. chlorideae, HearNPV infection had negative effects on the development and reproduction of C. chlorideae. The developmental time of C. chlorideae was significantly prolonged and the percentage of emergence and adult eclosion of C. chlorideae was lower in infected hosts. The adult wasps were also smaller in body size, and female adults had fewer eggs when they developed in virus-infected hosts.

CONCLUSIONS

HearNPV combined with C. chlorideae could improve the efficacy of biological control against H. armigera. The results provided valuable information on the importance of timing in the combined use of HearNPV and C. chlorideae for the biological control of H. armigera. © 2023 Society of Chemical Industry.

Beauveria bassiana biogenic nanoparticles for the control of Noctuidae pests

BACKGROUND

Biogenic metallic and oxide metal nanoparticles have potential as alternatives for several current problems in agriculture, such as the control of caterpillars which cause huge losses in the production of important crops. In the present study, capped and uncapped silver, iron oxide and titanium dioxide nanoparticles were synthesized from the filtrate of Beauveria bassiana and evaluated in regard to physico-chemical characteristics, capping composition, cytotoxicity, genotoxicity and biological activity on Helicoverpa armigera and Spodoptera frugiperda caterpillars.

RESULTS

A difference in the physico-chemical parameters of the capped and uncapped nanoparticles was observed, with larger aggregation and lower stability of the uncapped. In regard to the study of the capping, the presence of functional groups of biomolecules as well as the activity of B. bassiana hydrolytic enzymes were observed. Cytotoxic effects on the tested cell lines were not observed and DNA damage levels increased with more intense effects of the uncapped nanoparticles. In regard to the biological activity against Noctuidae pests, the uncapped and capped iron oxide, and uncapped titanium dioxide nanoparticles occasioned higher mortality (76%, 60% and 51%, respectively) but no differences in LC50 were recorded. Moreover, sublethal effects were reported on Helicoverpa armigera whereas Spodoptera frugiperda showed low susceptibility to the nanoparticles.

CONCLUSION

The results demonstrate that biogenic metallic and oxide metal nanoparticles might show promising effects for the control of caterpillars which cause damage on important agricultural crops. Further investigations are necessary to understand the mechanisms of action and optimize the biological activity of these new nanomaterials. © 2023 Society of Chemical Industry.

Heterologous expression, biochemical characterization and prospects for insecticide biosensing potential of carboxylesterase Ha006a from Helicoverpa armigera

Enzymes have attracted considerable scientific attention for their crucial role in detoxifying a wide range of harmful compounds. In today's global context, the extensive use of insecticides has emerged as a significant threat to the environment, sparking substantial concern. Insects, including economically important pests like Helicoverpa armigera, have developed resistance to conventional pest control methods through enzymes like carboxyl/cholinesterases. This study specifically focuses on a notable carboxyl/cholinesterase enzyme from Helicoverpa armigera (Ha006a), with the goal of harnessing its potential to combat environmental toxins. A total of six insecticides belonging to two different classes displayed varying inhibitory responses towards Ha006a, thereby rendering it effective in detoxifying a broader spectrum of insecticides. The significance of this research lies in discovering the bioremediation property of Ha006a, as it hydrolyzes synthetic pyrethroids (fenvalerate, λ-cyhalothrin and deltamethrin) and sequesters organophosphate (paraoxon ethyl, profenofos, and chlorpyrifos) insecticides. Additionally, the interaction studies between organophosphate insecticides and Ha006a helped in the fabrication of a novel electroanalytical sensor using a modified carbon paste electrode (MCPE). This sensor boasts impressive sensitivity, with detection limits of 0.019 μM, 0.15 μM, and 0.025 μM for paraoxon ethyl, profenofos, and chlorpyrifos, respectively. This study provides a comprehensive biochemical and biophysical characterization of the purified esterase Ha006a, showcasing its potential to remediate different classes of insecticides.

Ontogenetic Changes in the Feeding Behaviour of Helicoverpa armigera Larvae on Pigeonpea (Cajanus cajan) Flowers and Pods

Despite substantial research examining caterpillar-plant interactions, changes in the feeding behaviour of lepidopteran larvae as they develop are poorly understood. In this study, we investigated ontogenetic changes in the behaviour of Helicoverpa armigera larvae feeding on reproductive structures of pigeonpea (Cajanus cajan). Specifically, we examined the preference for and avoidance of pigeonpea flowers and pods of first, second, third, and fourth instar H. armigera larvae. We also conducted a no-choice assay to compare the ability of third and fourth instar larvae to penetrate pigeonpea pod walls, which act as a physical defence against herbivory. When presented with a choice between pigeonpea pods and flowers, different instars behaved differently. First and second instar larvae largely avoided pigeonpea pods, instead feeding on flowers; third instar larvae initially avoided pods, but by 24 h, did not strongly discriminate between the structures; and fourth instars demonstrated a preference for pods. When initially placed on pods, first instars were slower than other instars to leave these structures, despite pods being suboptimal feeding sites for small caterpillars. We identified a clear instar-specific ability to penetrate through the pod wall to reach the seeds. Most third instar larvae were unable to penetrate the pod wall, whereas most fourth instars succeeded. Third instars suffered a physiological cost (measured by relative growth rate) when boring through the pod wall, which was not observed in fourth instars. Our study further illuminates the insect-plant interactions of the H. armigera-pigeonpea system and provides evidence for the significant changes in feeding behaviour that may occur during lepidopteran larval development.

The effect of missing data on evolutionary analysis of sequence capture bycatch, with application to an agricultural pest

Sequence capture is a genomic technique that selectively enriches target sequences before high throughput next-generation sequencing, to generate specific sequences of interest. Off-target or 'bycatch' data are often discarded from capture experiments, but can be leveraged to address evolutionary questions under some circumstances. Here, we investigated the effects of missing data on a variety of evolutionary analyses using bycatch from an exon capture experiment on the global pest moth, Helicoverpa armigera. We added > 200 new samples from across Australia in the form of mitogenomes obtained as bycatch from targeted sequence capture, and combined these into an additional larger dataset to total > 1000 mitochondrial cytochrome c oxidase subunit I (COI) sequences across the species' global distribution. Using discriminant analysis of principal components and Bayesian coalescent analyses, we showed that mitogenomes assembled from bycatch with up to 75% missing data were able to return evolutionary inferences consistent with higher coverage datasets and the broader literature surrounding H. armigera. For example, low-coverage sequences broadly supported the delineation of two H. armigera subspecies and also provided new insights into the potential for geographic turnover among these subspecies. However, we also identified key effects of dataset coverage and composition on our results. Thus, low-coverage bycatch data can offer valuable information for population genetic and phylodynamic analyses, but caution is required to ensure the reduced information does not introduce confounding factors, such as sampling biases, that drive inference. We encourage more researchers to consider maximizing the potential of the targeted sequence approach by examining evolutionary questions with their off-target bycatch where possible-especially in cases where no previous mitochondrial data exists-but recommend stratifying data at different genome coverage thresholds to separate sampling effects from genuine genomic signals, and to understand their implications for evolutionary research.

Cas9-Mediated Gene Editing Using Receptor-Mediated Ovary Transduction of Cargo (ReMOT) Control in Bombyx mori

Lepidoptera is one of the most speciose insect orders, causing enormous damage to agricultural and forest crops. Although genome editing has been achieved in a few Lepidoptera for insect controls, most techniques are still limited. Here, by injecting female pupae of the Lepidoptera model species, Bombyx mori, gene editing was established using the Receptor-Mediated Ovary Transduction of Cargo (ReMOT) control technique. We identified a B. mori oocytes-targeting peptide ligand (BmOTP, a 29 aa of vitellogenin N-terminal of silkworms) with a highly conserved sequence in lepidopteran insects that could efficiently deliver mCherry into oocytes. When BmOTP was fused to CRISPR-associated protein 9 (Cas9) and the BmOTP-Cas9 ribonucleoprotein complex was injected into female pupae, heritable editing of the offspring was achieved in the silkworms. Compared with embryo microinjection, individual injection is more convenient and eliminates the challenge of injecting extremely small embryos. Our results will significantly facilitate the genetic manipulation of other lepidopteran insects, which is essential for advancing lepidopteran pest control.

Norsesquiterpenes from the Latex of Euphorbia dentata and Their Chemical Defense Mechanisms against Helicoverpa armigera

Euphorbia dentata (Euphorbiaceae), an invasive weed, is rarely eaten by herbivorous insects and could secrete a large amount of white latex, causing a serious threat to local natural vegetation, agricultural production and human health. In order to prevent this plant from causing more negative effects on humans, it is necessary to understand and utilize the chemical relationships between the latex of E. dentata and herbivorous insects. In this study, three new norsesquiterpenes (1-3), together with seven known analogues (4-10), were isolated and identified from the latex of E. dentata. All norsesquiterpenes (1-10) showed antifeedant and growth-inhibitory effects on H. armigera with varying levels, especially compounds 1 and 2. In addition, the action mechanisms of active compounds (1-3) were revealed by detoxifying enzyme (AchE, CarE, GST and MFO) activities and corresponding molecular docking analyses. Our findings provide a new idea for the development and utilization of the latex of E. dentata, as well as a potential application of norsesquiterpenes in botanical insecticides.

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.

Genome Mining and Molecular Networking Guided Isolation of Antimycin Analogs with Antifeedant Activities from the Deep-Sea-Derived Streptomyces sp. NA13

Polyphagous insects could affect agricultural production, which leads to serious economic losses. Due to the negative effects of synthesized insecticides, finding eco-friendly and new biopesticides is emergent. To develop natural origin insecticides, an integrative approach combining antifeedant activity screening, genome mining, and molecular networking has been applied to discover antifeedant secondary metabolites from Streptomyces sp. NA13, which leads to the isolation of a novel antimycin Q (1) and six known antimycin analogs (antimycins A1a, A2a, A3a, A4a, A7a, and N-formylantimycic acid methyl ester, 2-7). Their structures were identified by high-resolution mass spectrometry (HR-MS) and nuclear magnetic resonance (NMR) spectroscopic. The absolute configuration of 1 was elucidated by the comparison of coupling constant, electronic circular dichroism (ECD) analysis, and NMR calculations. 1-6 exhibited different levels of antifeedant activities against Helicoverpa armigera, especially 1-4. At the same time, the antifeedant activity of antimycin was reported firstly.

A Comparative Study of Transcriptional Regulation Mechanism of Cytochrome P450 CYP6B7 between Resistant and Susceptible Strains of Helicoverpa armigera

Cytochrome P450 CYP6B7 has previously been proved to be associated with fenvalerate-resistance in Helicoverpa armigera. Here, how CYP6B7 is regulated and involved in the resistance of H. armigera is studied. Seven base differences (M1-M7) were found in CYP6B7 promoter between a fenvalerate-resistant (HDTJFR) and a susceptible (HDTJ) strain of H. armigera. M1-M7 sites in HDTJFR were mutated into the corresponding base in HDTJ, and pGL3-CYP6B7 reporter genes with different mutation sites were constructed. Fenvalerate-induced activities of reporter genes mutated at M3, M4, and M7 sites were significantly reduced. Transcription factors Ubx and Br, whose binding sites contain M3 and M7, respectively, were overexpressed in HDTJFR. Knockdown of Ubx and Br results in significant expression inhibition of CYP6B7 and other resistance-related P450 genes, and increase of sensitivity of H. armigera to fenvalerate. These results indicate that Ubx and Br regulate the expression of CYP6B7 to mediate the fenvalerate-resistance in H. armigera.

Farnesol dehydrogenase from Helicoverpa armigera (Hübner) as a promising target for pest management: molecular docking, in vitro and insect bioassay studies using geranylgeraniol as potential inhibitor

Juvenile hormone (JH) plays pivotal roles in several critical developmental processes in insects, including metamorphosis and reproduction. JH-biosynthetic pathway enzymes are considered highly promising targets for discovering novel insecticides. The oxidation of farnesol to farnesal, catalysed by farnesol dehydrogenase (FDL), represents a rate-limiting step in JH biosynthesis. Here, we report farnesol dehydrogenase (HaFDL) from H. armigera as a promising insecticidal target. The inhibitory potential of natural substrate analogue geranylgeraniol (GGol) was tested in vitro, wherein it showed a high binding affinity (kd 595 µM) for HaFDL in isothermal titration calorimetry (ITC) and subsequently exhibited dose-dependent enzyme inhibition in GC-MS coupled qualitative enzyme inhibition assay. Moreover, the experimentally determined inhibitory activity of GGol was augmented by the in silico molecular docking simulation which showed that GGol formed a stable complex with HaFDL, occupied the active site pocket and interacted with key active site residues (Ser147 and Tyr162) as well as other residues that are crucial in determining the active site architecture. Further, the diet-incorporated oral feeding of GGol caused detrimental effects on larval growth and development, exhibiting a significantly reduced rate of larval weight gain (P < 0.01), aberrant pupal and adult morphogenesis, and a cumulative mortality of ~ 63%. To the best of our knowledge, the study presents the first report on evaluating GGol as a potential inhibitor for HaFDL. Overall, the findings revealed the suitability of HaFDL as a potential insecticidal target for the management H. armigera.

Advances in omics research on peanut response to biotic stresses

Peanut growth, development, and eventual production are constrained by biotic and abiotic stresses resulting in serious economic losses. To understand the response and tolerance mechanism of peanut to biotic and abiotic stresses, high-throughput Omics approaches have been applied in peanut research. Integrated Omics approaches are essential for elucidating the temporal and spatial changes that occur in peanut facing different stresses. The integration of functional genomics with other Omics highlights the relationships between peanut genomes and phenotypes under specific stress conditions. In this review, we focus on research on peanut biotic stresses. Here we review the primary types of biotic stresses that threaten sustainable peanut production, the multi-Omics technologies for peanut research and breeding, and the recent advances in various peanut Omics under biotic stresses, including genomics, transcriptomics, proteomics, metabolomics, miRNAomics, epigenomics and phenomics, for identification of biotic stress-related genes, proteins, metabolites and their networks as well as the development of potential traits. We also discuss the challenges, opportunities, and future directions for peanut Omics under biotic stresses, aiming sustainable food production. The Omics knowledge is instrumental for improving peanut tolerance to cope with various biotic stresses and for meeting the food demands of the exponentially growing global population.

Discovery of novel (N-aryl-4-methylpiperidinyl)pyrazoles: a new class of potent lepidopteran insecticides

BACKGROUND

Insects of the order Lepidoptera are among the most destructive global pests, causing billions of dollars in damage annually. A new class of N-arylpyrazole-4-methylpiperidines with potent activity on lepidopteran species has been discovered.

RESULTS

In a high-throughput insecticide screen compound 1 was identified to possess modest activity on the lepidopteran insect Plutella xylostella. Optimization of 1 to compound 42 resulted in a compound with excellent activity on Spodoptera exigua, Spodoptera frugiperda, and Helicoverpa zea with median lethal concentrations values of 2.8, 1.4, and 12.5 ppm respectively. Although the mode of action remains unknown, these compounds do not appear to work by many of the known biochemical mechanisms of insect control.

CONCLUSION

N-Arylpyrazole-4-methylpiperidines represent a new class of insecticides with excellent activity on a broad spectrum of lepidopteran pests. Studies to date indicate the potential for a novel mode of action; however, the target site is unknown at present. © 2023 Society of Chemical Industry.

The plant specialized metabolite epicatechin- 3-gallate (EC3G) perturbs lipid metabolism and attenuates fat accumulation in pigeonpea pod borer, Helicoverpa armigera

Control of pod borer Helicoverpa armigera, a notorious polyphagous pest requires paramount attention with focus on environment-friendly management approaches. Overproduction of catechins (epigallocatechin-EGC and epicatechin-3-gallate-EC3G) in the pod borer-resistant pigeonpea wild relative, Cajanus platycarpus during continued herbivory prodded us to assess their underlying molecular effect on H. armigera. Significant reduction in larval and pupal growth parameters was observed when reared on artificial diet incorporated with 100 ppm EC3G vis a vis 100 ppm EGC and EGC + EC3G. Comparative RNAseq analyses of larvae that fed on normal and EC3G-incorporated diet revealed 62 differentially expressed genes dominated by detoxification and lipid metabolism. While lipase and fatty acid-binding protein 2-like were up-regulated, delta9-FADS-like involved in fatty acid synthesis was downregulated, indicating effect of EC3G on fat metabolism. Validation of RNAseq data by qPCR; midgut glutathione-S-transferase and esterase assays depicted increased lipolysis and reduced lipogenesis in EC3G-fed larvae. Additionally, differential accumulation of stearic acid and oleic acid in EC3G-fed and control larvae/adults ascertained perturbation in lipogenesis. Supported by modelling, molecular docking and simulations, we demonstrate the possible involvement of the insect adipokinetic hormone receptor (AKHR) in the EC3G-mediated response. The study demonstrates plant specialized metabolite EC3G as a potential candidate for H. armigera control.

A Chromosome-Scale Genome Assembly of a Helicoverpa zea Strain Resistant to Bacillus thuringiensis Cry1Ac Insecticidal Protein

Helicoverpa zea (Lepidoptera: Noctuidae) is an insect pest of major cultivated crops in North and South America. The species has adapted to different host plants and developed resistance to several insecticidal agents, including Bacillus thuringiensis (Bt) insecticidal proteins in transgenic cotton and maize. Helicoverpa zea populations persist year-round in tropical and subtropical regions, but seasonal migrations into temperate zones increase the geographic range of associated crop damage. To better understand the genetic basis of these physiological and ecological characteristics, we generated a high-quality chromosome-level assembly for a single H. zea male from Bt-resistant strain, HzStark_Cry1AcR. Hi-C data were used to scaffold an initial 375.2 Mb contig assembly into 30 autosomes and the Z sex chromosome (scaffold N50 = 12.8 Mb and L50 = 14). The scaffolded assembly was error-corrected with a novel pipeline, polishCLR. The mitochondrial genome was assembled through an improved pipeline and annotated. Assessment of this genome assembly indicated 98.8% of the Lepidopteran Benchmark Universal Single-Copy Ortholog set were complete (98.5% as complete single copy). Repetitive elements comprised approximately 29.5% of the assembly with the plurality (11.2%) classified as retroelements. This chromosome-scale reference assembly for H. zea, ilHelZeax1.1, will facilitate future research to evaluate and enhance sustainable crop production practices.

In silico identification of potential phytochemical inhibitors targeting farnesyl diphosphate synthase of cotton bollworm (Helicoverpa armigera)

Helicoverpa armigera (Ha), a polyphagous pest, causes significant damage to several crop plants, including cotton. The control of this cosmopolitan pest is largely challenging due to the development of resistance to existing management practices. The Juvenile Hormone (JH) plays a pivotal role in the life cycle of insects by regulating their morphogenetic and gonadotropic development. Hence, enzymes involved in JH biosynthesis are an attractive target for the development of selective insecticides. Farnesyl diphosphate synthase (FPPS), a member protein of (E)-prenyl-transferases, is one of the most crucial enzymes in the biosynthetic pathway of JHs. It catalyzes the condensation of isopentenyl diphosphate (IPP) with dimethylallyl diphosphate (DMAPP), forming farnesyl diphosphate (FPP), a precursor of JH. The study was designed to identify an effective small inhibitory molecule that could inhibit the activity of Helicoverpa armigera - FPPS (HaFPPS) for an effective pest control intervention. Therefore, a 3D model of FPPS protein was generated using homology modeling. The FooDB database library of small molecules was selected for virtual screening, following which binding affinities were evaluated using docking studies. Three top-scored molecules were analyzed for various pharmacophore properties. Further, molecular dynamics (MD) simulation analysis showed that the identified molecules (mitraphylline-ZINC1607834, chlorogenic acid-ZINC2138728 and llagate-ZINC3872446) had a reasonably acceptable binding affinity for HaFPPS and resulted in the formation of a stable HaFPPS-inhibitor(s) complex. The identified phytochemical molecules may be used as potent inhibitors of HaFPPS thus, paving the way for further developing environment-friendly insect growth regulator(s). Communicated by Ramaswamy H. Sarma.

Helicoverpa armigera preference and performance on three cultivars of short-duration pigeonpea (Cajanus cajan): the importance of whole plant assays

BACKGROUND

Helicoverpa armigera is a major pest of pigeonpea (Cajanus cajan). Efforts to develop pigeonpea varieties resistant to H. armigera attack have been met with limited success, despite reports of high levels of resistance to H. armigera in wild relatives of pigeonpea and reports of low to moderate levels of resistance in cultivated varieties. Here we examined H. armigera oviposition preference and larval performance on whole plants of three cultivars of short-duration pigeonpea: a susceptible control (ICPL 87) and two cultivars with purported host-plant resistance (ICPL 86012 and ICPL 88039).

RESULTS

In our no-choice oviposition experiment, H. armigera laid similar numbers of eggs on all three cultivars tested, but under choice conditions moths laid slightly more eggs on ICPL 88039. Larval growth and development were affected by cultivar, and larvae grew to the largest size (weight) and developed fastest on ICPL 86012. Moths laid most of their eggs on floral structures, sites where subsequent early instar larvae overwhelmingly fed. Experimentally placing neonate larvae at different locations on plants demonstrated that larvae placed on flowers experienced greater survival, faster development, and greater weight gain than those placed on leaves. The type and density of trichomes (a potential resistance trait) differed among cultivars and plant structures, but larvae selected to feed at sites where trichomes were absent.

CONCLUSION

Future work examining host-plant resistance against H. armigera should incorporate the behavioural preference of moths and larvae in experiments using whole plants as opposed to bioassays of excised plant parts in Petri dishes. © 2022 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Complex multiple introductions drive fall armyworm invasions into Asia and Australia

The fall armyworm (FAW) Spodoptera frugiperda is thought to have undergone a rapid 'west-to-east' spread since 2016 when it was first identified in western Africa. Between 2018 and 2020, it was recorded from South Asia (SA), Southeast Asia (SEA), East Asia (EA), and Pacific/Australia (PA). Population genomic analyses enabled the understanding of pathways, population sources, and gene flow in this notorious agricultural pest species. Using neutral single nucleotide polymorphic (SNP) DNA markers, we detected genome introgression that suggested most populations in this study were overwhelmingly C- and R-strain hybrids (n = 252/262). SNP and mitochondrial DNA markers identified multiple introductions that were most parsimoniously explained by anthropogenic-assisted spread, i.e., associated with international trade of live/fresh plants and plant products, and involved 'bridgehead populations' in countries to enable successful pest establishment in neighbouring countries. Distinct population genomic signatures between Myanmar and China do not support the 'African origin spread' nor the 'Myanmar source population to China' hypotheses. Significant genetic differentiation between populations from different Australian states supported multiple pathways involving distinct SEA populations. Our study identified Asia as a biosecurity hotspot and a FAW genetic melting pot, and demonstrated the use of genome analysis to disentangle preventable human-assisted pest introductions from unpreventable natural pest spread.

In Silico and In Vivo Evaluation of Synthesized SCP-2 Inhibiting Compounds on Life Table Parameters of Helicoverpa armigera (Hübner)

For environment-friendly, safe and nonpersistent chemical control of a significant polyphagous insect pest, Helicoverpa armigera, discovery of growth-regulating xenobiotics can offer a sustainable alternative to conventional insecticides. For this purpose, chemically synthesized compounds to inhibit sterol carrier protein (SCP-2) function using in silico and in vivo assays were evaluated to estimate their impact on the survivals and lifetable indices of H. armigera. From nine chemically synthesized compounds, OA-02, OA-06 and OA-09 were selected for this study based on binding poses mimicking cholesterol, a natural substrate of sterol carrier protein and molecular dynamics simulations. In vivo bioassays revealed that all compounds significantly reduced the larval and pupal weight accumulations and stadia lengths. Subsequently, the pupal periods were prolonged upon treatment with higher doses of the selected compounds. Moreover, OA-09 significantly reduced pupation and adult emergence rates as well as the fertility of female moths; however, fecundity remained unaffected, in general. The life table parameters of H. armigera were significantly reduced when treated with OA-09 at higher doses. The population treated with 450 μM of OA-09 had the least net reproductive rates (Ro) and gross reproductive rate (GRR) compared to the control population. The same compound resulted in a declining survival during the early stages of development coupled with reduced larval and pupal durations, and fertility. These results have a significant implication for developing an effective and sustainable chemical treatment against H. armigera infestation.

Baseline susceptibility of Helicoverpa armigera, Plutella xylostella, and Spodoptera frugiperda to the meta-diamide insecticide broflanilide

Broflanilide is a novel meta-diamide insecticide that acts as a γ-aminobutyric acid-gated chloride channel allosteric modulator. With its unique mode of action, broflanilide has no known cross-resistance with existing insecticides and is expected to be an effective tool for the management of insecticide resistance. Establishing the baseline susceptibility to this insecticide is an essential step for developing and implementing effective resistance management strategies. Here we evaluated the baseline susceptibility to broflanilide for 3 cosmopolitan lepidopteran pest species, Helicoverpa armigera, Plutella xylostella, and Spodoptera frugiperda. Broflanilide exhibited high activity against populations sampled in the major distribution range of these pests in China, with median lethal concentrations (LC₅₀ ) ranging between 0.209 and 0.684, 0.076 and 0.336, and 0.075 and 0.219 mg/L for H. armigera, P. xylostella, and S. frugiperda, respectively. Among-population variability in susceptibility to broflanilide was moderate for H. armigera (3.3-fold), P. xylostella (4.4-fold), and S. frugiperda (2.9-fold). The recommended diagnostic concentrations for H. armigera, P. xylostella, and S. frugiperda were 8, 4, and 2 mg/L, respectively. Little or no cross-resistance to broflanilide was detected in 3 diamide-resistant strains of P. xylostella and 1 spinosyns-resistant strain of S. frugiperda. Our results provide critical information for the development of effective resistance management programs to sustain efficacy of broflanilide against these key lepidopteran pests.

Helicoverpa genus on the edge of the continental U.S.: Flight phenology, analysis of hybrid presence, and insecticide performance in high-input field crops in Puerto Rico

The genus Helicoverpa includes several agricultural pests globally. Helicoverpa armigera was reported in several countries in South America in 2013, and in Puerto Rico, in 2014. This territory is considered an agricultural hub, with a high-input system of seed production in the southern region of the island, and also at the edge of the continental U.S. Possible natural dispersion of populations of H. armigera from the Caribbean or other Central American regions poses a continuing risk to the U.S. This study was performed during the post-detection scenario of H. armigera in Puerto Rico, from 2018 to 2021. A year-round pheromone trapping program of adult males indicated an increase in the population from October to March and differences in the occurrence of Helicoverpa spp. between the municipalities Juan Diaz and Salinas. The proportion of H. armigera/H. zea and detection of congeneric hybrids between these species were assessed based on genital morphology and DNA analysis. Interestingly, neither H. armigera nor expected hybrids were detected in the present study. The susceptibility of H. zea populations to the insecticides Spinetoram, Emamectin benzoate, Chlorantraniliprole, and Esfenvalerate was assessed, and an overall significant effect of insecticide susceptibility was detected. Chlorantraniliprole and Emamectin benzoate had the highest efficacy. These results contribute to the Integrated Pest Management and Insect resistance management programs to Helicoverpa spp. in Puerto Rico. In addition, provide validated information to be considered in mitigation plans, in the scenario of an invasion of H. armigera in the continental U.S.

Regional pest suppression associated with adoption of Cry1Ac soybean benefits pest management in tropical agriculture

BACKGROUND

Bacillus thuringiensis (Bt) crops have been adopted worldwide, providing high-level protection from insect pests. Furthermore, Bt crops preserve natural enemies, promote higher yield, and economically benefit farmers. Although regional pest suppression by widespread Bt crop adoption has been observed in temperate regions, this possibility remains uncertain in tropical areas due to the high diversity of alternative hosts and mild winters.

RESULTS

Evidence of regional reduction in insecticide use across areas was observed in Brazil where Cry1Ac soybean has been grown since 2013, with up to 50% reduction in the number of insecticide sprays for managing lepidopteran pests on non-Bt soybean observed at specific locations from 2012 to 2019. Pest monitoring data from four mesoregions across 5 years of commercial plantings of Cry1Ac soybean from December 2014 to July 2019 showed reduced numbers of Chrysodeixis includens moths captured in pheromone traps across years at all locations. The number of Helicoverpa spp. moths captured also was reduced at three locations.

CONCLUSION

We provide evidence for regional suppression of lepidopteran pests and reduced insecticide use with the widespread adoption of Cry1Ac soybean in Brazil, bringing economic, social and environmental benefits. © 2022 Society of Chemical Industry.

Baseline Susceptibility and Cross-Resistance of HearNPV in Helicoverpa armigera (Lepidoptera: Noctuidae) in Brazil

The marked adoption of bioinsecticides in Brazilian agriculture in recent years is, at least partially, explained by the increasingly higher levels of insect pest resistance to synthetic insecticides. In particular, several baculovirus-based products have been registered in the last 5 years, including Helicoverpa armigera nucleopolyhedrovirus (HearNPV: Baculoviridae: Alphabaculovirus (Armigen^®)). Understanding the susceptibility of Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) to HearNPV is an important step toward development of robust Integrated Pest Management (IPM) and Insect Resistance Management programs (IRM) aimed at managing this serious insect pest. In this study, droplet feeding bioassays were used to characterize the baseline susceptibility to HearNPV (Armigen^®) in H. armigera populations collected from major soybean and cotton-growing regions in Brazil. We defined and validated a diagnostic concentration for susceptibility monitoring of H. armigera populations to HearNPV. Additionally, cross-resistance between HearNPV and the insecticides flubendiamide and indoxacarb was evaluated by testing HearNPV in a susceptible strain and in resistant strains of H. armigera to these insecticides. A low interpopulation variation of H. armigera to HearNPV was detected. The LC₅₀ values ranged from 1.5 × 10⁵ to 1.1 × 10⁶ occlusion bodies (OBs) per mL (7.3-fold variation). The mortality rate at the identified diagnostic concentration of 6.3 × 10⁸ OBs/mL, based on the calculated LC₉₉, ranged from 98.6 to 100% in populations of H. armigera collected from 2018 to 2020. No cross-resistance was detected between HearNPV and flubendiamide or indoxacarb. These results suggest that HearNPV (Armigen^®) can be an effective tool in IPM and IRM programs to control H. armigera in Brazil.

Genetic Variation and Population Structure of the Old World Bollworm Helicoverpa armigera (Hübner, 1808) (Lepidoptera: Noctuidae) in Ethiopia

Helicoverpa armigera is one of the most destructive insect pests of economically valuable crops in the world. Despite its economic importance, the population genetic structure of this insect remains unexplored in Ethiopia. To investigate the genetic diversity and population structure of H. armigera, we sampled 170 individuals from 15 populations throughout Ethiopia. We sequenced a fragment of the mitochondrial cytochrome b (cyt b) gene and five exon-primed intron-crossing (EPIC) markers. Twenty cyt b haplotypes with low-to-moderate haplotype diversity (mean Hd = 0.537) and high nucleotide diversity (mean Pi = 0.00339) were identified. The most frequently observed and widely distributed cyt b haplotype was designated as Hap_1 (67.058%), which is identical to sequences found across the globe. Tajima's D and Fu's F for the cyt b data were negative, supporting a model of population expansion. Within populations, a mean of 2.493 alleles/locus was recorded across the five EPIC loci, ranging from 1.200 to 3.600 alleles/locus. The highest mean effective number of alleles/population was 2.369 and the lowest was 1.178. The mean observed heterozygosity (HO) of the five loci (0-0.289; mean 0.104 ± 0.020) was lower than the expected heterozygosity (HE) (0.095-0.523; mean 0.258 ± 0.028). AMOVA detected significant genetic structure with 61% of the total molecular genetic variation of EPIC genotypes occurring between populations, suggesting a considerable degree of differentiation among populations. STRUCTURE analyses clustered the H. armigera populations into three distinct population groups but very low isolation by distance (R2 = 0.0132, P < 0.05).

The Micrococcus luteus infection activates a novel melanization pathway of cSP10, cSP4, and cSP8 in Helicoverpa armigera

Melanization is a key immune response mediated by serine protease (SP) cascade in insects. Multiple SP pathways exist in different species and it is unclear how conserved these cascades are. The cotton bollworm Helicoverpa armigera is a major worldwide agricultural pest. We reported a conserved melanization pathway in this species, which consists of SP41, cSP1, and cSP6. In this study, we attempted to identify an insect pathogen that elicits the cascade and test whether or not there are other SP cascades in H. armigera. After Micrococcus luteus, Enterobacter cloacae, Beauveria bassiana, or Helicoverpa armigera nucleopolyhedrovirus were injected into larvae, pathogen-induced hemolymph samples were collected for in vitro biochemical assays, which failed to detect proSP41 or procSP1 activation. In contrast, we found that procSP4, a protein proposed to participate in H. armigera melanization, was activated in M. luteus infected hemolymph. We further revealed that cSP8 was a prophenoloxidase (PPO) activating protease downstream of cSP4, and cSP4 was activated by cSP10. The pathway of cSP10-cSP4-cSP8 activated PPO in vitro. Efficiently cleaved procSPH11 and procSPH50 by cSP8 substantially enhanced phenoloxidase activity, suggesting they work together as a cofactor for cSP8 mediated PPO activation. Hemolymph from larvae challenged with M. luteus or its peptidoglycan effectively activated procSP10. Collectively, these results revealed a new PPO activation cascade specifically triggered by the bacterium. In addition, we found that the PPO activation cascades in H. armigera and Manduca sexta are conserved.

Efficacy of Biopesticides in the Management of the Cotton Bollworm, Helicoverpa armigera (Noctuidae), under Field Conditions

Simple Summary

Cotton remains the most important cash crop in the world. The key insect pests of cotton include the African bollworm Helicoverpa armigera. This pest causes damage to crops estimated at greater than USD 2 billion per year worldwide. Excessive use of insecticides to control this pest has a negative effect on the environment, and is expensive for the farmers. The aim of this study is to explore the field efficacy of different biopesticides as an alternative to control H. armigera. Four biopesticides—namely, Eco-Bb^® (Beauveria bassiana), Bb endophyte (Beauveria bassiana), Bolldex^® (nucleopolyhedrovirus), and Delfin^® (Bacillus thuringiensis)—were evaluated and compared with the pyrethroid Karate^® (lambda-cyhalothrin) and an untreated control. Plots treated with Karate^® had significantly lower numbers of H. armigera larvae compared to the untreated control, and were comparable to the plots treated with Bolldex^®. On average, plots treated with Bolldex^® had a high seed cotton yield compared to the other treatments. Biopesticides showed a moderate reduction in the numbers of H. armigera larvae, and could thus be used within an integrated pest management programme.

Abstract

Cotton is one of the most valuable materials in the world, popularly used in the clothing industry and other products. However, its production is limited by the high infestation of insect pests. A study was conducted to evaluate the effects of different biopesticides on the control of the African bollworm (Helicoverpa armigera) under cotton field conditions. Four biopesticides—namely, Eco-Bb^® (Beauveria bassiana), Bb endophyte (Beauveria bassiana), Bolldex^® (Nucleopolyhedrovirus), and Delfin^® (Bacillus thuringiensis)—were evaluated and compared with the pyrethroid Karate^® (lambda-cyhalothrin) and an untreated control against H. armigera. Field trials were conducted at the Agriculture Research Council, Rustenburg, in the North West Province of South Africa during the 2017 and 2018 cotton seasons. The results revealed that in plots sprayed with Karate^® and Bolldex^®, the numbers of H. armigera were significantly reduced compared to the untreated controls. Plots treated with Bolldex^® had the lowest number of damaged bolls in 2017, while those treated with Karate^® had the lowest number of damaged bolls in 2018. All treated plots had significantly fewer damaged bolls when compared to the controls. A seed cotton yield of 5987 kg/ha was recorded in the plots that were treated with Bolldex^®—significantly higher than the yields from plots treated with Eco-Bb^®, Delfin^®, and Bb endophyte—in 2017. However, the yield in treatments with Eco-Bb^®, Delfin^®, and Bb endophyte was lower than that from the untreated controls during this season. In 2018, plots treated with Bolldex^® had the highest yield, at 6818 kg/ha, which was not different from the other treatments. The highest average seed cotton yield of 6400 kg/ha was recorded in the plots treated with Bolldex^®, followed by Karate^®. In summary, the efficacy of different biopesticides against H. armigera varied significantly, while the synthetic pesticide (Karate^®) and Bolldex^® resulted in more consistent control of this pest. The results suggest that biopesticides may, however, have the potential for use in the sustainable control of cotton bollworms as part of integrated pest management programmes, although further work is required to support this hypothesis.

Transcriptional Analysis of Cotton Bollworm Strains with Different Genetic Mechanisms of Resistance and Their Response to Bacillus thuringiensis Cry1Ac Toxin

Transgenic crops producing Bacillus thuringiensis (Bt) insecticidal proteins are grown widely for pest control, but the evolution of resistance in target pests could reduce their efficacy. Mutations in genes encoding cadherin, ABC transporter or tetraspanin were linked with resistance to Cry1Ac in several lepidopteran insects, including the cotton bollworm (Helicoverpa armigera), a worldwide agricultural pest. However, the detailed molecular mechanisms by which these mutations confer insect resistance to Cry1Ac remain largely unknown. In this study, we analyzed the midgut transcriptomes of a susceptible SCD strain and three SCD-derived Cry1Ac-resistant strains of H. armigera (SCD-r1, with a naturally occurring deletion mutation of cadherin; SCD-KI, with a knock-in T92C point mutation in tetraspanin; and C2/3-KO, with both ABCC2 and ABCC3 knocked out). Evaluation of midgut transcript profiles of the four strains without Cry1Ac exposure identified many constitutively differentially expressed genes (DEGs) in the resistant SCD-r1 (n = 1355), SCD-KI (n = 1254) and C2/3-KO (n = 2055) strains. Analysis of DEGs in the midguts of each strain after Cry1Ac exposure revealed similar patterns of response to Cry1Ac in the SCD and SCD-r1 strains, but unique responses in the SCD-KI and C2/3-KO strains. Expression of midgut epithelium healing and defense-related genes was strongly induced by Cry1Ac intoxication in the SCD and SCD-r1 strains, while immune-related pattern recognition receptor and effector genes were highly expressed in the SCD-KI strain after Cry1Ac exposure. This study advances our knowledge of the transcriptomic basis for insect resistance to Bt toxins and provides a valuable resource for further molecular characterization of insect response to Cry1Ac toxin in H. armigera and other pest species.

Genetic diversity and demographic history of the Old World Bollworm, Helicoverpa armigera (Hubner) (Lepidoptera: Noctuidae), in Ethiopia inferred from mitochondrial gene sequences

The Old World bollworm, Helicoverpa armigera (Hubner) (Lepidoptera: Noctuidae), is a globally distributed agricultural and horticultural insect pest. Despite the economic importance of this insect in Ethiopia, its genetic diversity and demographic history are poorly understood. We examined the nucleotide variation of the mitochondrial cytochrome c oxidase subunit I (COI) gene fragment of 74 H. armigera individuals from six collection sites in Ethiopia. We recorded 15 COI haplotypes in H. armigera, ten globally shared and five exclusive to Ethiopia (HaET15, HaET14, HaET10, HaET7, and HaET4). Haplotype HaET1 was the most widely geographically distributed and frequent (71.62%). Analysis of molecular variance (AMOVA) revealed a high and significant level of variation within H. armigera populations (θ_ST = −0.0135). Negative values of the neutrality test and nonsignificant index of mismatch distribution supported the demographic expansion of H. armigera populations in Ethiopia; furthermore, this was also supported by the nonsignificant values of the sum of squared deviations (SSD) and raggedness index (r). The high genetic variation and population expansion of H. armigera have immense implications for devising locally adapted management strategies in area‐wide integrated pest management IPM programs. However, a comprehensive study of H. armigera genetic diversity and population structure using various molecular markers is needed for future confirmation.

Global population genomic signature of Spodoptera frugiperda (fall armyworm) supports complex introduction events across the Old World

Native to the Americas, the invasive Spodoptera frugiperda (fall armyworm; FAW) was reported in West Africa in 2016, followed by its chronological detection across the Old World and the hypothesis of an eastward Asia expansion. We explored population genomic signatures of American and Old World FAW and identified 12 maternal mitochondrial DNA genome lineages across the invasive range. 870 high-quality nuclear single nucleotide polymorphic DNA markers identified five distinct New World population clusters, broadly reflecting FAW native geographical ranges and the absence of host-plant preferences. We identified unique admixed Old World populations, and admixed and non-admixed Asian FAW individuals, all of which suggested multiple introductions underpinning the pest’s global spread. Directional gene flow from the East into eastern Africa was also detected, in contrast to the west-to-east spread hypothesis. Our study demonstrated the potential of population genomic approaches via international partnership to address global emerging pest threats and biosecurity challenges.

This population genomics study identifies the complex multiple introduction history of Spodoptera frugiperda (fall armyworm) from the Americas, into Africa and Asia. This provides new insight into the ‘east-to-west’ directionality of gene flow, and suggests ample genomic exchange at the nuclear level.

Helicoverpa armigera and Helicoverpa zea hybridization: constraints, heterosis, and implications for pest management

BACKGROUND

The invasion of Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) into the New World has made it possible for this pest to hybridize with a native American species, H. zea (Boddie), under natural conditions. We investigated the viability and development of hybrids of these two Helicoverpa species. We reared the parental species and evaluated crosses between H. armigera males and H. zea females and vice versa, two intercrosses between hybrids, and eight backcrosses between hybrids and parental species. We estimated the length of immature stages, fecundity, survival, sex ratio, and heterosis.

RESULTS

Although hybridization occcurred, with heterosis during the development of immatures, reproductive incompatibilities also were observed between the parental species and between hybrids from subsequent crosses. The interspecific crosses between hybrids and backcrosses confirmed the possibility of introgression events and their perpetuation in field populations. The results indicate that hybridization events are favored at high population levels, while at low population levels the 'species identities' will be maintained.

CONCLUSIONS

The possibility of interspecific gene flow and its perpetuation through successive crosses and backcrosses suggests several recommenations for management. Populations of both species should be maintained at an equilibrium level to reduce the chance of interspecific crosses, which are presumably more likely to occur during pest outbreaks. The existence of hybridization and resistance to different active pesticide ingredients should be monitored. All practices related to managing the resistance of these pests to chemical and biological insecticides should be systematized to reduce the chance of selecting for resistant individuals.

Balancing nutrients in a toxic environment: the challenge of eating

Insect herbivores can regulate their food intake by mixing food sources with different nutrient content, but face the resulting challenge of ingesting various plant secondary metabolites. How insects deal with toxins in a complex nutrient environment is unclear. Here we investigated the influence of a classic plant secondary metabolite, allyl glucosinolate (sinigrin), and its hydrolyzed product allyl isothiocyanate (AITC), on the development of Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) when fed on diets with different protein-to-carbohydrate (p : c) ratios. We also examined the effects of these toxins on larval biochemistry, by chemically analyzing the frass produced by insects feeding on the different diets. As expected, AITC had a greater negative effect than sinigrin on H. armigera life-history traits. However, AITC at low concentration appeared to have a positive effect on some traits. Both sinigrin and AITC-induced detoxification activity in the gut, and the reaction was related to diet protein concentration. High-protein diets can provide the required free amino acid, especially cysteine, needed for the detoxification process. The nutrient content of the diet influences how plant secondary metabolites are handled, and the use of artificial diets in experiments investigating the metabolic fate of plant secondary compounds needs to be carefully evaluated.

Population genomics provides insights into lineage divergence and local adaptation within the cotton bollworm

The cotton bollworm Helicoverpa armigera is a cosmopolitan pest and its diverse habitats plausibly contribute to the formation of diverse lineages. Despite the significant threat it poses to economic crops worldwide, its evolutionary history and genetic basis of local adaptation are poorly understood. In this study, we de novo assembled a high-quality chromosome-level reference genome of H. a. armigera (contig N50 = 7.34 Mb), with 99.13% of the HaSCD2 assembly assigned into 31 chromosomes (Z-chromosome + 30 autosomes). We constructed an ultra-dense variation map across 14 cotton bollworm populations and identified a novel lineage in northwestern China. Historical inference showed that effective population size changes coincided with global temperature fluctuation. We identified nine differentiated genes in the three H. armigera lineages (H. a. armigera, H. a. conferta, and the new northwestern Chinese lineage), of which per and clk genes are involved in circadian rhythm. Selective sweep analyses identified a series of GO categories related to climate adaptation, feeding behavior and insecticide tolerance. Our findings reveal fundamental knowledge of the local adaptation of different cotton bollworm lineages and will guide the formulation of cotton bollworm management measures at different scales.

Determinants of Insecticide Resistance Evolution: Comparative Analysis Among Heliothines

It is increasingly clear that pest species vary widely in their propensities to develop insecticide resistance. This review uses a comparative approach to analyze the key pest management practices and ecological and biochemical or genetic characteristics of the target that contribute to this variation. We focus on six heliothine species, three of which, Helicoverpa armigera, Heliothis virescens, and Helicoverpa zea, have developed resistances to many pesticide classes. The three others, Helicoverpa punctigera, Helicoverpa assulta, and Helicoverpa gelotopoeon, also significant pests, have developed resistance to very few pesticide classes. We find that host range and movement between alternate hosts are key ecological traits that influence effective selection intensities for resistance. Operational issues are also critical; area-wide, cross-pesticide management practices that account for these ecological factors are key to reducing selection intensity. Without such management, treatment using broad-spectrum chemicals serves to multiply the effects of host plant preference, preadaptive detoxification ability, and high genetic diversity to create a pesticide treadmill for the three high-propensity species.Without rigorous ongoing management, such a treadmill could still develop for newer, more selective chemistries and insecticidal transgenic crops.

Involvement of CYP2 and mitochondrial clan P450s of Helicoverpa armigera in xenobiotic metabolism

Insect CYP2 and mitochondrial clan P450s are relatively conserved genes encoding enzymes generally thought to be involved in biosynthesis or metabolism of endobiotics. However, emerging evidence argues they have potential roles in chemical defense as well, but their actual detoxification functions remain largely unknown. Here, we focused on the full complement of 8 CYP2 and 10 mitochondrial P450s in the generalist herbivore, Helicoverpa armigera. Their varied spatiotemporal expression profiles were analyzed and reflected their specific functions. For functional study of the mitochondrial clan P450s, the redox partners, adrenodoxin reductase (AdR) and adrenodoxin (Adx), were identified from genomes of eight insects and an efficient in vitro electron transfer system of mitochondrial P450 was established by co-expression with Adx and AdR of H. armigera. All CYP2 clan P450s and 8 mitochondrial P450s were successfully expressed in Sf9 cells and compared functionally. In vitro metabolism assays showed that two CYP2 clan P450s (CYP305B1 and CYP18A1) and CYP333B3 (mito clan) could epoxidize aldrin to dieldrin, while CYP305B1 and CYP339A1 (mito clan) have limited but significant hydroxylation capacities to esfenvalerate. CYP303A1 of the CYP2 clan exhibits high metabolic efficiency to 2-tridecanone. Screening the xenobiotic metabolism competence of CYP2 and mitochondrial clan P450s not only provides new insights on insect chemical defense but also can give indications on their physiological functions in H. armigera and other insects.

Field-evolved resistance to 11 insecticides and the mechanisms involved in Helicoverpa armigera (Lepidoptera: Noctuidae)

BACKGROUND

To understand the ongoing resistance of cotton bollworm, Helicoverpa armigera, the sensitivity of five field populations to commonly used insecticides, indoxacarb, abamectin, methoxyfenozide, chlorfenapyr, chlorantraniliprole, spinetoram, lambda-cyhalothrin, carbosulfan, metaflumizone, chlorpyrifos, and flufenoxuron, were evaluated. Furthermore, the biochemical and molecular mechanisms of field-evolved resistance in H. armigera were also investigated.

RESULTS

Five field populations of H. armigera showed moderate resistance to indoxacarb, chlorantraniliprole, metaflumizone, methoxyfenozide, carbosulfan and lambda-cyhalothrin. The resistance ratio (RR) of indoxacarb was significantly correlated with glutathione-S-transferases (GSTs) activity (r = 0.913, P = 0.011). Methoxyfenozide RR was largely correlated with cytochrome P450s activity (r = 0.860, P = 0.028). Besides, six cytochrome P450s genes of CYP4L5 in AQP, CYP6B7 and CYP9A14 in HDP and BDP, CYP9A17V2 in HDP and YSP, CYP332A1 in HDP, LFP, AQP and YSP, CYP337B1 in YSP, and two GSTs genes of GSTd1 and GSTs1 in HDP were overexpressed (>5-fold). Moreover, indoxacarb RR was positively correlated with the overexpression of GSTs1, GSTd1 and CYP9A14 genes (r = 0.880, 0.98 and 0.86, P = 0.021, 0.001 and 0.028, respectively). The transcript of CYP9A17V2 and CYP337B1 were found to be correlated with metaflumizone RR (r = 0.950, P = 0.004) and carbosulfan RR (r = 0.850, P = 0.033), respectively.

CONCLUSION

H. armigera can be effectively controlled using abamectin, chlorfenapyr, chlorpyrifos and spinetoram in Hebei and Shandong provinces. The present study demonstrated that the relative expression level of GSTs1, GSTd1, CYP9A14, CYP9A17V2 and CYP337B1 genes were significantly correlated with the resistance ratio to indoxacarb, metaflumizone and carbosulfan in field H. armigera.

Identification of Bacillus thuringiensis Strains for the Management of Lepidopteran Pests

Bacillus thuringiensis (Bt)-based bioinsecticides and transgenic plants expressing proteins with insecticidal activity (Cry and Vip) have been successfully used in several integrated pest management programs worldwide. Lepidoptera comprise some of the most economically important insect pests of the major agricultural crops. In this study, the toxicity of 150 Bt strains was evaluated against Helicoverpa armigera (Hübner) larvae. Eight strains (426, 520B, 1636, 1641, 1644, 1648, 1657 and 1658) showed high insecticide activity against H. armigera and were therefore tested against Anticarsia gemmatalis (Hübner), Spodoptera cosmioides (Walker), Chrysodeixis includens (Walker), and Diatraea saccharalis (Fabricius) larvae. Our results showed that most of the Bt strains were also toxic to these lepidopteran species. The biochemical and molecular analyses of these strains revealed that they had a similar protein profile; however, their cry and vip gene contents were variable. In addition, the median lethal concentration (LC₅₀) of the selected strains indicated that the strains 1636, 1641, and 1658 were the most effective against H. armigera, showing LC₅₀ values of 185.02, 159.44, and 192.98 ng/cm², respectively. Our results suggest that the selected Bt strains have great potential to control the lepidopteran pests H. armigera, A. gemmatalis, D. saccharalis, S. cosmioides, and C. includes.

Assay Optimization Can Equalize the Sensitivity of Real-Time PCR with ddPCR for Detection of Helicoverpa armigera (Lepidoptera: Noctuidae) in Bulk Samples

Simple Summary

Invasive species are a constant threat to agriculture throughout the world against which early detection is one of the primary defenses. The Old World bollworm is one of the most important invasive agricultural pests in the world. While historically absent from the Americas, this species was first found in South America in 2013 and poses an ongoing threat of spreading into North America. Surveys are conducted each year, which result in hundreds or thousands of traps that must be screened for this species. Unfortunately, the most common non-target is the native corn earworm, which is nearly identical morphologically to the Old World bollworm and cannot be easily separated. Molecular methods have been developed to screen these trap samples, but the required equipment is expensive and not commonly available. This study details improvements to current molecular methods that will allow for screening of bulk trap samples using standard laboratory instruments and protocols. The ability to perform these methods in nearly any molecular biology lab will greatly enhance our ability to detect and exclude this important pest.

Abstract

Helicoverpa armigera (Hübner) is one of the most important agricultural pests in the world. This historically Old World species was first reported in Brazil in 2013 and has since spread throughout much of South America and into the Caribbean. Throughout North America, H. armigera surveys are ongoing to detect any incursions. Each trap is capable of capturing hundreds of native Helicoverpa zea (Boddie). The two species cannot be separated without genitalic dissection or molecular methods. A ddPCR assay is currently used to screen large trap samples, but this equipment is relatively uncommon and expensive. Here, we optimized a newly designed assay for accurate and repeatable detection of H. armigera in bulk samples across both ddPCR and less costly, and more common, real-time PCR methods. Improvements over previously designed assays were sought through multiple means. Our results suggest bulk real-time PCR assays can be improved through changes in DNA extraction and purification, so that real-time PCR can be substituted for ddPCR in screening projects. While ddPCR remains a more sensitive method for detection of H. armigera in bulk samples, the improvements in assay design, DNA extraction, and purification presented here also enhance assay performance over previous protocols.

Saltational evolution of a pesticide-metabolizing cytochrome P450 in a global crop pest

BACKGROUND

The cotton bollworm, Helicoverpa armigera (Hübner), is a damaging insect pest threatening agricultural crops worldwide as a result of its resistance to insecticides. Metabolic resistance to pyrethroid insecticides is conferred by the chimeric P450 enzyme CYP337B3, produced by unequal crossing-over between CYP337B1 and CYP337B2. CYP337B3 is 99.7% similar to CYP337B1 except for the 177 N-terminal amino acids (AAs) containing the substrate recognition site 1 from CYP337B2. Here, we studied the structure-function relationship of CYP337B3 and CYP337B1 to determine the AAs that enable CYP337B3 to efficiently hydroxylate the 4'-carbon position of fenvalerate, which neither CYP337B1 nor CYP337B2 can do.

RESULTS

Site-directed mutagenesis showed that the L114F substitution in CYP337B3 reduced its 4'-hydroxylation activity by 89%, but the reciprocal F114L substitution in CYP337B1 increased its 4'-hydroxylation activity to only 49% of the level of CYP337B3. Docking models showed that AA 114 seems to have different functions in CYP337B1 and CYP337B3. Antibodies detected two- to three-fold more CYP337B1 than CYP337B3 in larval cuticle, which along with a 49% 4'-hydroxylation activity increase due to a F114L substitution in vivo might be expected to provide as much protection for the larva against exposure to fenvalerate as CYP337B3. However, CYP337B3 is present at much higher frequencies than CYP337B1-CYP337B2 in most populations, including those recently invading South America.

CONCLUSION

The metabolic resistance to pyrethroids in H. armigera has evolved by saltational evolution - by a single mutation, an unequal crossing-over, producing a larger selective advantage than could be attained gradually by stepwise improvement of the parental enzyme. © 2021 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

HearNPV susceptibility in Helicoverpa armigera and Helicoverpa punctigera strains resistant to Bt toxins Cry1Ac, Cry2Ab, and Vip3Aa

Genetically engineered crops expressing insecticidal toxins from Bacillus thuringiensis (Bt) have improved the management of targeted lepidopteran pests and reduced the use of insecticide sprays. These benefits explain an increasing adoption of Bt crops worldwide, intensifying the selection pressure on target species and the risk of resistance. Nucleopolyhedroviruses (NPVs) are effective bioinsecticides against numerous important lepidopteran pests. If Bt-resistant insects are shown to be susceptible to NPVs then these bioinsecticides could be a valuable component of Insecticide Resistance Management (IRM) strategies for Bt crops. We assessed the effectiveness of a Helicoverpa nucleopolyhedrovirus (HearNPV) against several different Bt-resistant strains. Utilising a droplet feeding bioassay we confirmed susceptibility to HearNPV in Helicoverpa punctigera and Helicoverpa armigera larvae resistant to the Bt toxins Cry1Ac, Cry2Ab, and Vip3A. Dual resistant H. punctigera, (Cry1Ac/Cry2Ab, and Cry2Ab/Vip3A) and dual resistant H. armigera (Cry2Ab/Vip3A) were also susceptible to HearNPV. Regardless of their specific resistance profile, Bt-resistant larvae displayed statistically similar lethal concentration (LC₅₀) and lethal time (LT₅₀) responses to HearNPV when compared to Bt-sensitive control insects. These results indicate that Bt-resistant H. armigera and H. punctigera are not cross-resistant to HearNPV. Consequently, the use of HearNPV against these pests may be a valuable tool to an IRM strategy for controlling Bt-resistant populations.

Helicoverpa armigera Harm 1 Haplotype Predominates in the Heliothinae (Lepidoptera: Noctuidae) Complex Infesting Tomato Crops in Brazil

Tomato (Solanum lycopersicum L.) is a natural host for the Helicoverpa-Chloridea (Lepidoptera: Noctuidae: Heliothinae) pest complex. The species Helicoverpa armigera (Hübner) was responsible for significant yield losses in several crops after its detection in Brazil. The morphology of its larval stage resembles common Heliothinae species, making pest control decisions difficult. The overall lack of studies on the Heliothinae associated with tomatoes in Brazil and the establishment of H. armigera in the country plus their recent outbreaks supported our investigation about the relative importance of the insects from the Helicoverpa-Chloridea complex in this vegetable crop. A nationwide survey was carried out across fresh-market and processing tomato fields. Molecular analyses targeting a segment of the mitochondrial cytochrome oxidase subunit I (mtCOI) gene and their sequence analyses indicated the presence of a pest complex, comprising the introduced species H. armigera and the indigenous species, Helicoverpa zea (Boddie), and Chloridea virescens (Fabricius). The Harm 1 haplotype of H. armigera was identified as the predominant Heliothinae pest infesting fresh-market tomatoes. The New World species Chloridea subflexa (Guenée) as well as the exotic Solanaceae-specific species Helicoverpa assulta (Guenée) were not found in our survey. Additional larvae surveys in processing tomato fields during 2013/2014 in Central Brazil also indicated H. armigera as the most abundant Heliothinae species (95%) together with H. zea (4.75%) and C. virescens (0.25%). The occurrence of distinct Helicoverpa species (which are potentially capable of interbreeding) indicates that novel crop management strategies will be necessary in order to minimize damages caused by this pest complex in tomatoes.

Host plant use of Helicoverpa spp. (Lepidoptera: Noctuidae) in the Brazilian agricultural landscape

BACKGROUND

The Old-World bollworm, Helicoverpa armigera (Hübner), was recently documented attacking cotton and soybean plants in Brazil; however, restricted basic knowledge on host plant interactions and landscape use in Brazil have limited the effectiveness of control measures. In this study, we evaluated the suitability of different crops commonly cultivated in Brazil as hosts for H. armigera and H. zea, and examined their contribution to the establishment and size of H. armigera and H. zea field populations. We also estimated the proportions of H. armigera and H. zea moths that used cotton, noncotton C₃ plants, and C₄ plants as hosts in four regions in Brazil through the length of the cropping season.

RESULTS

Viability of H. armigera larvae was highest on cotton (46.1%), followed by millet (39.5%), sorghum (31.2%), soybean (24.2%), and maize (21.1%). Noncotton C₃ hosts served as the major source of H. armigera moths in all regions evaluated, and C₄ hosts were a source of H. armigera mainly in regions where winter maize is typically cultivated. H. armigera moths that used cotton plants as natal hosts were observed during the reproductive stage of the crop mainly in the state of Bahia. Only C₄ host plants were a consistent source of H. zea moths, primarily when maize was in the reproductive stage. H. armigera individuals were the main species infesting cotton and soybean fields while H. zea individuals were the main species infesting maize ears.

CONCLUSIONS

Regional differences in the host use and population dynamics of H. armigera among the regions evaluated may be attributed to variation in alternative host utilization (crops, noncrops, and weeds) and the possible occurrence of facultative diapause and or migration.

Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) in Brazil: the Big Outbreak Monitored by Light Traps

The first detection of Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) in Brazil pointed to a gloomy future for South American agriculture in the 2012/2013 harvest, and insecticide sales increased exponentially during 2013 and 2014. However, after this outbreak, the population of this insect returned to manageable levels. This study documents data on H. armigera moth collection using light traps during the outbreak in two locations: (a) western region of the state of Bahia, including population levels of H. armigera and main noctuid pests during the big outbreak (February and March 2013); (b) Federal District, including monthly data for five growing seasons (July 2012-June 2017). During the outbreak, an average of 527.3 moths were collected per trap (cotton crop, March) in the western region of Bahia each night, while the maximum average in the Federal District was 75.4 moths (January). The number of moths decreased in the following growing seasons, and in October 2016, the maximum number was 2.8 moths per trap. Aspects related to the variations of H. armigera and Helicoverpa zea (Boddie) populations, including the study of phenology and relationship with climatic factors and Oceanic Niño Index, were analyzed and discussed. All aspects are approached to contribute to the management of lepidopteran pests, especially H. armigera, in the productive systems of the Brazilian Cerrado.

Roles of the variable P450 substrate recognition sites SRS1 and SRS6 in esfenvalerate metabolism by CYP6AE subfamily enzymes in Helicoverpa armigera

The cotton bollworm P450s of the clustered CYP6AE subfamily share high sequence identities but differ dramatically in their capacity to metabolize xenobiotics, especially esfenvalerate. Among them, CYP6AE17 has the highest sequence identity with CYP6AE18 but shows ~7-fold higher metabolic efficiency. CYP6AE11 is most active towards esfenvalerate but CYP6AE20 is inactive even though the enzymes share 54.8% sequence identity. Sequence analysis revealed the SRS1 (Substrate Recognition Site) and SRS6 between CYP6AE17 and CYP6AE18, and SRS1 between CYP6AE11 and CYP6AE20 are the most variable among all six SRSs. In order to identify the key factors that underlie the observed catalytic difference, we exchanged these SRS sequences between two pairs of P450s and studied the activity of the resulting hybrid mutants or chimeras. In vitro metabolism showed that the CYP6AE17/18 chimeras had 2- and 14-fold decreased activities and the CYP6AE18/17 chimeras had 6- and 10-fold increased activities to esfenvalerate. Meanwhile, after exchanging SRS1 with each other, the CYP6AE11/20 chimera folded incorrectly but the CYP6AE20/11 chimera gained moderate activity to esfenvalerate. Molecular modelling showed that amino acids variants within SRS1 or SRS6 change the shape and chemical environment of the active sites, which may affect the ligand-binding interactions. These results indicate that the protein structure variation resulting from the sequence diversity of SRSs promotes the evolution of insect chemical defense and contributes to the development of insect resistance to pesticides.