Developmental regulation of the pheromone biosynthesis activating neuropeptide-receptor (PBAN-R): re-evaluating the role of juvenile hormone

Prolonged Exposure to Plant Volatiles does not Significantly Affect Pban Expression and Mating Behavior in Diamondback Moth [Plutella Xylostella (Lepidoptera: Plutellidae)]

Herbivorous insects use plant volatiles to locate hosts, find food, and identify oviposition sites to aid survival and reproduction. Plant volatiles not only regulate the synthesis and release of sex pheromones in insects, but also help them in the search and orientation of sources of sex pheromones. However, after prolonged exposure to plant volatiles, the changes mediating the mating behavior of diamondback moth (DBM) [Plutella xylostella (L.) (Lepidoptera: Plutellidae)] are unclear. DBMs treated with allyl isothiocyanate, a volatile from cruciferous vegetables, did not show improved rates of mating with a limited effect on mating rhythm. This treatment inhibited mating behaviors in 3-day-old DBMs and decreased mating duration in 5-day-old DBMs. After prolonged exposure to allyl isothiocyanate, the total mating duration of DBM was not significantly different from that after prolonged exposure to n-hexane (control). The longest mating duration after emergence in DBM after prolonged exposure to allyl isothiocyanate was delayed by 1 day compared with exposure to n-hexane. Prolonged exposure to plant volatiles intensified the response behavior of DBM to sex pheromones. However, the amount of Z11-16: Ald, a major component of the sex pheromone blend exhibited no change in female pheromone glands. Pheromone biosynthesis activating neuropeptide gene (PBAN) was down-regulated in DBMs after prolonged exposure to plant volatiles. These findings suggest that prolonged exposure (6 h) to plant-derived volatiles have little effect on the mating behavior of DBM. This study provides practical guidance for applying phytochemicals in pest control by regulating insect behavior.

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 OctβR was a key receptor of OA that regulated sex pheromone biosynthesis. In addition, the OA/OctβR 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 OctβR-RNAi. Altogether, these results revealed a mechanism underlying the inhibition of sex pheromone production by OA via suppression of PBAN signalling in moths.

Suppression of PBAN receptor expression reduces fecundity in the fall armyworm, Spodoptera frugiperda

The fall armyworm, Spodoptera frugiperda, native to the tropical and subtropical areas of the American continent is one of the world's most destructive insect pests. In most insects, sex pheromone production is initiated following the activation of a pheromone-biosynthesis-activating neuropeptide (PBAN) receptor, which belongs to G protein-coupled receptor. We explored expression level of S. frugiperda PBAN receptor (Sf-PBANr) gene and validated the physiological function by assessing the fecundity of adult females subjected to its specific RNA interference (RNAi). Sf-PBANr was predicted from a transcriptome of S. frugiperda. Reverse-transcription polymerase chain reaction assay showed its expression in all developmental stages of S. frugiperda. Specific suppression of Sf-PBANr by RNAi in either sex significantly reduced the total number of laid eggs per adult female. Matings between both RNAi-treated males and female resulted in 63.3% reduction in fecundity. In contrast, the RNAi effect was less 47.5%-49.5% at the matings from single-parent RNAi treatment. These results suggest that the Sf-PBANr is associated with female of S. frugiperda.

Reinvestigation of sex pheromone biosynthesis in the moth Trichoplusiani reveals novel quantitative control mechanisms

Many species of moths have a common control mechanism for synthesizing sex pheromone: the circadian release of pheromone biosynthesis-activation neuropeptide (PBAN) that switches pheromone synthesis on/off during the day. One apparent exception to this is the noctuid moth Trichoplusia ni (Hübner), in which pheromone synthesis appears continuous through the photoperiod, with circadian release of PBAN controlling emission rate of pheromone during calling. Sex pheromone biosynthesis was reinvestigated in T. ni using stable isotope tracer-tracee and gland sampling techniques to ascertain how pheromone quantities in gland cells and on the gland cuticular surface varied and were controlled. It was found that (i) carbohydrate from adult female feeding is used to synthesize sex pheromone, (ii) most of the stored acetate ester pheromone component(s) is contained in gland cells, (iii) a large pool of pheromone is synthesized and stored through the photoperiod with a slow turnover rate, (iv) although pheromone is synthesized throughout the photoperiod, its rate can vary, influenced by release of PBAN and possibly by an unidentified head factor, with both affecting carbohydrate uptake into the acetyl CoA pheromone precursor pool, and (v) as suggested previously, PBAN also influences translocation of pheromone out of the cell to the cuticular surface, possibly by causing breakdown of intracellular lipid droplets storing pheromone molecules. This work suggests that the quantitative synthesis and emission of pheromone in T. ni, and possibly other moths, is regulated by multiple complementary biochemical mechanisms.

Calcineurin is required for male sex pheromone biosynthesis and female acceptance

Lepidoptera sex pheromone biosynthesis is regulated by pheromone biosynthesis activating neuropeptide (PBAN). PBAN regulates not only female sex pheromone biosynthesis but also male sex pheromone biosynthesis. Previous research has confirmed that PBAN regulates sex pheromone biosynthesis using Ca²⁺ as a secondary messenger in all examined species to date. However, the downstream signal of Ca²⁺ has remained elusive. In the present study, calcineurin A (CNA), a downstream signal of Ca²⁺ , was discovered in Helicoverpa armigera male hairpencil and named HaCNA. Sequence analysis demonstrated that the open reading frame of HaCNA contains 1488 nucleotides encoding 495 amino acid residues. A homology search revealed that HaCNA shares a high amino acid identity with the CNA of other insects. Developmental and spatial expression analyses revealed that the mRNA levels of HaCNA peaked at 24 h after emergence and that HaCNA expression was ubiquitous in all examined tissues. Activity analysis revealed that PBAN activates HaCNA, and a Ca²⁺ inhibitor, Lacl₃ , attenuated the effect of PBAN by decreasing HaCNA activity. Pharmacological inhibitor and RNA interference-mediated knockdown assays revealed that both activity inhibition and decreased mRNA levels of HaCNA led to a significant decrease in the production of the male sex pheromone components [octadecanol and (Z)-11 hexadecanol)] and in the efficacy of female mating acceptance. Our results demonstrate that HaCNA acts as downstream signal of PBAN/Ca²⁺ and plays an important role in PBAN-induced male sex pheromone biosynthesis and female mating acceptance.

Regulation of pheromone biosynthesis in moths

Female moths release sex pheromones for attracting males from a distance. Most moths are nocturnal so there is a periodicity to the release of sex pheromone. The temporal release of sex pheromone in most moths is regulated by calling behavior and by the biosynthesis of sex pheromone. In most moths, biosynthesis occurs in the pheromone gland and is controlled by the neuropeptide PBAN (pheromone biosynthesis activating neuropeptide). PBAN is produced in the subesophageal ganglion and released into circulation where it travels to the pheromone gland to activate pheromone biosynthesis. The G-protein coupled receptor that binds PBAN has been identified as well as aspects of signal transduction to activate the biosynthetic pathway. This review will highlight recent advances in the study of regulation of pheromone biosynthesis in moths.

Transcriptome analysis of Helicoverpa armigera male hairpencils: Alcohol biosynthesis and requirement for mating success

Many female animals use different strategies to assess male quality to increase their own reproductive fitness. In moths, females usually use chemical signals (sex pheromones) to attract males from a distance. Once males approach a female, they release close range pheromones from hairpencils to facilitate female acceptance. However, detailed mechanisms involved in male sex pheromone biosynthesis and its action in promoting female acceptance have not yet been fully characterized. This study screened a series of candidate genes via a transcriptome analysis of the male hairpencil of Helicoverpa armigera. Using pharmacological inhibitor and RNAi-mediated knockdown assays, we demonstrated that Ca²⁺ and cyclic-AMP were involved in pheromone biosynthesis activating neuropeptide (PBAN)-induced male sex pheromone biosynthesis. The functional analysis of candidate enzymes involved in the male sex pheromone biosynthesis pathway demonstrated that a decreased mRNA levels of acetyl-CoA carboxylase, Δ11-desaturase, and fatty-acyl reductase 2 by RNAi-mediated knockdown led to a significant decrease in the production of fatty acyl alcohols and the efficacy of female acceptance. Our results demonstrated the important role of the fatty acyl alcohol biosynthetic pathway in a PBAN-induced male sex pheromone biosynthesis and the importance of hairpencil compounds in female mating acceptance.

The mothematics of female pheromone signaling: strategies for aging virgins

Although females rarely experience strong mate limitation, delays or lifelong problems of mate acquisition are detrimental to female fitness. In systems where males search for females via pheromone plumes, it is often difficult to assess whether female signaling is costly. Direct costs include the energetics of pheromone production and attention from unwanted eavesdroppers, such as parasites, parasitoids, and predators. Suboptimal outcomes are also possible from too many or too few mating events or near-simultaneous arrival of males who make unwanted mating attempts (even if successfully thwarted). We show that, in theory, even small costs can lead to a scenario where young females signal less intensely (lower pheromone concentration and/or shorter time spent signaling) and increase signaling effort only as they age and gather evidence (while still virgin) on whether sperm limitation threatens their reproductive success. Our synthesis of the empirical data available on Lepidoptera supports this prediction for one frequently reported component of signaling-time spent calling (often reported as the time of onset of calling at night)-but not for another, pheromone titer. This difference is explicable under the plausible but currently untested assumption that signaling earlier than other females each night is a more reliable way of increasing the probability of acquiring at least one mate than producing a more concentrated pheromone plume.

Circadian rhythms and endocrine functions in adult insects

Many behavioral and physiological processes in adult insects are influenced by both the endocrine and circadian systems, suggesting that these two key physiological systems interact. We reviewed the literature and found that experiments explicitly testing these interactions in adult insects have only been conducted for a few species. There is a shortage of measurements of hormone titers throughout the day under constant conditions even for the juvenile hormones (JHs) and ecdysteroids, the best studied insect hormones. Nevertheless, the available measurements of hormone titers coupled with indirect evidence for circadian modulation of hormone biosynthesis rate, and the expression of genes encoding proteins involved in hormone biosynthesis, binding or degradation are consistent with the hypothesis that the circulating levels of many insect hormones are influenced by the circadian system. Whole genome microarray studies suggest that the modulation of farnesol oxidase levels is important for the circadian regulation of JH biosynthesis in honey bees, mosquitoes, and fruit flies. Several studies have begun to address the functional significance of circadian oscillations in endocrine signaling. The best understood system is the circadian regulation of Pheromone Biosynthesis Activating Neuropeptide (PBAN) titers which is important for the temporal organization of sexual behavior in female moths. The evidence that the circadian and endocrine systems interact has important implications for studies of insect physiology and behavior. Additional studies on diverse species and physiological processes are needed for identifying basic principles underlying the interactions between the circadian and endocrine systems in insects.

Identification of a diacylglycerol acyltransferase 2 gene involved in pheromone biosynthesis activating neuropeptide stimulated pheromone production in Bombyx mori

Diacylglycerol acyltransferase (DGAT) catalyzes the final step in triacylglycerol biosynthesis. In the present study, a DGAT2 gene from Bombyx mori was characterized. Temporal expression profiles indicated that BmDGAT2 steadily increased from 96 h before eclosion (-96 h) to an expression peak in the pheromone glands (PGs) of new-emerged female (0 h), a key stage for sex pheromone production. Spatial expression analysis revealed that the BmDGAT2 transcript was most richly expressed in PGs. Decapitation and subsequent methoprene, a juvenile hormone (JH) analog, treatment experiments revealed that JH had no influence on the expression of BmDGAT2 transcript before emergence, but inhibited the expression of BmDGAT2 transcript when administered to newly emerged adults. Further RNAi analysis confirmed that the decrease in BmDGAT2 mRNA level caused a significant reduction in sex pheromone production. Thus, DGAT2 is a key enzyme regulating B. mori sex pheromone synthesis and release.

Functional impact of silencing the Helicoverpa armigera sex-peptide receptor on female reproductive behaviour

Female Helicoverpa armigera sex pheromone production is under the control of pheromone biosynthesis-activating neuropeptide (PBAN). After mating, females undergo suppression of sex pheromone production and enhanced oviposition as a result of the transfer of male-derived seminal peptides. In a previous study we identified a putative H. armigera sex-peptide receptor (HeaSP-R) and demonstrated a significant up-regulation in gene expression levels of this receptor in brains and pheromone glands of mated females, thereby implicating a regulatory role for sex peptide in the reproductive behaviour of H. armigera. In the present study, we show that virgin females injected with Drosophila melanogaster SP (DrmSP), in addition to inhibition of pheromone production, also exhibited a suppression of calling behaviour and a significant reduction in the gene expression levels of the PBAN-receptor. In addition, RNA interference (RNAi) silencing of the HeaSP-R expression by 50-60% prevented DrmSP-suppression of pheromone production and calling behaviour. Moreover, mated, silenced females failed to increase their oviposition rates as is normally observed in mated females, and their behaviour did not differ from that of virgin females. However, sex pheromone production by mated, silenced females remained low, comparable to mated, normal females, thereby indicating the probable involvement of additional factors in the suppression of sex pheromone production after mating.

Regulatory Role of PBAN in Sex Pheromone Biosynthesis of Heliothine Moths

Both males and females of heliothine moths utilize sex-pheromones during the mating process. Females produce and release a sex pheromone for the long-range attraction of males for mating. Production of sex pheromone in females is controlled by the peptide hormone (pheromone biosynthesis activating neuropeptide, PBAN). This review will highlight what is known about the role PBAN plays in controlling pheromone production in female moths. Male moths produce compounds associated with a hairpencil structure associated with the aedaegus that are used as short-range aphrodisiacs during the mating process. We will discuss the role that PBAN plays in regulating male production of hairpencil pheromones.

Identification and differential expression of a sex-peptide receptor in Helicoverpa armigera

Sex-pheromone production in the night flying female moth, Helicoverpa armigera is under neuroendocrine control due to the timely release of Pheromone Biosynthesis-Activating Neuropeptide (PBAN). Males orient to the females by upwind anemotaxis which usually leads to a successful mating. During copulation insect males transfer seminal peptides, produced in Male Accessory Glands (MAGs) which are implicated in post-mating behavioral changes of the females. These changes include the termination of pheromone biosynthesis and thus females do not re-mate. In previous studies we showed that synthetic Drosophila melanogaster Sex-Peptide (DrmSP), which is responsible for terminating receptivity in female flies, can terminate PBAN-stimulated pheromone production by pheromone glands of the female moth, H. armigera. In addition, we demonstrated that at least one fraction of the H. armigera MAG extract is both immunoreactive to DrmSP antibody and is pheromonostatic, we also showed that different sets of DrmSP-like immunoreactive peptides are up-regulated in the central nervous system of mated females. In the present study, we identify a putative receptor for sex-peptide (SP-R) in H. armigera on the basis of sequence homologies deposited in the GenBank. In addition, in an attempt to draw some light on the physiological significance of SP-like peptides in this moth, we conducted a differential expression study of this receptor comparing gene expression levels in relation to different photoperiods, sex and mating status of the moth. Photoperiod and mating influence SP-R gene expression levels and sexual dimorphic changes were observed in neural tissues due to the different physiological states. After mating SP-R transcript levels in female neural tissues and pheromone glands are up-regulated. Physiological studies in vivo confirm the up-regulation of gene expression levels in pheromone glands isolated from mated females.

JH biosynthesis by reproductive tissues and corpora allata in adult longhorned beetles, Apriona germari

We report on juvenile hormone (JH) biosynthesis from long-chain intermediates by specific reproductive tissues and the corpora allata (CA) prepared from adult longhorned beetles, Apriona germari. The testes, male accessory glands (MAGs), ovaries, and CA contained the long-chain intermediates in the JH biosynthetic pathway, farnesoic acid (FA), methyl farnesoate (MF), and JH III. The testes and ovaries, but not CA, produced radioactive JH III after the addition of (3)H-methionine and, separately, unlabeled methionine, to the incubation medium. We inferred that endogenous FA is methylated to MF in the testes and ovaries. Addition of farnesol led to increased amounts of FA in the testes, MAGs, ovaries, and CA, indicating oxidation of farnesol to FA. Addition of FA to incubation medium yielded increased JH III, again indicating methylation of FA to MF in the testes, MAGs, ovaries, but not CA. Addition of MF to incubation medium also led to JH III, from which we inferred the epoxidation of MF to JH III. JH biosynthesis from farnesol in the testes, MAGs, and ovaries of A. germari proceeds via oxidation to FA, methylation to MF, and epoxidation to JH III. This is a well-known pathway to JH III, described here for the first time in reproductive tissues of longhorned beetles. © 2010 Wiley Periodicals, Inc.

Feeding and hemolymph trehalose concentration influence sex pheromone production in virgin Heliothis virescens moths

Previously, we demonstrated that sex pheromone production in mated female Heliothis virescens moths is dependent upon hemolymph trehalose concentration (HTC), which is influenced by activities such as the feeding of adults on sucrose. In this paper we demonstrate, for the first time, that this effect also occurs in starved (i.e., sugar-stressed) virgin females. Females allowed to feed on sugar for 6 days, following eclosion, had significantly greater titers than females that had fed only on water (i.e., were starved). No differences in pheromone titer were observed between sugar- and water-fed females at shorter (1 or 3 days) periods following eclosion. The relatively short-term effects of HTC on sex pheromone titer of virgins, were demonstrated by feeding experiments, in which starved (for 4 days) virgins fed on 10% sucrose solution had significantly greater HTC and pheromone titers than ones fed only on water; an increase in HTC was apparent within an hour, while the increase in pheromone titer was apparent within 2.5h, of sugar feeding. Starvation also showed similar effects on titers of pheromone gland fatty acids (pheromone intermediates) and HTC. Over 6 days of starvation, fatty acid titers and HTC declined gradually. After feeding on sucrose, titers of hexadecanoic, (Z)-9-hexadecanoic, (Z)-11-hexadecanoic and (Z)-9-octadecanoic, acids, as well as HTC, increased significantly 24h later, but titers of octadecanoic and (Z,Z)-9,12-octadecanoic (linoleic) acids did not. Lepidoptera cannot biosynthesize polyunsaturated acids, but the lack of change in octadecanoic acid titer suggests this acid may not participate in pheromone biosynthesis. In addition to these short-term changes in pheromone and fatty acid production, mediated by HTC, a longer-term effect of age, regardless of HTC, on pheromone titer was observed. Overall, these results are consistent with hemolymph trehalose and glandular fatty acids acting as twin metabolite reservoirs for pheromone biosynthesis. Hemolymph trehalose, able to be refilled through feeding on exogenous sugars, has a one-way flow of metabolites for synthesis of glandular free fatty acids (FFAs) and pheromone, while glandular glycerolipids provide a reversible reservoir for metabolites, accepting surplus FFAs when glandular concentrations are high, and providing FFAs for pheromone biosynthesis when concentrations are low.

Gene-silencing reveals the functional significance of pheromone biosynthesis activating neuropeptide receptor (PBAN-R) in a male moth

The role of pheromone biosynthesis activating neuropeptide (PBAN) in the regulation of pheromone biosynthesis of several female moth species is well elucidated, but its role in the males has been a mystery for over two decades since its discovery from both male and female central nervous systems. In previous studies we have identified the presence of the gene transcript for the PBAN-G-protein coupled receptor (PBAN-R) in Helicoverpa armigera male hair-pencil-aedaegus complexes (male complexes), a tissue structurally homologous to the female pheromone gland. Moreover, we showed that this transcript is up-regulated during pupal-adult development, analogous to its regulation in the female pheromone-glands, thereby indicating a likely functional gene. Here we argue in favor of PBAN's role in regulating the free fatty-acid components (myristic, palmitic, stearic, and oleic acids) and alcohol components (hexadecanol, cis-11 hexadecanol, and octadecanol) in male complexes. We demonstrate the diel periodicity in levels of male components, with peak titers occurring during the 7th-9th h in the scotophase, coincident with female pheromone production. In addition, we show significant stimulation of component levels by synthetic HezPBAN. Furthermore, we confirm PBAN's function in this tissue through knockdown of the PBAN-R gene using RNAi-mediated gene-silencing. Injections of PBAN-R dsRNA into the male hemocoel significantly inhibited levels of the various male components by 58%-74%. In conclusion, through gain and loss of function we revealed the functionality of the PBAN-R and the key components that are up-regulated by PBAN.