Death-Associated LIM-Only Protein Reduces Cry1Ac Toxicity by Sequestration of Cry1Ac Protoxin and Activated Toxin in Helicoverpa armigera.

The extensive use of Bacillus thuringiensis (Bt) in pest management has driven the evolution of pest resistance to Bt toxins, particularly Cry1Ac. Effective management of Bt resistance necessitates a good understanding of which pest proteins interact with Bt toxins. In this study, we screened a Helicoverpa armigera larval midgut cDNA library and captured 208 potential Cry1Ac-interacting proteins. Among these, we further examined the interaction between Cry1Ac and a previously unknown Cry1Ac-interacting protein, HaDALP (H. armigera death-associated LIM-only protein), as well as its role in toxicology. The results revealed that HaDALP specifically binds to both the Cry1Ac protoxin and activated toxin, significantly enhancing cell and larval tolerance to Cry1Ac. Additionally, HaDALP was overexpressed in a Cry1Ac-resistant H. armigera strain. These findings reveal a greater number of Cry1Ac-interacting proteins than previously known and demonstrate, for the first time, that HaDALP reduces Cry1Ac toxicity by sequestering both the protoxin and activated toxin.

Dual-role regulator of a novel miR-3040 in photoperiod-mediated wing dimorphism and wing development in green peach aphid.

Wing dimorphism is regarded as an important phenotypic plasticity involved in the migration and reproduction of aphids. However, the signal transduction and regulatory mechanism of wing dimorphism in aphids are still unclear. Herein, the optimal environmental conditions were first explored for inducing winged offspring of green peach aphid, and the short photoperiod was the most important environmental cue to regulate wing dimorphism. Compared to 16 L:8 D photoperiod, the proportion of winged offspring increased to 90% under 8 L:16 D photoperiod. Subsequently, 5 differentially expressed microRNAs (miRNAs) in aphids treated with long and short photoperiods were identified using small RNA sequencing, and a novel miR-3040 was identified as a vital miRNA involved in photoperiod-mediated wing dimorphism. More specifically, the inhibition of miR-3040 expression could reduce the proportion of winged offspring induced by short photoperiod, whereas its activation increased the proportion of winged offspring under long photoperiod. Meanwhile, the expression level of miR-3040 in winged aphids was about 2.5 times that of wingless aphids, and the activation or inhibition of miR-3040 expression could cause wing deformity, revealing the dual-role regulator of miR-3040 in wing dimorphism and wing development. In summary, the current study identified the key environmental cue for wing dimorphism in green peach aphid, and the first to demonstrate the dual-role regulator of miR-3040 in photoperiod-mediated wing dimorphism and wing development.

Balancing metabolism and reproduction.

The bacterium responsible for a disease that infects citrus plants across Asia facilitates its own proliferation by increasing the fecundity of its host insect.

Juvenile Hormone Involved in the Defensive Behaviors of Soldiers in Termite Reticulitermes aculabialis.

Eusocial insects have evolved specific defensive strategies to protect their colonies. In termite colonies, soldiers perform a colony-level defense by displaying mechanical biting, head-banging and mandible opening-closing behaviors. However, few studies have been reported on the factors modulating defensive behaviors in termites. Owing to JH (juvenile hormone) being involved in soldier differentiation, JH was speculated to affect defensive behaviors in termite soldiers. To determine the effect of JH on the defensive behaviors of termite soldiers, we performed a JHA-feeding and RaSsp1-silencing experiment and then tested the changes in defense-related behaviors, alarm pheromones and key JH signaling genes. The observed result was that after feeding workers with JHA, soldiers displayed the following: (1) decreased biting events and increased head-banging events; (2) a reduced expression of RaSsp1 and increased expression of Met (methoprene-tolerant, the nuclear receptor of JH) and Kr-h1 (the JH-inducible transcription factor Krüppel homolog 1); and (3) a decreased concentration of alarm pheromones, including α-pinene, ß-pinene and limonene (+, -). Further study showed that soldiers silenced for RaSsp1 also exhibited (1) decreased biting events and increased head-banging events and (2) increased expression of Met and Kr-h1. In addition, soldiers stimulated by the alarm pheromone limonene displayed an increase in the frequency of mandible opening-closing and biting behavior. All of these results show that JHA influenced the defensive behaviors of termite soldiers, possibly via downregulating RaSsp1 expression, up-regulating Met and Kr-h1 and stimulating the secretion of alarm pheromones, suggesting that the JH pathway plays important roles in modulating social behaviors in termite colonies.

Evolutionary analysis and biological characterization of a novel alphabaculovirus isolated from Mythimna separata.

Baculoviruses are insect-specific pathogens. Novel baculovirus isolates provide new options for the biological control of pests. Therefore, research into the biological characteristics of newly isolated baculoviruses, including accurate classification and nomenclature, is important. In this study, a baculovirus was isolated from Mythimna separata and its complete genome sequence was determined by next-generation sequencing. The double-stranded DNA genome was 153 882 bp in length, encoding 163 open reading frames. The virus was identified as a variant of Mamestra brassicae multiple nucleopolyhedrovirus (MbMNPV) and designated Mamestra brassicae multiple nucleopolyhedrovirus CHN1 (MbMNPV-CHN1) according to ultrastructural analysis, genome comparison and phylogenetic analysis. Phylogenetic inference placed MbMNPV-CHN1 in a clade containing isolates of MacoNPV-A, MacoNPV-B and MbMNPV, which we have designated the Mb-McNPV group. The genomes of isolates in the Mb-McNPV group exhibited a high degree of collinearity with relatively minor differences in the content of annotated open reading frames. The development of codon usage bias in the Mb-McNPV group was affected mainly by natural selection. MbMNPV-CHN1 shows high infectivity against seven species of Lepidoptera. The yield of MbMNPV-CHN1 in the fourth- and fifth-instar M. separata larvae was 6.25×109-1.23×1010 OBs/cadaver. Our data provide insights into the classification, host range and virulence differences among baculoviruses of the Mb-McNPV group, as well as a promising potential new baculoviral insecticide.

V-ATPase E mediates Cry2Ab binding and toxicity in Helicoverpa armigera.

Cry2Ab is one of the important alternative Bt proteins that can be used to manage insect pests resistant to Cry1A toxins and to expand the insecticidal spectrum of pyramided Bt crops. Previous studies have showed that vacuolar H+-ATPase subunits A and B (V-ATPase A and B) may be involved in Bt insecticidal activities. The present study investigated the role of V-ATPases subunit E in the toxicity of Cry2Ab in Helicoverpa amigera. RT-PCR analysis revealed that oral exposure of H. amigera larvae to Cry2Ab led to a significant reduction in the expression of H. armigera V-ATPase E (HaV-ATPase E). Ligand blot, homologous and heterologous competition experiments confirmed that HaV-ATPases E physically and specifically bound to activated Cry2Ab toxin. Heterologous expressing of HaV-ATPase E in Sf9 cells made the cell line more susceptible to Cry2Ab, whereas knockdown of the endogenous V-ATPase E in H. zea midgut cells decreased Cry2Ab's cytotoxicity against this cell line. Further in vivo bioassay showed that H. armigera larvae fed a diet overlaid with both Cry2Ab and E. coli-expressed HaV-ATPase E protein suffered significantly higher mortality than those fed Cry2Ab alone. These results support that V-ATPases E is a putative receptor of Cry2Ab and can be used to improve Cry2Ab toxicity and manage Cry2Ab resistance at least in H. armigera.

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.

Sugar starvation activates the OsSnRK1a-OsbHLH111/OsSGI1-OsTPP7 module to mediate growth inhibition of rice.

Sugar deficiency is the persistent challenge for plants during development. Trehalose-6-phosphate (T6P) is recognized as a key regulator in balancing plant sugar homeostasis. However, the underlying mechanisms by which sugar starvation limits plant development are unclear. Here, a basic helix-loop-helix (bHLH) transcription factor (OsbHLH111) was named starvation-associated growth inhibitor 1 (OsSGI1) and the focus is on the sugar shortage of rice. The transcript and protein levels of OsSGI1 were markedly increased during sugar starvation. The knockout mutants sgi1-1/2/3 exhibited increased grain size and promoted seed germination and vegetative growth, which were opposite to those of overexpression lines. The direct binding of OsSGI1 to sucrose non-fermenting-1 (SNF1)-related protein kinase 1a (OsSnRK1a) was enhanced during sugar shortage. Subsequently, OsSnRK1a-dependent phosphorylation of OsSGI1 enhanced the direct binding to the E-box of trehalose 6-phosphate phosphatase 7 (OsTPP7) promoter, thus rose the transcription inhibition on OsTPP7, then elevated trehalose 6-phosphate (Tre6P) content but decreased sucrose content. Meanwhile, OsSnRK1a degraded phosphorylated-OsSGI1 by proteasome pathway to prevent the cumulative toxicity of OsSGI1. Overall, we established the OsSGI1-OsTPP7-Tre6P loop with OsSnRK1a as center and OsSGI1 as forward, which is activated by sugar starvation to regulate sugar homeostasis and thus inhibits rice growth.

Rearing Host Dependency of Ovariole Number and Body Size in Campoletis chlorideae Uchida (Hymenoptera: Ichneumonidae).

Campoletis chlorideae has great biocontrol potential against some major noctuid pests. In order to achieve the commercial development and utilization of C. chlorideae, this study focused on the effect of rearing host species and larval instars on the ovariole number and body size of this wasp. Firstly, the morphology of the reproductive system and ovarioles of female wasps were observed. The number of ovarioles displayed great variability and asymmetry between bilateral ovaries. Moreover, the effect of four host species on ovariole number and body size of C. chlorideae were studied. The wasps had a larger ovariole number and body size when reared in Helicoverpa armigera. Additionally, the ovariole number and body size were larger when reared in the third instar larvae than in the first or second instar larvae of H. armigera. There was a strong positive correlation between the ovariole number and body size of C. chlorideae. The ovariole number and body size of the wasp could be improved under optimized artificial rearing conditions. According to these results, body size combined with ovariole number can be used as an important index to evaluate the quality of C. chlorideae. This study provides important clues for the development and application of biocontrol using C. chlorideae.

ATP Synthase Subunit α from Helicoverpa armigera Acts as a Receptor of Bacillus thuringiensis Cry1Ac and Synergizes Cry1Ac Toxicity.

Insect resistance to Bacillus thuringiensis (Bt) toxins has led to an urgent need to explore the insecticidal mechanisms of Bt. Previous studies indicated that Helicoverpa armigera ATP synthase subunit α (HaATPs-α) is involved in Cry1Ac resistance. In this study, a real-time quantitative polymerase chain reaction (RT-PCR) confirmed that HaATPs-α expression was significantly reduced in the Cry1Ac-resistant strain (BtR). Cry1Ac feeding induced the downregulated expression of HaATPs-α in the susceptible strain, but not in the BtR strain. Furthermore, the interaction between HaATPs-α and Cry1Ac was verified by ligand blotting and homologous competition experiments. The in vitro gain and loss of function analyses showed HaATPs-α involved in Cry1Ac toxicity by expressing endogenous HaATPs-α and HaATPs-α double-stranded RNAs in Sf9 and midgut cells, respectively. Importantly, purified HaATPs-α synergized Cry1Ac toxicity to H. armigera larvae. These findings provide the first evidence that HaATPs-α is a potential receptor of Cry1Ac, it shows downregulated participation in Cry1Ac resistance, and it exhibits higher enhancement of Cry1Ac toxicity to H. armigera larvae.

Involvement of an Enhanced Immunity Mechanism in the Resistance to Bacillus thuringiensis in Lepidopteran Pests.

Bacillus thuringiensis (Bt) is the safest, economically successful entomopathogen to date. It is extensively produced in transgenic crops or used in spray formulations to control Lepidopteran pests. The most serious threat to the sustainable usage of Bt is insect resistance. The resistance mechanisms to Bt toxins depend not only on alterations in insect receptors, but also on the enhancement of insect immune responses. In this work, we review the current knowledge of the immune response and resistance of insects to Bt formulations and Bt proteins, mainly in Lepidopteran pests. We discuss the pattern recognition proteins for recognizing Bt, antimicrobial peptides (AMPs) and their synthetic signaling pathways, the prophenoloxidase system, reactive oxygen species (ROS) generation, nodulation, encapsulation, phagocytosis, and cell-free aggregates, which are involved in immune response reactions or resistance to Bt. This review also analyzes immune priming, which contributes to the evolution of insect resistance to Bt, and puts forward strategies to improve the insecticidal activity of Bt formulations and manage insect resistance, targeting the insect immune responses and resistance.

Functional map of the macroglomerular complex of male Helicoverpa armigera.

The mechanism of sex pheromone reception in the male cotton bollworm Helicoverpa armigera has been extensively studied because it has become an important model system for understanding insect olfaction. However, the pathways of pheromone processing from the antenna to the primary olfactory center in H. armigera have not yet been clarified. Here, the physiology and morphology of male H. armigera olfactory sensory neurons (OSNs) were studied using single sensillum recording along with anterograde filling and intracellular recording with retrograde filling. OSNs localized in type A sensilla responded to the major pheromone component cis-11-hexadecenal, and the axonal terminals projected to the cumulus (Cu) of the macroglomerular complex (MGC). The OSNs in type B sensilla responded to the behavioral antagonist cis-9-tetradecenal, and the axonal terminals projected to the dorsomedial anterior (DMA) unit of the MGC. In type C sensilla, there were 2 OSNs: one that responded to cis-9-tetradecenal and cis-11-hexadecenol with the axonal terminals projecting to the DMA, and another that responded to the secondary pheromone components cis-9-hexadecenal and cis-9-tetradecenal with the axonal terminals projecting to the dorsomedial posterior (DMP) unit of the MGC. Type A and type B sensilla also housed the secondary OSNs, which were silent neurons with axonal terminals projected to the glomerulus G49 and DMP. Overall, the neural pathways that carry information on attractiveness and aversiveness in response to female pheromone components in H. armigera exhibit distinct projections to the MGC units.

Cyclosporin A acts as a novel insecticide against Cry1Ac-susceptible and -resistant Helicoverpa armigera.

Cotton bollworm (Helicoverpa armigera) is an economically important pest, which is difficult to manage due to its biological and ecological traits, and resistance to most insecticides. Alternative compounds for the sustainable management of H. armigera are needed. As a fungal metabolite, Cyclosporin A (CsA) has not been applied in agriculture pests. Here, CsA was evaluated as a propective insecticide for H. armigera. The results showed that CsA displayed high insecticidal activity against both Cry1Ac-susceptible and -resistant populations of H. armigera. Moreover, lower concentrations of CsA had clear effects, including significantly reduced pupal weight, pupation rate, emergence rate, ovary size, female fecundity and egg hatchability. Further study confirmed that CsA suppressed calcineurin activity and the subsequent expression of endogenous antimicrobial peptide genes (APMs), leading to impaired immunity, ultimately resulting in delayed development and increased mortality. Thus, CsA treatment could control the cotton bollworm population and even showed efficacy against those with Bt resistance. In addition, the morphological changes observed in insects fed CsA with lower concentrations provide insight into insect immunity, regulation of growth and development, regulation of body color, ovary development and sexual selection under external pressure. Overall, our study provides information on biological control potential of Cry1Ac-susceptible and -resistant populations of H. armigera to develop novel bioinsecticides.

Sublethal Effects of Thiamethoxam on Biological Traits and Detoxification Enzyme Activities in the Small Brown Planthopper, Laodelphax striatellus (Fallén).

The small brown planthopper (Laodelphax striatellus (Fallén), Hemiptera: Delphacidae), is an important agricultural pest of rice, and neonicotinoid insecticides are commonly used for controlling L. striatellus. However, the sublethal effects of thiamethoxam on L. striatellus remain relatively unknown. In this study, an age-stage life table procedure was used to evaluate the sublethal effects of thiamethoxam on the biological parameters of L. striatellus. Additionally, activities of carboxylesterase, glutathione S-transferase, and cytochrome P450 monooxygenase in the third instar nymphs were analyzed. The results indicated that the survival time of F0 adults and the fecundity of female adults decreased significantly after the third instar nymphs were treated with sublethal concentrations of thiamethoxam (LC15 0.428 mg/liter and LC30 0.820 mg/liter). The developmental duration, adult preoviposition period, total preoviposition period, and mean generation time of the F1 generation increased significantly, whereas the fecundity of the female adults, intrinsic rate of increase (ri), and finite rate of increase (λ) decreased significantly. The oviposition period was significantly shorter for the insects treated with LC30 than for the control insects. Neither sublethal concentrations had significant effects on the adult longevity, net reproduction rate (R0), or gross reproduction rate (GRR) of the F1 generation. The activities of carboxylesterase, glutathione-S-transferase, and cytochrome P450 monooxygenase increased significantly after the thiamethoxam treatments. These results indicate that sublethal concentrations of thiamethoxam can inhibit L. striatellus population growth and enhance detoxification enzyme activities.

The uncommon function and mechanism of the common enzyme glyceraldehyde-3-phosphate dehydrogenase in the metamorphosis of Helicoverpa armigera.

Glyceraldehyde-3-phosphate dehydrogenase (GAPDH), a key enzyme in glycolysis, is commonly used as an internal reference gene in humans, mice, and insects. However, the function of GAPDH in insect development, especially in metamorphosis, has not been reported. In the present study, Helicoverpa armigera and Spodoptera frugiperda ovarian cell lines (Sf9 cells) were used as materials to study the function and molecular mechanism of GAPDH in larval metamorphosis. The results showed that HaGAPDH was more closely related to GAPDH of S. frugiperda and Spodoptera litura. The transcript peaks of HaGAPDH in sixth instar larvae were 6L-3 (epidermal and midgut) and 6L-1 (fat body) days, and 20E and methoprene significantly upregulated the transcripts of HaGAPDH of larvae in qRT-PCR. HaGAPDH-GFP-His was specifically localized in mitochondria in Sf9 cells. Knockdown of HaGAPDH by RNA interference (RNAi) in sixth instar larvae resulted in weight loss, increased mortality, and decreases in the pupation rate and emergence rates. HaGAPDH is directly bound to soluble trehalase (HaTreh1) physically and under 20E treatment in yeast two-hybrid, coimmunoprecipitation, and colocalization experiments. In addition, knockdown of HaGAPDH increased the Treh1 activity, which in turn decreased the trehalose content but increased the glucose content in larvae. Therefore, these data demonstrated that GAPDH controlled the glucose content within the normal range to ensure glucose metabolism and metamorphosis by directly binding with HaTreh1.

Cyclosporin A as a Source for a Novel Insecticidal Product for Controlling Spodoptera frugiperda.

The fall armyworm (FAW), Spodoptera frugiperda, causes substantial annual agricultural production losses worldwide due to its resistance to many insecticides. Therefore, new insecticides are urgently needed to more effectively control FAW. Cyclosporin A (CsA) is a secondary metabolite of fungi; little is known about its insecticidal activity, especially for the control of FAW. In this study, we demonstrate that CsA shows excellent insecticidal activity (LC50 = 9.69 µg/g) against FAW through significant suppression of calcineurin (CaN) activity, which is a new target for pest control. Combinations of CsA and indoxacarb, emamectin benzoate, or Vip3Aa showed independent or synergistic toxicity against FAW; however, the combination of CsA and chlorantraniliprole showed no toxicity. Sublethal doses of CsA led to decreases in FAW larval and pupal weight, pupation, emergence, mating rates, adult longevity, extended development of FAW larvae and pupae and the pre-oviposition period of adults, and increases in the proportion of pupal malformation. Importantly, CsA treatment reduced FAW ovarian size and female fecundity, which suggests that it has great potential to suppress FAW colony formation. Taken together, these results indicate that CsA has high potential as an insecticide for controlling FAW.

Cyclosporin A as a Potential Insecticide to Control the Asian Corn Borer Ostrinia furnacalis Guenée (Lepidoptera: Pyralidae).

The long-term use of chemical insecticides has caused serious problems of insect resistance and environmental pollution; new insecticides are needed to solve this problem. Cyclosporin A (CsA) is a polypeptide produced by many fungi, which is used to prevent or treat immune rejection during organ transplantation. However, little is known about the utility of CsA as an insecticide. Therefore, this study evaluated the insecticidal activity of CsA using Ostrinia furnacalis as a model. The results demonstrated that CsA was toxic to O. furnacalis with LC50 values of 113.02 µg/g and 198.70 µg/g for newly hatched neonates and newly molted third-instar larvae, respectively. Furthermore, CsA treatment had sublethal effects on the development of O. furnacalis, and significantly reduced the fecundity of adults; this suggests that CsA has great potential to suppress O. furnacalis populations. Further analysis revealed that CsA suppressed calcineurin activity in larvae. CsA had independent or synergistic toxic effects on O. furnacalis when combined with ß-cypermethrin, indoxacarb, emamectin benzoate, azadirachtin, and the Bacillus thuringiensis toxin Cry1Ac, which suggests that CsA can help prevent or manage resistance. Our study provides detailed information on the potential of CsA as an insecticide for controlling lepidopterans.

Application progress of plant-mediated RNAi in pest control.

RNA interference (RNAi)-based biopesticides are novel biologic products, developed using RNAi principles. They are engineered to target genes of agricultural diseases, insects, and weeds, interfering with their target gene expression so as to hinder their growth and alleviate their damaging effects on crops. RNAi-based biopesticides are broadly classified into resistant plant-based plant-incorporated protectants (PIPs) and non-plant-incorporated protectants. PIP RNAi-based biopesticides are novel biopesticides that combine the advantages of RNAi and resistant transgenic crops. Such RNAi-based biopesticides are developed through nuclear or plastid transformation to breed resistant plants, i.e., dsRNA-expressing transgenic plants. The dsRNA of target genes is expressed in the plant cell, with pest and disease control being achieved through plant-target organism interactions. Here, we review the action mechanism and strategies of RNAi for pest management, the development of RNAi-based transgenic plant, and the current status and advantages of deploying these products for pest control, as well as the future research directions and problems in production and commercialization. Overall, this study aims to elucidate the current development status of RNAi-based biopesticides and provide guidelines for future research.

A TIL-Type Serine Protease Inhibitor Involved in Humoral Immune Response of Asian Corn Borer Ostrinia furnaculis.

To elucidate the application value of insect endogenous protease and its inhibitor genes in pest control, we analyzed in detail the transcriptome sequence of the Asian corn borer, Ostrinia furnacalis. We obtained 12 protease genes and 11 protease inhibitor genes, and comprehensively analyzed of their spatiotemporal expression by qRT-PCR. In which, a previous unstudied serine protease inhibitor gene attracted our attention. It belongs to the canonical serine proteinase inhibitor family, a trypsin inhibitor-like cysteine-rich domain (TIL)-type protease inhibitor, but its TIL domain lacks two cysteine residues, and it was named as ACB-TIL. Its expression level is relatively very low in the absence of pathogen stimulation, and can be up-regulated expression induced by Gram-negative bacteria (Escherichia coli), virus (BmNPV), and dsRNA (dsEGFP), but cannot be induced by fungus spores (Metarrhizium anisopliae). Prokaryotic expressed ACB-TIL protein can significantly inhibit the melanization in vitro. Injecting this protein into insect body can inhibit the production of antimicrobial peptides of attacin, lebocin and gloverin. Inhibition of ACB-TIL by RNAi can cause the responses of other immune-, protease- and inhibitor-related genes. ACB-TIL is primarily involved in Asian corn borer humoral immunity in responses to Gram-negative bacteria and viruses. This gene can be a potential target for pest control since this will mainly affect insect immune response.

Octopamine terminates sex pheromone biosynthesis by suppressing PBAN signal in moths.

The biosynthesis and termination of insect sex pheromones should be accurately regulated. In most moths, the biosynthesis and release of sex pheromones are regulated by a class of neuropeptides known as pheromone biosynthesis activating neuropeptides (PBANs). However, endogenous mechanisms underlying the termination of sex pheromone biosynthesis in moths remain elusive. In the present study, Helicoverpa armigera was employed as a model to investigate the role of octopamine (OA) in the inhibition of sex pheromone biosynthesis. Results demonstrated that the release of sex pheromones decreased with an increase in OA titres in older female moths. Moreover, OA treatment led to a significant decrease in sex pheromone production, female capability to attract male counterparts and subsequent female acceptance, indicating its inhibitory role in sex pheromone release. Subsequent qPCR and RNAi analyses revealed that OctßR was a key receptor of OA that regulated sex pheromone biosynthesis. In addition, the OA/OctßR signal suppressed intracellular Ca2+ levels and attenuated PBAN-mediated increase in the enzyme activities of calcineurin and acetyl-CoA carboxylase as demonstrated by OA treatment and OctßR-RNAi. Altogether, these results revealed a mechanism underlying the inhibition of sex pheromone production by OA via suppression of PBAN signalling in moths.