Role of the Halloween genes, Spook and Phantom in ecdysteroidogenesis in the desert locust, Schistocerca gregaria

Halloween genes are expressed with a circadian rhythm during development in prothoracic glands of the insect RHODNIUS PROLIXUS

We analyse the developmental and circadian profiles of expression of the genes responsible for ecdysteroidogenesis (Halloween genes) in the PGs of Rhodnius prolixus throughout larval-adult development. Extensive use of in vitro techniques enabled multiple different parameters to be measured in individual PGs. Expression of disembodied and spook closely paralleled the ecdysteroid synthesis of the same PGs, and the ecdysteroid titre in vivo, but with functionally significant exceptions. Various tissues other than PGs expressed one, both or neither genes. Both gonads express both genes in pharate adults (larvae close to ecdysis). Both genes were expressed at low, but significant, levels in UF Rhodnius, raising questions concerning how developmental arrest is maintained in UF animals. IHC confirmed the subcellular localisation of the coded proteins. Gene knockdown suppressed transcription of both genes and ecdysteroid synthesis, with spook apparently regulating the downstream gene disembodied. Transcription of both genes occurred with a daily rhythm (with peaks at night) that was confirmed to be under circadian control using aperiodic conditions. The complex behaviour of the rhythm in LL implied two anatomically distinct oscillators regulate this transcription rhythm. First, the circadian clock in the PGs and second, the circadian rhythm of of Rhodnius PTTH which is released rhythmically from the brain under control of the circadian clock therein, both of which were described previously. We conclude ecdysteroidogenesis in Rhodnius PGs employs a similar pathway as other insects, but its control is complex, involving mechanisms both within and outside the PGs.

RNAi-mediated silencing of the neverland gene inhibits molting in the migratory locust, Locusta migratoria

7-dehydrocholesterol (7-DHC) is a key intermediate product used for biosynthesis of molting hormone. This is achieved through a series of hydroxylation reactions catalyzed by the Halloween family of cytochrome P450s. Neverland is an enzyme catalyzes the first reaction of the ecdysteroidogenic pathway, which converts dietary cholesterol into 7-DHC. However, research on the physiological function of neverland in orthopteran insects is lacking. In this study, neverland from Locusta migratoria (LmNvd) was cloned and analyzed. LmNvd was mainly expressed in the prothoracic gland and highly expressed on days 6 and 7 of fifth instar nymphs. RNAi-mediated silencing of LmNvd resulted in serious molting delays and abnormal phenotypes, which could be rescued by 7-DHC and 20-hydroxyecdysone supplementation. Hematoxylin and eosin staining results showed that RNAi-mediated silencing of LmNvd disturbed the molting process by both promoting the synthesis of new cuticle and suppressing the degradation of the old cuticle. Quantitative real-time PCR results suggested that the mRNA expression of E75 early gene and chitinase 5 gene decreased and that of chitin synthase 1 gene was markedly upregulated after knockdown of LmNvd. Our results suggest that LmNvd participates in the biosynthesis process of molting hormone, which is involved in regulating chitin synthesis and degradation in molting cycles.

Dual function of the transcription factor Ftz-f1 on oviposition in the cockroach Blattella germanica

The transcription factor Ftz-f1 has multiple functions in insect development in a spatial-temporal line. One of these roles is in the insect ovaries, specifically in the regulation of steroidogenic enzymes production. We studied the function of F in Blattella germanica oogenesis, as it shows two moments of high expression in ovaries: before the imaginal moult, and just before ovulation in the adult. Injecting dsftz-f1 into adult females, either just after the imaginal moult or just prior to choriogenesis, prevented oviposition, with differences between the two approaches. In 3-day-old adult females treated with dsftz-f1 just after the emergence, the expression of ftz-f1 was not modified, but the steroidogenic genes increased their expression. ftz-f1 transcript levels in the ovaries of 5-day-old dsftz-f1-treated females were significantly depleted, and the expression levels of the same steroidogenic genes began to decrease. These results suggest that Ftz-f1 regulates the expression of steroidogenic genes in B. germanica, with phm possibly being a key target. Ftz-f1 has a different temporal function in the cytoskeleton of follicular cells of the basal ovarian follicles. Early in the gonadotrophic cycle, Ftz-f1 promotes the expression of genes related to the cytoskeleton and muscle proteins, while at the end of the cycle it maintains the expression levels of these genes, thus ensuring correct ovulation.

Sublethal and transgenerational effects of lufenuron on biological characteristics and expression of reproductive related genes in the fall armyworm, Spodoptera frugiperda

The fall armyworm, Spodoptera frugiperda, is a notorious polyphagous pest that causes serious economic losses in crucial crops and has invaded Africa and Asia. Lufenuron is widely used for controlling S. frugiperda in China, owing to its high toxicity against this key pest, and less pollution and little impact on natural enemies. In the present study, the sublethal and transgenerational effects of lufenuron on S. frugiperda were investigated to provide in-depth information for the rational use of lufenuron. Results showed that the development time and pupae weight were not significantly affected following exposure of females to LC10 and LC25 and male S. frugiperda to the LC10 of lufenuron. However, LC25 exposure significantly reduced pupal and total development time and pupae weight of male S. frugiperda. The longevity of S. frugiperda adults was prolonged by lufenuron and the fecundity of S. frugiperda treated with LC10 of lufenuron was significantly increased by 40% compared to the control. In addition, our study demonstrated that the LC25 of lufenuron had transgenerational effects on the progeny generation. The development time of female S. frugiperda whose parents were exposed to LC25 of lufenuron was significantly decreased compared to the control. And then, the expression profiles of Vg, VgR, JHEH, JHE, JHAMT, JHBP, CYP307A1, CYP306A1, CYP302A1 and CYP314A1 genes involved in insect reproduction and development were analyzed using Quantitative Real-Time PCR (RT-qPCR). Results showed that Vg, VgR, JHE, JHAMT, and CYP306A1 were significantly upregulated at the LC10 of lufenuron, which revealed that these upregulated genes might be linked with increased fecundity of S. frugiperda. Taken together, these findings highlighted the importance of sublethal and transgenerational effects under laboratory conditions and these effects may change the population dynamics in the field. Therefore, our study provided valuable information for promoting the rational use of lufenuron for controlling S. frugiperda.

Ecdysteroid Biosynthesis Halloween Gene Spook Plays an Important Role in the Oviposition Process of Spider Mite, Tetranychus urticae

In insects, the ecdysteroid hormone regulates development and reproduction. However, its function in the reproduction process of spider mites is still unclear. In this study, we investigated the effect of the Halloween gene Spook on the oviposition of the reproduction process in a spider mite, Tetranychus urticae. The expression patterns of the ecdysteroid biosynthesis and signaling pathway genes, as analyzed by RT-qPCR, showed that the expression pattern of the Halloween genes was similar to the oviposition pattern of the female mite and the expression patterns of the vitellogenesis-related genes TuVg and TuVgR, suggesting that the Halloween genes are involved in the oviposition of spider mites. To investigate the function of the ecdysteroid hormone on the oviposition of the reproduction process, we carried out an RNAi assay against the Halloween gene Spook by injection in female mites. Effective silencing of TuSpo led to a significant reduction of oviposition. In summary, these results provide an initial study on the effect of Halloween genes on the reproduction in T. urticae and may be a foundation for a new strategy to control spider mites.

Exorista sorbillans (Diptera: Tachinidae) parasitism shortens host larvae growth duration by regulating ecdysone and juvenile hormone titers in Bombyx mori (Lepidoptera: Bombycidae)

The tachinid fly, Exorista sorbillans, is a notorious ovolarviparous endoparasitoid of the silkworm, Bombyx mori, causing severe damage to silkworm cocoon industry. Silkworm larvae show typically precocious wandering behavior after being parasitized by E. sorbillans; however, the underlying molecular mechanism remains unexplored. Herein, we investigated the changes in the levels of 20-hydroxyecdysone (20E) and juvenile hormone (JH) titer, and they both increased in the hemolymph of parasitized silkworms. Furthermore, we verified the expression patterns of related genes, which showed an upregulation of 20E signaling and biosynthesis genes but a significant downregulation of ecdysone oxidase (EO), a 20E inactivation enzyme, in parasitized silkworms. In addition, related genes of the JH signaling were activated in parasitized silkworms, while related genes of the JH degradation pathway were suppressed, resulting in an increase in JH titer. Notably, the precocious wandering behavior of parasitized silkworms was partly recoverable by silencing the transcriptions of BmCYP302A1 or BmCYP307A1 genes. Our findings suggest that the developmental duration of silkworm post parasitism could be shortened by regulation of 20E and JH titers, which may help silkworm to resist the E. sorbillans infestation. These findings provide a basis for deeper insight into the interplay between silkworms and E. sorbillans and may serve as a reference for the development of a novel approach to control silkworm myiasis.

The loss of Halloween gene function seriously affects the development and reproduction of Diaphorina citri (Hemiptera: Liviidae) and increases its susceptibility to pesticides

The citrus industry has suffered severe losses as a result of Huanglongbing spread by Diaphorina citri. Controlling the population of D. citri is the key to preventing and controlling the spread of Huanglongbing. Ecdysteroids are key hormones that regulate insect development and reproduction. Therefore, the Halloween gene family involved in the ecdysone synthesis of D. citri is an ideal target for controlling the population growth of this insect. In this study, we successfully cloned four Halloween genes expressed during D. citri development. Silencing of one of the four genes resulted in a significant decrease in 20E titers in nymphs and significant decreases in the developmental, survival and emergence rates. Inhibiting Halloween gene expression in adults impeded the growth of the female ovary, diminished yolk formation, lowered vitellogenin transcription levels, and hence impaired female fecundity. This showed that Halloween genes were required for D. citri development and reproduction. DcCYP315A1 and DcCYP314A1 were highly expressed when D. citri was exposed to thiamethoxam and cypermethrin, and silencing these two genes made D. citri more sensitive to these two pesticides. Inhibition of DcCYP315A1 and DcCYP314A1 expression not only significantly delayed the development and reproduction of D. citri but also increased its susceptibility to pesticides. Therefore, these two genes are more suitable as potential target genes for controlling D. citri.

Ammonia Stress Disturbs Moult Signaling in Juvenile Swimming Crab Portunus trituberculatus

Ammonia is a significant concern during hatchery culture in brachyuran species, and its accumulation may lead to abortive moulting and large-scale deaths of the early juveniles. To date, the underlying mechanism for ammonia-induced alteration of the moulting process is still unknown. In this study, we aimed to investigate the effects of ammonia on the moulting as well as the potential mechanisms in early juveniles of the swimming crab Portunus trituberculatus, an important aquaculture species in China. We evaluated the survival rate and moulting rate of the juvenile crabs (C2) and analyzed the expression pattern of the genes in key components of molt signaling during a complete moulting cycle under different concentrations of ammonia nitrogen (the control group: <0.1 mg/L; the LA group: 5 mg/L; and the HA group: 20 mg/L). The results showed that: (1) the survival rate in the LA and HA groups was lower than that in the control group at the end of the experiment, and moulting death syndrome (MDS) was only observed in the HA group; (2) the moulting rate was higher in the LA group and lower in the HA group compared to the control group; (3) consistent with the results of the moulting experiment, MIH showed decreased expression, and genes related to ecdysteroid synthesis, ecdysteroid receptors, and responsive effectors exhibited increased expression in the LA group compared to the control group; and (4) although MIH expression was upregulated, increased expression of the genes associated with ecdysteroid synthesis, ecdysteroid receptors and downstream effectors still observed in the HA group. Our results indicated that low levels of ammonia can promote moulting in juvenile swimming crabs by inhibiting the expression of MIH and activating moult signaling, whereas high levels of ammonia inhibit moulting and lead to MDS through impairing moult signaling.

Genome-Wide Identification and Expression Pattern of Cytochrome P450 Genes in the Social Aphid Pseudoregma bambucicola

Cytochrome P450 monooxygenases (P450s) have a variety of functions, including involvement in the metabolism of exogenous substances and the synthesis and degradation of endogenous substances, which are important for the growth and development of insects. Pseudoregma bambucicola is a social aphid that produces genetically identical but morphologically and behaviorally distinct first-instar soldiers and normal nymphs within colonies. In this study, we identified 43 P450 genes based on P. bambucicola genome data. Phylogenetic analysis showed that these genes were classified into 4 clans, 13 families, and 23 subfamilies. The CYP3 and CYP4 clans had a somewhat decreased number of genes. In addition, differential gene expression analysis based on transcriptome data showed that several P450 genes, including CYP18A1, CYP4G332, and CYP4G333, showed higher expression levels in soldiers compared to normal nymphs and adult aphids. These genes may be candidates for causing epidermal hardening and developmental arrest in soldiers. This study provides valuable data and lays the foundation for the study of functions of P450 genes in the social aphid P. bambucicola.

Identification and characterization of CYP307A1 as a molecular target for controlling the small hive beetle, Aethina tumida

BACKGROUND

The molting hormone 20-hydroxyecdysone (20E) plays a key role in insect development, metamorphosis, and reproduction. Previous studies have shown that ecdysteroid metabolism is regulated by a series of CYP genes in most of the insect species. However, the roles of these CYP genes in a Coleopteran beetle, Aethina tumida (small hive beetle, SHB) have not yet been explored.

RESULTS

In the current study, we identified seven CYP genes (six Halloween genes and one AtCYP18A1 gene) related to 20E metabolism. Reverse transcription quantitative polymerase chain reaction (RT-qPCR) showed that AtCYP307A1 and AtCYP307B1 were primarily expressed in the embryonic stage and in the cephalothorax of larvae. RNA interference (RNAi) screening revealed that suppression of AtCYP307A1 expression caused a lethal phenotype during the larval-pupal metamorphosis. Furthermore, Hematoxylin and Eosin staining of the integument showed that the RNAi of AtCYP307A1 inhibited the apolysis and degradation of the old cuticle. In addition, silencing of AtCYP307A1 resulted in significant down-regulation of 20E titers and the expression levels of 20E signaling pathway genes. Finally, the AtCYP307A1 RNAi phenotype was rescued by topical application of 20E.

CONCLUSION

Our studies suggest that AtCYP307A1 involved in 20E synthesis is indispensable during the larval-pupal metamorphosis of beetles, which could serve as a putative insecticide target for pest control. © 2022 Society of Chemical Industry.

Knockdown of the Halloween Genes spook, shadow and shade Influences Oocyte Development, Egg Shape, Oviposition and Hatching in the Desert Locust

Ecdysteroids are widely investigated for their role during the molting cascade in insects; however, they are also involved in the development of the female reproductive system. Ecdysteroids are synthesized from cholesterol, which is further converted via a series of enzymatic steps into the main molting hormone, 20-hydoxyecdysone. Most of these biosynthetic conversion steps involve the activity of cytochrome P450 (CYP) hydroxylases, which are encoded by the Halloween genes. Three of these genes, spook (spo), phantom (phm) and shade (shd), were previously characterized in the desert locust, Schistocerca gregaria. Based on recent sequencing data, we have now identified the sequences of disembodied (dib) and shadow (sad), for which we also analyzed spatiotemporal expression profiles using qRT-PCR. Furthermore, we investigated the possible role(s) of five different Halloween genes in the oogenesis process by means of RNA interference mediated knockdown experiments. Our results showed that depleting the expression of SchgrSpo, SchgrSad and SchgrShd had a significant impact on oocyte development, oviposition and hatching of the eggs. Moreover, the shape of the growing oocytes, as well as the deposited eggs, was very drastically altered by the experimental treatments. Consequently, it can be proposed that these three enzymes play an important role in oogenesis.

RNAi-Mediated Silencing of Putative Halloween Gene Phantom Affects the Performance of Rice Striped Stem Borer, Chilo suppressalis

The physiological and biochemical characterization of the "Halloween" genes has fundamental importance in the biosynthesis pathway of ecdysteroids. These genes were found to catalyze the final phases of ecdysteroid biosynthesis from dietary cholesterol to the molting hormone 20-hydroxyecdysone. We report the characterization of the Cs-Phm in a major insect pest in agriculture, the rice striped stem borer, Chilo suppressalis (C. suppressalis). A full-length transcript of Cs-Phm was amplified with an open reading frame (ORF) of 478 amino acids through 5' and 3' RACE. Cs-Phm shows five insect-conserved P450 motifs: Helix-C, Helix-I, Helix-K, PERF, and heme-binding motifs. Phylogenetic analysis clearly shows high similarity to Lepidoptera and evolutionary conservation in insects. The relative spatial and temporal transcript profile shows that Cs-Phm is highly expressed in the prothoracic glands and appears throughout the larval development, but with low expression at the start of the larval instar. It seems to peak in 3-4 days and decreases again before the larvae molt. Double-stranded RNA (dsRNA) injection of Cs-Phm at the larval stage efficiently knocked down the target gene and decreased its expression level. The dsRNA-treated group showed significantly decreased ecdysteroid titers, which leads to delayed larval development and higher larval mortality. Negative effects of larval development were rescued by treating 20E in the dsRNA-treated group. Thus, in conclusion, our results suggest that Cs-Phm is functionally conserved in C. suppressalis and encodes functional CYP that contributes to the biogenesis of 20E.

Sublethal doses of broflanilide prevents molting in the fall armyworm, Spodoptera frugiperda via altering molting hormone biosynthesis

Broflanilide is a novel insecticide with a unique mode of action on the insect GABA receptor and is registered worldwide for the control of agricultural pests. It shows high efficacy in controlling the fall armyworm (FAW) Spodoptera frugiperda, which is a destructive pest to various crops. FAW was exposed to sublethal concentrations of broflanilide to determine its impact on insect development. Sublethal doses (LD₁₀ and LD₃₀) caused failure of ecdysis, reduced body length of larvae, malformation of pupae, and vestigial wing formation in adults. Also, broflanilide at LD₃₀ significantly reduced the amount of molting hormone (MH). After exposure to LD₁₀ or LD₃₀ broflanilide, expression of five Halloween genes, which participate in MH biosynthesis, were found to be altered. Specifically, the transcript levels of SfrCYP307A1 (Spook), SfrCYP314A1 (Shade) and SfrCYP315A1 (Shadow) in 3rd day larvae were significantly decreased as well as SfrCYP302A1 (Disembodied) and SfrCYP306A1 (Phantom) in 5th day pupae. In contrast, the transcript levels of SfrCYP302A1 in 3rd day larvae, SfrCYP307A1 and SfrCYP314A1 in 5th day pupae, and SfrCYP306A1, SfrCYP307A1 and SfrCYP315A1 in 0.5th day adults were significantly increased. Our results demonstrate that broflanilide caused the failure of ecdysis in FAW possibly by influencing the intake of cholesterol through inhibition of feeding and also via altering expression of genes important for MH biosynthesis.

Characteristics of Halloween genes and RNA interference-mediated functional analysis of LmCYP307a2 in Locusta migratoria

Halloween genes are involved in the biosynthesis of the molting hormone, which plays a key role in insect ecdysis, development, metamorphosis, and reproduction. Our previous work identified five Halloween genes from Locusta migratoria, but their functions are currently unknown. In this study, the sequences of these five Halloween genes were analyzed and characterized. LmCYP307a2, LmCYP306a1, LmCYP302a1, and LmCYP315a1 were primarily expressed in the prothoracic glands, while LmCYP314a1 was universally expressed in peripheral tissues, especially in the ovaries and Malpighian tubules. All five Halloween genes were mainly expressed from the 5th to the 7th d in 5th-instar nymphs. RNA interference (RNAi) silencing of LmCYP307a2 resulted in severe molting delays and molting failure, which could be rescued by supplementary 20-hydroxyecdysone. A hematoxylin and eosin staining analysis suggested that the RNAi of LmCYP307a2 inhibited the ecdysis process by inhibiting the apolysis and degradation of the old cuticle, and by promoting the synthesis of a new cuticle. Quantitative reverse transcription polymerase chain reaction results showed that the expressions of LmE74, LmCht5, and LmCht10 were dramatically down-regulated, while that of LmChsI was substantially up-regulated, after knockdown of LmCYP307a2. The results suggest that LmCYP307a2 is related to the molt process via regulation of chitin synthesis and degradation.

Prothoracicostatic Activity of the Ecdysis-Regulating Neuropeptide Crustacean Cardioactive Peptide (CCAP) in the Desert Locust

Accurate control of innate behaviors associated with developmental transitions requires functional integration of hormonal and neural signals. Insect molting is regulated by a set of neuropeptides, which trigger periodic pulses in ecdysteroid hormone titers and coordinate shedding of the old cuticle during ecdysis. In the current study, we demonstrate that crustacean cardioactive peptide (CCAP), a structurally conserved neuropeptide described to induce the ecdysis motor program, also exhibits a previously unknown prothoracicostatic activity to regulate ecdysteroid production in the desert locust, Schistocerca gregaria. We identified the locust genes encoding the CCAP precursor and three G protein-coupled receptors that are activated by CCAP with EC₅₀ values in the (sub)nanomolar range. Spatiotemporal expression profiles of the receptors revealed expression in the prothoracic glands, the endocrine organs where ecdysteroidogenesis occurs. RNAi-mediated knockdown of CCAP precursor or receptors resulted in significantly elevated transcript levels of several Halloween genes, which encode ecdysteroid biosynthesis enzymes, and in elevated ecdysteroid levels one day prior to ecdysis. Moreover, prothoracic gland explants exhibited decreased secretion of ecdysteroids in the presence of CCAP. Our results unequivocally identify CCAP as the first prothoracicostatic peptide discovered in a hemimetabolan species and reveal the existence of an intricate interplay between CCAP signaling and ecdysteroidogenesis.

RNA interference shows that Spook, the precursor gene of 20-hydroxyecdysone (20E), regulates the molting of Macrobrachium nipponense

The aim of this study was to explore the function of the Mn-Spook gene, which was found in the ovary transcriptome of the Oriental river prawn (Macrobrachium nipponense). The Spook gene, which is the precursor gene of 20-hydroxyecdysone (20E), plays an important role in the process of molting in many arthropods, but its function in M. nipponense is unclear. We cloned the full-length Mn-Spook gene from the ovary of M. nipponense and found that it had the same conserved domains as the P450 gene of the Halloween family of genes. The Mn-Spook gene was highly expressed in ovary and gill tissue during the breeding period. During ovarian development, Mn-spook gene expression was highest at the nearly-ripe stage, and it also was highly expressed in the zoea developmental stage. Cellular localization analysis showed that Mn-Spook signals accumulated in the cytoplasmic membrane and nucleus of oocytes. Finally, we used RNA interference to evaluate the function of the Mn-Spook gene. Compared with the control group, in vivo injection of Mn-Spook dsRNA effectively downregulated the expression of Mn-Spook and the content of 20E. The molting frequency of M. nipponense in the experimental group also was significantly inhibited. These results demonstrated that the Mn-Spook gene played an important role in the molting process of M. nipponense.

Understanding molt control switches: Transcriptomic and expression analysis of the genes involved in ecdysteroidogenesis and cholesterol uptake pathways in the Y-organ of the blue crab, Callinectes sapidus

The crustacean molting process is regulated by an interplay of hormones produced by the eyestalk ganglia and Y-organs (YO). Molt-inhibiting hormone and crustacean hyperglycemic hormone released by the sinus gland of the eyestalk ganglia (EG) inhibit the synthesis and secretion of ecdysteroid by the YO, hence regulating hemolymph levels during the molt cycle. The purpose of this study is to investigate the ecdysteroidogenesis pathway, specifically genes linked to changes in ecdysteroid levels occurring at early premolt (ePM). To this end, a reference transcriptome based on YO, EG, and hepatopancreas was de novo assembled. Two genes (cholesterol 7-desaturase Neverland and cytochrome p450 307a1-like Spook) involved in ecdysteroidogenesis were identified from the YO transcriptome using sequence comparisons and transcript abundance. Two other candidates, Hormone receptor 4 and probable cytochrome p450 49a1 potentially involved in ecdysteroidogenesis were also identified. Since cholesterol is the ecdysteroid precursor, a putative cholesterol carrier (Apolipoprotein D-like) was also examined to understand if cholesterol uptake coincided with the increase in the ecdysteroid levels at the ePM stage. The expression level changes of the five candidate genes in the YO were compared between intermolt (IM) and induced ePM (iePM) stages using transcriptomic analysis. Expression analysis using qPCR were carried out at IM, iePM, and normal ePM. The increase in Spook and Neverland expression in the YO at the ePM was accompanied by a concomitant rise in ecdysteroid levels. The data obtained from iePM stage were congruent with those obtained from the normal ePM stage of intact control animals. The present findings support the role of Halloween genes in the ecdysteroidogenesis and molt cycle in the blue crab, Callinectes sapidus.

Role of Endocrine System in the Regulation of Female Insect Reproduction

The proper synthesis and functioning of ecdysteroids and juvenile hormones (JHs) are very important for the regulation of vitellogenesis and oogenesis. However, their role and function contrast among different orders, and even in the same insect order. For example, the JH is the main hormone that regulates vitellogenesis in hemimetabolous insect orders, which include Orthoptera, Blattodea, and Hemiptera, while ecdysteroids regulate the vitellogenesis among the insect orders of Diptera, some Hymenoptera and Lepidoptera. These endocrine hormones also regulate each other. Even at some specific stage of insect life, they positively regulate each other, while at other stages of insect life, they negatively control each other. Such positive and negative interaction of 20-hydroxyecdysone (20E) and JH is also discussed in this review article to better understand the role of these hormones in regulating the reproduction. Therefore, the purpose of the present review is to deeply understand the complex interaction of endocrine hormones with each other and with the insulin signaling pathway. The role of microbiomes in the regulation of the insect endocrine system is also reviewed, as the endocrine hormones are significantly affected by the compounds produced by the microbiota.

RNAi-Mediated Knockdown of Transcription Factor E93 in Nymphs of the Desert Locust (Schistocerca gregaria) Inhibits Adult Morphogenesis and Results in Supernumerary Juvenile Stages

Postembryonic development of insects is coordinated by juvenile hormone (JH) together with ecdysteroids. Whereas the JH early response gene krüppel-homolog 1 (Kr-h1) plays a crucial role in the maintenance of juvenile characteristics during consecutive larval stages, the ecdysteroid-inducible early gene E93 appears to be a key factor promoting metamorphosis and adult morphogenesis. Here, we report on the developmental and molecular consequences of an RNAi-mediated knockdown of SgE93 in the desert locust, Schistocerca gregaria, a hemimetabolan species. Our experimental data show that injection of gregarious locust nymphs with a double-stranded RNA construct targeting the SgE93 transcript inhibited the process of metamorphosis and instead led to supernumerary nymphal stages. These supernumerary nymphal instars still displayed juvenile morphological features, such as a nymphal color scheme and body shape, while they reached the physical body size of the adult locusts, or even surpassed it after the next supernumerary molt. Interestingly, when compared to control locusts, the total duration of the fifth and normally final nymphal (N5) stage was shorter than normal. This appeared to correspond with temporal and quantitative changes in hemolymph ecdysteroid levels, as well as with altered expression of the rate-limiting Halloween gene, Spook (SgSpo). In addition, the levels of the ecdysone receptor (SgEcR) and retinoïd X receptor (SgRXR) transcripts were altered, indicating that silencing SgE93 affects both ecdysteroid synthesis and signaling. Upon knockdown of SgE93, a very potent upregulation of the SgKr-h1 transcript levels was observed in both head and fat body, while no significant changes were detected in the transcript levels of SgJHAMT and SgCYP15A1, the enzymes that catalyze the two final steps in JH biosynthesis. Moreover, the process of molting was disturbed in these supernumerary nymphs. While attempting ecdysis to the next stage, 50% of the N6 and all N7 nymphal instars eventually died. S. gregaria is a very harmful, swarm-forming pest species that destroys crops and threatens food security in many of the world's poorest countries. We believe that a better knowledge of the mechanisms of postembryonic development may contribute to the discovery of novel, more selective and sustainable strategies for controlling gregarious locust populations. In this context, identification of molecular target candidates that are capable of significantly reducing the fitness of this devastating swarming pest will be of crucial importance.

Functional analysis of ecdysteroid biosynthetic enzymes of the rice planthopper, Nilaparvata lugens

Ecdysteroids, insect steroid hormones, play key roles in regulating insect development and reproduction. Hemipteran insects require ecdysteroids for egg production; however, ecdysteroid synthesis (ecdysteroidogenesis) details have not been elucidated. We identified all known genes encoding ecdysteroidogenic enzymes in Nilaparvata lugens and clarified their necessity during nymphal and ovarian development. We confirmed that N. lugens utilized 20-hydroxyecdysone as an active hormone. Assays using heterologous expression of enzymes in Drosophila S2 cells showed conserved functions of enzymes Neverland, CYP306A2, CYP314A1 and CYP315A1, but not CYP302A1. RNA interference and rescue analysis using 20-hydroxyecdysone demonstrated that most of the genes were necessary for nymphal development. The identified N. lugens enzymes showed conserved functions and pathways for ecdysteroidogenesis. Knockdown of ecdysteroidogenic enzyme genes in newly molted females caused failure of egg production: less vitellogenic and mature eggs in ovaries, fewer laid eggs and embryonic development deficiency of laid eggs. Considering the high expressions of ecdysteroidogenic enzyme genes in adults and ovaries, ecdysteroidogenesis in ovaries was critical for N. lugens ovarian development. Our study presents initial evidence that hemipteran insects require ecdysteroidogenesis for ovarian development.

Molecular characterization and functional analysis of the Halloween genes and CYP18A1 in Bemisia tabaci MED

The ecdysteroid hormone 20-hydroxyecdysone (20E), a critical hormone in arthropods, plays an essential role in insect growth, molting and reproduction. A previous study showed that 20E is actually regulated by six P450 genes (five P450 genes belonging to the Halloween family and a CYP18A1 gene) in model insects. However, the role of the six P450 genes in Bemisia tabaci Q (also call Mediterranean, MED), an important pest of field crops, remains unclear. Here, six P450 genes were cloned by RT-PCR, and the phylogenetic tree indicated a close orthologous relationship of these P450 genes between MED and other insects. Spatiotemporal expression profiling revealed that five P450 genes (CYP18A1, CYP306A1, CYP307A2, CYP314A1 and CYP315A1) were expressed at significantly higher levels in the head than in the abdomen and thorax. Four P450 genes (CYP302A1, CYP307A2, CYP314A1 and CYP315A1) were expressed at the highest levels in males, and CYP18A1 was expressed at the highest levels in the 4th nymph stage. The molting process was delayed by approximately 1-3 days after knockdown of these genes at the 4th nymph stage, and the mean proportion of shriveled or dead insects reached 8.3% (CYP18A1), 20.8% (CYP302A1), 7.0% (CYP307A2), 31.8% (CYP306A1), 28.6% (CYP314A1) and 24.1% (CYP315A1). In addition, 20E rescued the negative effect of ds-CYP306A1, ds-CYP314A1 and ds-CYP315A1 on the eclosion rate. We concluded that these Halloween genes and CYP18A1 likely participate in the development of MED, and in particular, CYP306A1 could be used as a putative insecticide target for controlling this piercing-sucking insect.

Pheromone biosynthetic pathway and chemoreception proteins in sex pheromone gland of Eogystia hippophaecolus

The moth Eogystia hippophaecolus (Hua et al.) is a major threat to sea buckthorn plantations in China. Specific and highly efficient artificial sex pheromone traps have been developed and used to control this pest species. However, the biosynthesis of sex pheromones Z7-14: Ac and E3-14:Ac remains poorly understood. We investigated the female pheromone gland transcriptome of E. hippophaecolus and identified two pheromone biosynthesis-activating neuropeptides (PBANs), two pheromone biosynthesis-activating neuropeptide receptors (PBANrs), five acetyl-CoA carboxylases (ACCs), six fatty acid synthases (FASs), 16 Acyl-CoA desaturases (DESs), 26 reductases (REDs), 13 acetyltransferases (ACTs), one fatty acid transport protein (FATP), one acyl-CoA-binding protein (ACBP), and five elongation of very long-chain fatty acid proteins (ELOs) in pheromone biosynthesis pathways. Additionally, we identified 11 odorant-degrading enzymes (ODEs) and 16 odorant-binding proteins (OBPs), 14 chemosensory proteins (CSPs), two sensory neuron membrane proteins (SNMPs), three odorant receptors (ORs), seven ionotropic receptors (IRs), and six gustatory receptors (GRs). 77 unigenes involved in female pheromone biosynthesis, 31 chemoreception proteins and 11 odorant degradation enzymes were identified, which provided insight into the regulation of the pheromone components and pheromone recognition in the sex pheromone gland, and knowledge pertinent to new integrated pest management strategy of interference pheromone biosynthesis and recognition.

A new neuropeptide insect parathyroid hormone iPTH in the red flour beetle Tribolium castaneum

In the postgenomics era, comparative genomics have advanced the understanding of evolutionary processes of neuropeptidergic signaling systems. The evolutionary origin of many neuropeptidergic signaling systems can be traced date back to early metazoan evolution based on the conserved sequences. Insect parathyroid hormone receptor (iPTHR) was previously described as an ortholog of vertebrate PTHR that has a well-known function in controlling bone remodeling. However, there was no sequence homologous to PTH sequence in insect genomes, leaving the iPTHR as an orphan receptor. Here, we identified the authentic ligand insect PTH (iPTH) for the iPTHR. The taxonomic distribution of iPTHR, which is lacking in Diptera and Lepidoptera, provided a lead for identifying the authentic ligand. We found that a previously described orphan ligand known as PXXXamide (where X is any amino acid) described in the cuttlefish Sepia officinalis has a similar taxonomic distribution pattern as iPTHR. Tests of this peptide, iPTH, in functional reporter assays confirmed the interaction of the ligand-receptor pair. Study of a model beetle, Tribolium castaneum, was used to investigate the function of the iPTH signaling system by RNA interference followed by RNA sequencing and phenotyping. The results suggested that the iPTH system is likely involved in the regulation of cuticle formation that culminates with a phenotype of defects in wing exoskeleton maturation at the time of adult eclosion. Moreover, RNAi of iPTHRs also led to significant reductions in egg numbers and hatching rates after parental RNAi.

Vertebrate parathyroid hormone (PTH) and its receptors have been extensively studied with respect to their function in bone remodeling and calcium metabolism. Insect parathyroid hormone receptors (iPTHRs) have been previously described as counterparts of vertebrate PTHRs, however, they are still orphan receptors for which the authentic ligands and biological functions remain unknown. We describe an insect form of parathyroid hormone (iPTH) by analyzing its interactions with iPTHRs. Identification of this new insect peptidergic system proved that the PTH system is an ancestral signaling system dating back to the evolutionary time before the divergence of protostomes and deuterostomes. We also investigated the functions of the iPTH system in a model beetle Tribolium castaneum by using RNA interference. RNA interference of iPTHR resulted in defects in wing exoskeleton maturation and fecundity. Based on the differential gene expression patterns and the phenotype induced by RNAi, we propose that the iPTH system is likely involved in the regulation of exoskeletal cuticle formation and fecundity in insects.

Transcriptome of pleuropodia from locust embryos supports that these organs produce enzymes enabling the larva to hatch

Background

Pleuropodia are limb-derived glandular organs that transiently appear on the first abdominal segment in embryos of insects from majority of “orders”. They are missing in the genetic model Drosophila and little is known about them. Experiments carried out on orthopteran insects 80 years ago indicated that the pleuropodia secrete a “hatching enzyme” that digests the serosal cuticle to enable the larva to hatch, but evidence by state-of-the-art molecular methods is missing.

Results

We used high-throughput RNA-sequencing to identify the genes expressed in the pleuropodia of the locust Schistocerca gregaria (Orthoptera). First, using transmission electron microscopy we studied the development of the pleuropodia during 11 stages of the locust embryogenesis. We show that the glandular cells differentiate and start secreting just before the definitive dorsal closure of the embryo and the secretion granules outside the cells become more abundant prior to hatching. Next, we generated a comprehensive embryonic reference transcriptome for the locust and used it to study genome wide gene expression across ten morphologicaly defined stages of the pleuropodia. We show that when the pleuropodia have morphological markers of functional organs and produce secretion, they are primarily enriched in transcripts associated with transport functions. They express genes encoding enzymes capable of digesting cuticular protein and chitin. These include the potent cuticulo-lytic Chitinase 5, whose transcript rises just before hatching. Unexpected finding was the enrichment in transcripts for immunity-related enzymes. This indicates that the pleuropodia are equipped with epithelial immunity similarly as barrier epithelia in postembryonic stages.

Conclusions

These data provide transcriptomic support for the historic hypothesis that pleuropodia produce cuticle-degrading enzymes and function in hatching. They may also have other functions, such as facilitation of embryonic immune defense. By the genes that they express the pleuropodia are specialized embryonic organs and apparently an important though neglected part of insect physiology.

Sublethal effects of chlorantraniliprole on molting hormone levels and mRNA expressions of three Halloween genes in the rice stem borer, Chilo suppressalis

While sublethal effects of insecticide on insect development have been widely studied, the underlying mechanisms remain elusive. Our previous studies revealed that sublethal concentrations of chlorantraniliprole significantly increased the juvenile hormone levels and resulted in both prolonged developmental time and reduced fecundity in Chilo suppressalis. In the present study, we evaluated the sublethal effects of chlorantraniliprole on molting hormone (MH) levels and mRNA expressions of three Halloween genes including CsCYP307A1, CsCYP306A1 and CsCYP314A1 in C. suppressalis. The results showed that the MH levels in different developmental stages of C. suppressalis were decreased after exposure to LC₁₀ and LC₃₀ of chlorantraniliprole. However, analysis of temporal expression profiles revealed that the mRNA levels of three Halloween genes were not closely correlated with the ecdysteroid titers in C. suppressalis. Notably, the transcript levels of CsCYP307A1, CsCYP306A1 and CsCYP314A1 were induced after treatment with sublethal concentrations of chlorantraniliprole in specific developmental stages. These results indicated that chlorantraniliprole had adverse effects on insect MH biosynthesis, and in addition to the involvement in MH biosynthesis, CsCYP307A1, CsCYP306A1 and CsCYP314A1 may also play important roles in the detoxification metabolism of chlorantraniliprole in C. suppressalis.

Identification of Halloween Genes and RNA Interference-Mediated Functional Characterization of a Halloween Gene shadow in Plutella xylostella

Ecdysteroids play an essential role in controlling insect development and reproduction. Their pathway is regulated by a group of enzymes called Halloween gene proteins. The relationship between the Halloween genes and ecdysteroid synthesis has yet to be clearly understood in diamondback moth, Plutella xylostella (L.), a worldwide Lepidoptera pest attacking cruciferous crops and wild plants. In this study, complete sequences for six Halloween genes, neverland (nvd), shroud (sro), spook (spo), phantom (phm), disembodied (dib), shadow (sad), and shade (shd), were identified. Phylogenetic analysis revealed a strong conservation in insects, including Halloween genes of P. xylostella that was clustered with all other Lepidoptera species. Three Halloween genes, dib, sad, and shd were highly expressed in the adult stage, while nvd and spo were highly expressed in the egg and pupal stages, respectively. Five Halloween genes were highly expressed specifically in the prothorax, which is the major site of ecdysone production. However, shd was expressed predominantly in the fat body to convert ecdysone into 20-hydroxyecdysone. RNAi-based knockdown of sad, which is involved in the last step of ecdysone biosynthesis, significantly reduced the 20E titer and resulted in a longer developmental duration and lower pupation of fourth-instar larvae, as well as caused shorter ovarioles and fewer fully developed eggs of P. xylostella. Furthermore, after the knockdown of sad, the expression levels of Vg and VgR genes were significantly decreased by 77.1 and 53.0%. Meanwhile, the number of eggs laid after 3 days was significantly reduced in sad knockdown females. These results suggest that Halloween genes may play a critical role in the biosynthesis of ecdysteroids and be involved in the development and reproduction of P. xylostella. Our work provides a solid basis for understanding the functional importance of these genes, which will help to screening potential genes for pest management of P. xylostella.

Juvenile Hormone receptor Met is essential for ovarian maturation in the Desert Locust, Schistocerca gregaria

Juvenile hormones (JH) are key endocrine regulators produced by the corpora allata (CA) of insects. Together with ecdysteroids, as well as nutritional cues, JH coordinates different aspects of insect postembryonic development and reproduction. The function of the recently characterized JH receptor, Methoprene-tolerant (Met), appears to be conserved in different processes regulated by JH. However, its functional interactions with other hormonal signalling pathways seem highly dependent on the feeding habits and on the developmental and reproductive strategies employed by the insect species investigated. Here we report on the effects of RNA interference (RNAi) mediated SgMet knockdown during the first gonadotrophic cycle in female desert locusts (Schistocerca gregaria). This voracious, phytophagous pest species can form migrating swarms that devastate field crops and harvests in several of the world’s poorest countries. A better knowledge of the JH signalling pathway may contribute to the development of novel, more target-specific insecticides to combat this very harmful swarming pest. Using RNAi, we show that the JH receptor Met is essential for ovarian maturation, vitellogenesis and associated ecdysteroid biosynthesis in adult female S. gregaria. Interestingly, knockdown of SgMet also resulted in a significant decrease of insulin-related peptide (SgIRP) and increase of neuroparsin (SgNP) 3 and 4 transcript levels in the fat body, illustrating the existence of an intricate regulatory interplay between different hormonal factors. In addition, SgMet knockdown in females resulted in delayed display of copulation behaviour with virgin males, when compared with dsGFP injected control animals. Moreover, we observed an incapacity of adult dsSgMet injected female locusts to oviposit during the time of the experimental setup. As such, SgMet is an essential gene playing crucial roles in the endocrine communication necessary for successful reproduction of the desert locust.

RNA Interference in Insects: Protecting Beneficials and Controlling Pests

Insects constitute the largest and most diverse group of animals on Earth with an equally diverse virome. The main antiviral immune system of these animals is the post-transcriptional gene-silencing mechanism known as RNA(i) interference. Furthermore, this process can be artificially triggered via delivery of gene-specific double-stranded RNA molecules, leading to specific endogenous gene silencing. This is called RNAi technology and has important applications in several fields. In this paper, we review RNAi mechanisms in insects as well as the potential of RNAi technology to contribute to species-specific insecticidal strategies. Regarding this aspect, we cover the range of strategies considered and investigated so far, as well as their limitations and the most promising approaches to overcome them. Additionally, we discuss patterns of viral infection, specifically persistent and acute insect viral infections. In the latter case, we focus on infections affecting economically relevant species. Within this scope, we review the use of insect-specific viruses as bio-insecticides. Last, we discuss RNAi-based strategies to protect beneficial insects from harmful viral infections and their potential practical application. As a whole, this manuscript stresses the impact of insect viruses and RNAi technology in human life, highlighting clear lines of investigation within an exciting and promising field of research.

The ecdysone receptor complex is essential for the reproductive success in the female desert locust, Schistocerca gregaria

Ecdysteroid hormones influence the development and reproduction of arthropods by binding a heterodimeric complex of nuclear receptors, the ecdysone receptor (EcR) and the retinoid-X-receptor/ultraspiracle (RXR/USP). Here, we report on the in vivo role(s) of the ecdysone receptor complex, SchgrEcR/SchgrRXR, in the female reproductive physiology of a major phytophagous pest insect, i.e. the desert locust, Schistocerca gregaria. Tissue and temporal distribution profiles were analysed during the first gonadotrophic cycle of adult female locusts. RNA interference was used as a reverse genetics tool to investigate the in vivo role of the ecdysone receptor complex in ovarian maturation, oogenesis, fertility and fecundity. We discovered that silencing the ecdysone receptor complex in S. gregaria resulted in impaired ovulation and oviposition, indicative for a crucial role of this complex in chorion formation. We also found evidence for a feedback of SchgrEcR/SchgrRXR on juvenile hormone biosynthesis by the corpora allata. Furthermore, we observed a tissue-dependent effect of the SchgrEcR/SchgrRXR knockdown on the transcript levels of the insulin receptor and neuroparsin 3 and 4. The insulin receptor transcript levels were upregulated in the brain, but not the fat body and gonads. Neuroparsins 3 and 4 transcript levels were down regulated in the brain and fat body, but not in the gonads.

Sensilla on six olfactory organs of male Eogystia hippophaecolus (Lepidoptera: Cossidae)

Eogystia hippophaecolus (Hua et al.) is an important boring pest that primarily damages sea buckthorn, causing large ecological and economic damages in China. In this study, we used scanning electron microscopy to investigate the sensilla on six olfactory tissues of male E. hippophaecolus: antennae, labial palps, external genitals, propodeum, mesopodium, and metapedes. On the antennae, two types of sensillum trichodea, two types of sensillum basiconica, a type of sensillum coeloconica, and Böhm's bristles were found. The labial palps had sensilla trichodea and chaetica. On the external genitals, three types of sensilla trichodea were the only sensilla. Böhm bristles were found on the base of the tibia and at the terminus of the tarsus. Most sensilla were distributed on the tarsus of the three pairs of legs, and notably, a majority of which were sensilla trichodea and sensilla chaetica, were on the pretarsus and telotarsus of the three pairs of legs. In this study, the distribution, number, type, and morphology of the sensilla on six olfactory organs of E. hippophaecolus were determined, which established the foundation for a future immunohistochemical search of olfactory proteins. RESEARCH HIGHLIGHTS: Eogystia hippophaecolus is a serious pest of seabuckthorn. The distribution, number, type, and morphology of olfactory sensilla of E. hippophaecolus are determined. The function and distribution of sensilla are compared with those of other insects.

Pheromone Binding Protein EhipPBP1 Is Highly Enriched in the Male Antennae of the Seabuckthorn Carpenterworm and Is Binding to Sex Pheromone Components

The seabuckthorn carpenterworm moth Eogystia hippophaecolus is a major threat to seabuckthorn plantations, causing considerable ecological and economic losses in China. Transcriptomic analysis of E. hippophaecolus previously identified 137 olfactory proteins, including three pheromone-binding proteins (PBPs). We investigated the function of E. hippophaecolus PBP1 by studying its mRNA and protein expression profiles and its binding ability with different compounds. The highest levels of expression were in the antennae, particularly in males, with much lower levels of expression in the legs and external genitals. Recombinant PBP1 showed strong binding to sex-pheromone components, suggesting that antennal EhipPBP1 is involved in binding sex-pheromone components during pheromone communication.

Role of the venus kinase receptor in the female reproductive physiology of the desert locust, Schistocerca gregaria

Venus kinase receptors (VKR) are a subfamily of invertebrate receptor tyrosine kinases, which have only recently been discovered. They contain an intracellular tyrosine kinase domain and an extracellular Venus FlyTrap domain. VKRs have been functionally and pharmacologically characterized in only two invertebrate species, namely the human parasite Schistosoma mansoni and the mosquito Aedes aegypti, where they play a crucial role in oogenesis. Here, we report the characterization of a VKR in the desert locust, Schistocerca gregaria. We performed an in-depth profiling study of the SgVKR transcript levels in different tissues throughout the female adult stage. Using the RNA interference technique, the possible role of SgVKR was investigated. SgVKR knockdown had significant effects on ovarian ecdysteroid levels and on the size of oocytes during the vitellogenic stage. SgVKR is probably involved in the complex cross-talk between several important pathways regulating female reproductive physiology. Contrary to A. aegypti and S. mansoni, we cannot conclude that this receptor is essential for reproduction, since silencing SgVKR did not affect fecundity or fertility. Considering the evolutionary distance between A. aegypti and S. gregaria, as well as the differences in regulation of their female reproductive physiology, this article constitutes a valuable asset in better understanding VKRs.

The ecdysis triggering hormone system is essential for successful moulting of a major hemimetabolous pest insect, Schistocerca gregaria

Insects are enclosed in a rigid exoskeleton, providing protection from desiccation and mechanical injury. To allow growth, this armour needs to be replaced regularly in a process called moulting. Moulting entails the production of a new exoskeleton and shedding of the old one and is induced by a pulse in ecdysteroids, which activates a peptide-mediated signalling cascade. In Holometabola, ecdysis triggering hormone (ETH) is the key factor in this cascade. Very little functional information is available in Hemimetabola, which display a different kind of development characterized by gradual changes. This paper reports on the identification of the ETH precursor and the pharmacological and functional characterisation of the ETH receptor in a hemimetabolous pest species, the desert locust, Schistocerca gregaria. Activation of SchgrETHR by SchgrETH results in an increase of both Ca²⁺ and cyclic AMP, suggesting that SchgrETHR displays dual coupling properties in an in vitro cell-based assay. Using qRT-PCR, an in-depth profiling study of SchgrETH and SchgrETHR transcripts was performed. Silencing of SchgrETH and SchgrETHR resulted in lethality at the expected time of ecdysis, thereby showing their crucial role in moulting.

RNA interference-mediated knockdown of the Halloween gene Spookiest (CYP307B1) impedes adult eclosion in the western tarnished plant bug, Lygus hesperus

Ecdysteroids play a critical role in coordinating insect growth, development and reproduction. A suite of cytochrome P450 monooxygenases coded by what are collectively termed Halloween genes mediate ecdysteroid biosynthesis. In this study, we describe cloning and RNA interference (RNAi)-mediated knockdown of the CYP307B1 Halloween gene (Spookiest) in the western tarnished plant bug, Lygus hesperus. Transcripts for Ly. hesperus Spookiest (LhSpot) were amplified from all life stages and correlated well with timing of the pre-moult ecdysteroid pulse. In adults, LhSpot was amplified from heads of both genders as well as female reproductive tissues. Heterologous expression of a LhSpot fluorescent chimera in cultured insect cells co-localized with a fluorescent marker of the endoplasmic reticulum/secretory pathway. RNAi-mediated knockdown of LhSpot in fifth instars reduced expression of ecdysone-responsive genes E74 and E75, and prevented adult development. This developmental defect was rescued following application of exogenous 20-hydroxyecdysone but not exogenous 7-dehydrocholesterol. The unequivocal RNAi effects on Ly. hesperus development and the phenotypic rescue by 20-hydroxyecdysone are causal proof of the involvement of LhSpot in ecdysteroid biosynthesis and related developmental processes, and may provide an avenue for development of new control measures against Ly. hesperus.

Antennal transcriptome analysis and expression profiles of odorant binding proteins in Eogystia hippophaecolus (Lepidoptera: Cossidae)

Background

Eogystia hippophaecolus (Hua et al.) (Lepidoptera: Cossidae) is the major threat to seabuckthorn plantations in China. Specific and highly efficient artificial sex pheromone traps was developed and used to control it. However, the molecular basis for the pheromone recognition is not known. So we established the antennal transcriptome of E. hippophaecolus and characterized the expression profiles of odorant binding proteins. These results establish and improve the basis knowledge of the olfactory receptive system, furthermore provide a theoretical basis for the development of new pest control method.

Results

We identified 29 transcripts encoding putative odorant-binding proteins (OBPs), 18 putative chemosensory proteins (CSPs), 63 odorant receptors (ORs), 13 gustatory receptors (GRs), 12 ionotropic receptors (IRs), and two sensory neuron membrane proteins (SNMPs). Based on phylogenetic analysis, we found one Orco and three pheromone receptors of E. hippophaecolus and found that EhipGR13 detects sugar, EhipGR11 and EhipGR3 detect bitter. Nine OBPs expression profile indicated that most were the highest expression in antennae, consistent with functions of OBPs in binding and transporting odors during the antennal recognition process. OBP6 was external expressed in male genital-biased in, and this locus may be responsible for pheromone binding and recognition as well as mating. OBP1 was the highest and biased expressed in the foot and may function as identification of host plant volatiles.

Conclusions

One hundred thirty-seven chemosensory proteins were identified and the accurate functions and groups of part proteins were obtained by phylogenetic analysis. The most OBPs were antenna-biased expressed, which are involved in antennal recognition. However, few OBP was detected biased expression in the foot and external genitalia, and these loci may function in pheromone recognition, mating, and the recognition of plant volatiles.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-016-3008-4) contains supplementary material, which is available to authorized users.

Ecdysteroid signalling components in metamorphosis and development of the desert locust, Schistocerca gregaria

The arthropod-specific hormone family of ecdysteroids plays an important role in regulating diverse physiological processes, such as moulting and metamorphosis, reproduction, diapause and innate immunity. Ecdysteroids mediate their response by binding to a heterodimeric complex of two nuclear receptors, the ecdysone receptor (EcR) and the retinoid-X-receptor/ultraspiracle (RXR/USP). In this study we investigated the role of EcR and RXR in metamorphosis and development of the desert locust, Schistocerca gregaria. The desert locust is a voracious, phytophagous, swarming pest that can ruin crops and harvests in some of the world's poorest countries. A profound knowledge of the ecdysteroid signalling pathway can be used in the development of more target-specific insecticides to combat this harmful plague insect. Here we report an in-depth profiling study of the transcript levels of EcR and RXR, as well as its downstream response genes, in different tissues isolated throughout the last larval stage of a hemimetabolous insect, showing a clear correlation with circulating ecdysteroid titres. Using RNA interference (RNAi), the role of SgEcR/SgRXR in moulting and development was investigated. We have proven the importance of the receptor components for successful moulting of locust nymphs into the adult stage. Some SgEcR/SgRXR knockdown females were arrested in the last larval stage, and 65 % of them initiated vitellogenesis and oocyte maturation, which normally only occurs in adults. Furthermore, our results clearly indicate that at the peak of ecdysteroid synthesis, on day six of the last larval stage, knockdown of SgEcR/SgRXR is affecting the transcript levels of the Halloween genes, Spook, Shadow and Shade.

The effect of silencing 20E biosynthesis relative genes by feeding bacterially expressed dsRNA on the larval development of Chilo suppressalis

RNA interference (RNAi) is a robust tool to study gene functions as well as potential for insect pest control. Finding suitable target genes is the key step in the development of an efficient RNAi-mediated pest control technique. Based on the transcriptome of Chilo suppressalis, 24 unigenes which putatively associated with insect hormone biosynthesis were identified. Amongst these, four genes involved in ecdysteroidogenesis i.e., ptth, torso, spook and nm-g were evaluated as candidate targets for function study. The partial cDNA of these four genes were cloned and their bacterially expressed dsRNA were fed to the insects. Results revealed a significant reduction in mRNA abundance of target genes after 3 days. Furthermore, knocked down of these four genes resulted in abnormal phenotypes and high larval mortality. After 15 days, the survival rates of insects in dsspook, dsptth, dstorso, and dsnm-g groups were significantly reduced by 32%, 38%, 56%, and 67% respectively, compared with control. Moreover, about 80% of surviving larvae showed retarded development in dsRNA-treated groups. These results suggest that oral ingestion of bacterially expressed dsRNA in C. suppressalis could silence ptth, torso, spook and nm-g. Oral delivery of bacterially expressed dsRNA provides a simple and potential management scheme against C. suppressalis.

Role of Halloween genes in ecdysteroids biosynthesis of the swimming crab (Portunus trituberculatus): Implications from RNA interference and eyestalk ablation

Molting, including metamorphosis molting in arthropods are controlled by the ecdysteroids that are synthesized and secreted by the crustacean Y-organ (YO) or the insect prothoracic gland (PG). The Halloween genes encoding the enzymes mainly involved in the biosynthesis of ecdysteroids are well studied in insects but not in crustaceans. Given the importance of Halloween genes in ecdysteroids biosynthesis, we have previously reported the cDNA cloning of disembodied (Dib) in P. trituberculatus. Here, cDNA sequences of another two Halloween genes, Spook (Spo) and Shadow (Sad), were further identified and characterized. The predicted amino acid sequences for these two Halloween genes of Portunus trituberculatus were compared to those of several other arthropods, and several typical domains of the cytochrome P450 mono-oxygenase (CYP) were identified. Similar to the tissue distribution of Dib, the Spo and Sad also showed high specificity to the YO. RNA interference (RNAi) of these 3 genes indicated they all play essential role in ecdysteroids biosynthesis. To investigate the relationships of the Halloween genes to the eyestalk neuropeptides such as molt-inhibiting hormone (MIH), effects of eyestalk ablation (ESA) on the expression of Dib, Spo and Sad were detected. Expression of Dib and Sad, but not Spo, was significantly induced by ESA. The result indicated that the inhibition of MIH in ecdysteroids biosynthesis may be partly through the transcriptional regulation of certain Halloween genes, such as Dib and Sad, while the Spo might not be the target for MIH signal.

Knockdown of juvenile hormone acid methyl transferase severely affects the performance of Leptinotarsa decemlineata (Say) larvae and adults

BACKGROUND

Juvenile hormone (JH) plays a critical role in the regulation of metamorphosis in Leptinotarsa decemlineata, a notorious defoliator of potato. JH acid methyltransferase (JHAMT) is involved in one of the final steps of JH biosynthesis.

RESULTS

A putative JHAMT cDNA (LdJHAMT) was cloned. Two double-stranded RNAs (dsRNAs) (dsJHAMT1 and dsJHAMT2) against LdJHAMT were constructed and bacterially expressed. Experiments were conducted to investigate the effectiveness of RNAi in both second- and fourth-instar larvae. Dietary introduction of dsJHAMT1 and dsJHAMT2 successfully knocked down the target gene, lowered JH titre in the haemolymph and reduced the transcript of Krüppel homologue 1 gene. Ingestion of dsJHAMT caused larval death and weight loss, shortened larval developmental period and impaired pupation. Moreover, the dsJHAMT-fed pupae exhibited lower adult emergence rates. The resulting adults weighed an average of 50 mg less than the control group, and the females did not deposit eggs. Application of pyriproxyfen to the dsJHAMT-fed insects rescued all the negative effects.

CONCLUSIONS

LdJHAMT expresses functional JHAMT enzyme. The RNAi targeting LdJHAMT could be used for control of L. decemlineata. © 2015 Society of Chemical Industry.

Molecular cloning and characterization of the putative Halloween gene Phantom from the small brown planthopper Laodelphax striatellus

Ecdysteroid hormone 20-hydroxyecdysone plays fundamental roles in insect postembryonic development and reproduction. Several cytochrome P450 mono-oxygenases (CYPs), encoded by the Halloween genes, have been documented to be involved in ecdysteroidogenesis in representative insects in Diptera, Lepidoptera and Orthoptera. Here the putative Halloween gene Phantom (Phm, cyp306a1) from a hemipteran insect species, the small brown planthopper Laodelphax striatellus, was cloned. LsPHM shows five insect conserved P450 motifs, that is, Helix-C, Helix-I, Helix-K, PERF and heme-binding motifs. Temporal and spatial expression patterns of LsPhm were evaluated by quantitative polymerase chain reaction. Through the fourth-instar and the early fifth-instar stages, LsPhm showed two expression peaks in day 2 and days 4-5 fourth-instar nymphs, and three troughs in day 1 and 3 fourth instars and day 1 fifth instars. On day 5 of the fourth-instar nymphs, LsPhm clearly had a high transcript level in the thorax where the prothoracic glands were located. Dietary introduction of double-stranded RNA (dsRNA) of LsPhm at the nymph stage successfully knocked down the target gene, decreased expression level of ecdysone receptor (LsEcR) gene and caused a higher nymphal mortality rate and delayed development. Ingestion of 20-hydroxyecdysone on LsPhm-dsRNA-exposed nymphs did not increase LsPhm expression level, but almost completely rescued the LsEcR mRNA level, and relieved the negative effects on survival and development. Thus, our data suggest that the putative LsPhm encodes a functional 25-hydroxylase that catalyzes the biosynthesis of ecdysteroids in L. striatellus.

RXR/USP and EcR are critical for the regulation of reproduction and the control of JH biosynthesis in Diploptera punctata

During development and reproduction the response to ecdysteroids is mediated by a heterodimeric receptor complex comprising the retinoid X receptor/ultraspiracle (RXR/USP) and the ecdysone receptor (EcR). Here, the role of these receptors in the endocrine control of reproduction is examined in the cockroach Diploptera punctata. We report the sequence of four DpRXR and three DpEcR splice variants, including the first description of a Drosophila EcRB2-like isoform in a hemimetabolous insect. DpRXR and DpEcR are broadly expressed in the tissues of adult females, with relatively high transcript levels in the corpora allata (CA), nervous tissue and ovary. Developmental profiling revealed an inverse correlation between DpRXR and DpEcR expression and the activity of the CA. RNAi-mediated depletion of DpRXR and DpEcR did not affect oocyte growth, but inhibited oviposition and impaired chorion formation. Retained oocytes exhibited a degenerating follicular epithelium and were slowly resorbed. Treated animals showed significantly higher rates of JH biosynthesis and a decrease in ecdysteroid titers at the end of vitellogenesis. Reduction of DpRXR and DpEcR expression resulted in an upregulation of genes involved in JH production and a downregulation of allatostatin receptor mRNA in the CA. Treatment with dsRNA also affected the expression of genes downstream of JH in target tissues including vitellogenin and Krüppel-homolog 1 as well as Broad-Complex, an early ecdysone response gene. Overall, results suggest that DpRXR and DpEcR are not required early in the reproductive cycle when events are JH-dependent, but do mediate critical ecdysteroid feedback to the CA late in the gonadotropic cycle.

Three Halloween genes from the Varroa mite, Varroa destructor (Anderson & Trueman) and their expression during reproduction

The ecdysteroid biosynthetic pathway involves sequential enzymatic hydroxylations by a group of enzymes collectively known as Halloween gene proteins. Complete sequences for three Halloween genes, spook (Vdspo), disembodied (Vddib) and shade (Vdshd), were identified in varroa mites and sequenced. Phylogenetic analyses of predicted amino acid sequences for Halloween orthologues showed that the acarine orthologues were distantly associated with insect and crustacean clades indicating that acarine genes had more ancestral characters. The lack of orthologues or pseudogenes for remaining genes suggests these pathway elements had not evolved in ancestral arthropods. Vdspo transcript levels were highest in gut tissues, while Vddib transcript levels were highest in ovary-lyrate organs. In contrast, Vdshd transcript levels were lower overall but present in both gut and ovary-lyrate organs. All three transcripts were present in eggs removed from gravid female mites. A brood cell invasion assay was developed for acquiring synchronously staged mites. Mites within 4 h of entering a brood cell had transcript levels of all three that were not significantly different from mites on adult bees. These analyses suggest that varroa mites may be capable of modifying 7-dehydro-cholesterol precursor and hydroxylations of other steroid precursors, but whether the mites directly produce ecdysteroid precursors and products remains undetermined.

The silkworm glutathione S-transferase gene noppera-bo is required for ecdysteroid biosynthesis and larval development

Insect molting and metamorphosis are tightly controlled by ecdysteroids, which are important steroid hormones that are synthesized from dietary sterols in the prothoracic gland. One of the ecdysteroidogenic genes in the fruit fly Drosophila melanogaster is noppera-bo (nobo), also known as GSTe14, which encodes a member of the epsilon class of glutathione S-transferases. In D. melanogaster, nobo plays a crucial role in utilizing cholesterol via regulating its transport and/or metabolism in the prothoracic gland. However, it is still not known whether the orthologs of nobo from other insects are also involved in ecdysteroid biosynthesis via cholesterol transport and/or metabolism in the prothoracic gland. Here we report genetic evidence showing that the silkworm Bombyx mori ortholog of nobo (nobo-Bm; GSTe7) is essential for silkworm development. nobo-Bm is predominantly expressed in the prothoracic gland. To assess the functional importance of nobo-Bm, we generated a B. mori genetic mutant of nobo-Bm using TALEN-mediated genome editing. We show that loss of nobo-Bm function causes larval arrest and a glossy cuticle phenotype, which are rescued by the application of 20-hydroxyecdysone. Moreover, the prothoracic gland cells isolated from the nobo-Bm mutant exhibit an abnormal accumulation of 7-dehydrocholesterol, a cholesterol metabolite. These results suggest that the nobo family of glutathione S-transferases is essential for development and for the regulation of sterol utilization in the prothoracic gland in not only the Diptera but also the Lepidoptera. On the other hand, loss of nobo function mutants of D. melanogaster and B. mori abnormally accumulates different sterols, implying that the sterol utilization in the PG is somewhat different between these two insect species.

Initiation of metamorphosis and control of ecdysteroid biosynthesis in insects: The interplay of absence of Juvenile hormone, PTTH, and Ca(2+)-homeostasis

The paradigm saying that release of the brain neuropeptide big prothoracicotropic hormone (PTTH) initiates metamorphosis by activating the Torso-receptor/ERK pathway in larval prothoracic glands (PGs) is widely accepted nowadays. Upon ligand-receptor interaction Ca(2+) enters the PG cells and acts as a secondary messenger. Ecdysteroidogenesis results, later followed by apoptosis. Yet, some data do not fit in this model. In some species decapitated animals can still molt, even repeatedly, and metamorphose. PTTH does not universally occur in all insect species. PGs may also have other functions; PGs as counterpart of the vertebrate thymus? There are also small PTTHs. Finally, PTTH remains abundantly present in adults and plays a role in control of ecdysteroidogenesis (=sex steroid production) in gonads. This is currently documented only in males. This urges a rethinking of the PTTH-PG paradigm. The key question is: Why does PTTH-induced Ca(2+) entry only result in ecdysteroidogenesis and apoptosis in specific cells/tissues, namely the PGs and gonads? Indeed, numerous other neuropeptides also use Ca(2+) as secondary messenger. The recent rediscovery that in both invertebrates and vertebrates at least some isoforms of Ca(2+)-ATPase need the presence of an endogenous farnesol/juvenile hormone(JH)-like sesquiterpenoid for keeping cytosolic [Ca(2+)]i below the limit of apoptosis-induction, triggered the idea that it is not primarily PTTH, but rather the drop to zero of the JH titer that acts as the primordial initiator of metamorphosis by increasing [Ca(2+)]i. PTTH likely potentiates this effect but only in cells expressing Torso. PTTH: an evolutionarily ancient gonadotropin?

RNA interference-mediated silencing of a Halloween gene spookier affects nymph performance in the small brown planthopper Laodelphax striatellus

Post-embryonic development of insects is highly dependent on ecdysteroid hormone 20-hydroxyecdysone. Halloween gene spookier (spok, cyp307a2) has been documented to be involved in ecdysteroidogenesis in Drosophila melanogaster and Bombyx mori. We describe here the cloning and characterization of Halloween gene spookier (Lsspok, Lscyp307a2) in the small brown planthopper Laodelphax striatellus, a hemipteran insect species. LsSPOK has three insect-conserved P450 motifs, that is, Helix-K, PERF motif and heme-binding domain. Temporal and spatial expression patterns of Lsspok were evaluated by quantitative polymerase chain reaction. Through the fouth-instar and the early fifth-instar stages, Lsspok showed two expression peaks in the second- and fifth-day fourth-instar nymphs, and two troughs in the first-day fourth and fifth instars. On day 5 of the fourth-instar nymphs, Lsspok clearly had a high transcript level in the thorax where prothoracic glands were located. Dietary introduction of double-stranded RNA of Lsspok in the nymph stage successfully knocked down the target gene, decreased expression level of ecdysone receptor (LsEcR) gene, caused nymphal lethality and delayed development. Ingestion of 20-hydroxyecdysone in Lsspok-dsRNA-exposed nymphs did not increase Lsspok expression level, but almost completely rescued the LsEcR mRNA level and relieved the negative effects on survival and development. Thus, our data suggest that the ecdysteroidogenic pathway is conserved in insects and LsSPOK is responsible for specific steps in ecdysteroidogenesis in L. striatellus.

Molecular cloning and characterization of the allatotropin precursor and receptor in the desert locust, Schistocerca gregaria

Allatotropins (ATs) are pleiotropic neuropeptides initially isolated from the tobacco hornworm, Manduca sexta. In 2008, the first receptor for AT-like peptides (ATR) was characterized in Bombyx mori. Since then, ATRs have also been characterized in M. sexta, Tribolium castaneum, Aedes aegypti and Bombus terrestris. These receptors show sequence similarity to vertebrate orexin (ORX) receptors. When generating an EST-database of the desert locust (Schistocerca gregaria) central nervous system, we found cDNA sequences encoding the Schgr-AT precursor and a fragment of its putative receptor. This receptor cDNA has now been completed and functionally expressed in mammalian cell lines. Activation of this receptor, designated as Schgr-ATR, by Schgr-AT caused an increase in intracellular calcium ions, as well as cyclic AMP (cAMP), with an EC₅₀ value in the nanomolar range. In addition, the transcript distribution of both the Schgr-AT precursor and Schgr-ATR was investigated by means of quantitative real-time PCR. Moreover, we found more evidence for the myotropic and allatostimulatory actions of Schgr-AT in the desert locust. These data are discussed and situated in a broader context by comparison with literature data on AT and ATR in insects.

Knockdown of Cs-Spook induces delayed larval molting in rice striped stem borer Chilo suppressalis

Spook has essential roles in the biogenesis of the molting hormone 20-hydroxyecdysone (20-E). The function of spook in the rice striped stem borer (SSB) Chilo suppressalis remains unclear, prompting our hypothesis that it exerts actions similar to those reported for other insect species. Here we amplified the full-length transcript of spook (Cs-Spook) in SSB by 5' and 3' rapid amplification of cDNA ends. Cs-Spook has conserved P450 motifs such as Helix-C, Helix-I, Helix-K, and PERF motif (PxxFxPxRF). It was highly expressed in late instar larvae but less so in newly molted larvae. Cs-Spook was highly expressed in prothoracic glands. Cs-Spook was knocked down by dsRNA treatments. Compared with controls, the gene expression level was reduced to 9% at 24 h post injection (PI), 33% at 48 h PI, and 24% at 72 h PI. The ecdysteroid titer decreased significantly in the dsRNA-treated group (P < 0.05), resulting in delayed larval development. The delayed development in dsRNA-treatment group was rescued by treating with 20-E. Our work demonstrates that Cs-Spook participates in the biogenesis of 20-E and regulates the molt of SSB, as seen in other species.

A Halloween gene shadow is a potential target for RNA-interference-based pest management in the small brown planthopper Laodelphax striatellus

BACKGROUND

Laodelphax striatellus is an economically important rice pest in China. Ecdysteroid hormone 20-hydroxyecdysone regulates insect development and reproduction. The cytochrome P450 monooxygenase Shadow (Sad) plays a critical role in ecdysteroidogenesis. Here, tests were conducted to establish whether Lssad was a potential target gene for RNA-interference-based management of L. striatellus.

RESULTS

Lssad was cloned and characterised. LsSad had Helix-C, Helix-I, Helix-K, PERF and haem-binding motifs. Lssad is expressed at a higher level in the thorax, where prothoracic glands are located, compared with the level in the head or abdomen. It showed two expression peaks in day 2 and day 4-5 fourth-instar nymphs, and two troughs in day 1 fourth and fifth instars. Oral delivery of double-stranded RNA (dsRNA) of Lssad at the nymph stage successfully knocked down the expression of the target gene, reduced the expression level of ecdysone receptor (LsEcR) gene, caused nymphal lethality and delayed development in a dose-dependent manner. Ingestion of 20-hydroxyecdysone in Lssad-dsRNA-exposed nymphs did not increase Lssad expression level, but almost completely rescued the LsEcR mRNA level and relieved the negative effects on survival and development.

CONCLUSIONS

The ecdysteroidogenic pathway is conserved in L. striatellus. Lssad can serve as a possible target for dsRNA-based pesticides for planthopper control.