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Imidacloprid is one of the most commonly used insecticides and seriously threatens the survival of honeybees. Juvenile hormone III (JHIII), an important hormone in honeybees, plays a central role in the life cycle of honeybees; however, the mechanism by which JHIII responds to imidacloprid stress has not been determined. In this study, the resistance of Apis cerana cerana (Acc) to imidacloprid was greater than that of Apis mellifera (Am), and the application of JHIII significantly increased the resistance of both species of honeybees. RTqPCR revealed that two genes, juvenile hormone acid methyltransferase (JHAMT) and methyl farnesoate epoxidase (MFE), which are involved in JHIII biosynthesis, are key genes for improving resistance to imidacloprid via JHIII in honeybees. Silencing JHAMT and MFE with RNAi resulted in a lower content of JHIII in Acc and reduced resistance to imidacloprid. The exogenous application of JHIII compensated for the reduced resistance phenotype caused by gene silencing. Furthermore, histological examination of paraffin sections revealed that imidacloprid treatment caused loose intestinal cell arrangement, slight damage to columnar digestive cells and muscle cells, and chromatin condensation in basal layer cells. JHIII treatment reduced the degree of damage to the honeybee midgut cells and improved resistance to imidacloprid. The results of this study provide a new perspective and molecular basis for the study of the regulation of JHIII and the toxicity of imidacloprid in honeybees.

Juvenile hormone plays a “status quo” role in Drosophila melanogaster larvae, preventing the untimely metamorphosis, and performs a gonadotropic function in imagoes, ensuring the ovaries’ preparedness for vitellogenesis. The decreased level of juvenile hormone results in reproductive disorders in D. melanogaster females including a delay in the oviposition onset and a fertility decrease. Another factor that can affect the insect reproduction is an infection with the maternally inherited symbiotic α-proteobacterium Wolbachia. The present study is devoted to the analysis of the expression of two juvenile hormone metabolism genes encoding enzymes of its synthesis and degradation, juvenile hormone acid O-methyltransferase ( jhamt) and juvenile hormone epoxide hydrase (Jheh1), respectively, in four wild-type D. melanogaster lines, two of them being infected with Wolbachia. Lines w153 and Bi90 were both derived from an individual wild-caught females infected with Wolbachia, while lines w153T and Bi90T were derived from them by tetracycline treatment and are free of infection. Line Bi90 is known to be infected with the Wolbachia strain wMel, and line w153, with the Wolbachia strain wMelPlus belonging to the wMelCS genotype. It was found that infection with either Wolbachia strain does not affect the expression of the studied genes. At the same time, it was shown that the w153 and w153T lines differ from the Bi90 and Bi90T lines by an increased level of the Jheh1 gene expression and do not differ in the jhamt gene expression level. Analysis of the fertility of these four lines showed that it does not depend on Wolbachia infection either, but differs between lines with different nuclear genotypes: in w153 and w153T, it is significantly lower than in lines Bi90 and Bi90T. The data obtained allow us to reasonably propose that the inter-line D. melanogaster polymorphism in the metabolism of the juvenile hormone is determined by its degradation (not by its synthesis) and correlates with the fertility level.

Abstract Background In insects, an interplay between the activities of distinct hormones, such as juvenile hormone (JH) and 20-hydroxyecdysone (20E), regulates the progression through numerous life history hallmarks. As a crucial endocrine factor, JH is mainly synthesized in the corpora allata (CA) to regulate multiple physiological and developmental processes, including molting, metamorphosis, and reproduction. During the last century, significant progress has been achieved in elucidating the JH signal transduction pathway, while less progress has been made in dissecting the regulatory mechanism of JH biosynthesis. Previous work has shown that receptor tyrosine kinase (RTK) signaling regulates hormone biosynthesis in both insects and mammals. Here, we performed a systematic RNA interference (RNAi) screening to identify RTKs involved in regulating JH biosynthesis in the CA of adult Blattella germanica females. Results We found that the epidermal growth factor receptor (Egfr) is required for promoting JH biosynthesis in the CA of adult females. The Egf ligands Vein and Spitz activate Egfr, followed by Ras/Raf/ERK signaling, and finally activation of the downstream transcription factor Pointed (Pnt). Importantly, Pnt induces the transcriptional expression of two key enzyme-encoding genes in the JH biosynthesis pathway: juvenile hormone acid methyltransferase (JHAMT) and methyl farnesoate epoxidase (CYP15A1). Dual-luciferase reporter assay shows that Pnt is able to activate a promoter region of Jhamt. In addition, electrophoretic mobility shift assay confirms that Pnt directly binds to the − 941~ − 886 nt region of the Jhamt promoter. Conclusions This study reveals the detailed molecular mechanism of Egfr signaling in promoting JH biosynthesis in the German cockroach, shedding light on the intricate regulation of JH biosynthesis during insect development.

Chrysoperla nipponensis (Okamoto) displays typical adult reproductive diapause under short photoperiods; however, our understanding of the molecular mechanism underlying photoperiod-sensitive reproduction remains limited. In this study, we performed transcriptome profiling of four treatments (the diapause-sensitive stage and pre-diapause phase under long and short photoperiods) of C. nipponensis using RNA sequencing (RNA-seq). A total of 71,654 unigenes were obtained from the samples. Enrichment analysis showed that fatty acid metabolism-related pathways were altered under a short photoperiod. Moreover, β-oxidation-related gene expression was active during the diapause-sensitive period under a short photoperiod. The knockdown of juvenile hormone acid methyltransferase 1 (Jhamt1) prolonged the pre-oviposition period but did not affect the reproductive ability of female individuals in C. nipponensis. These findings provided us with a more comprehensive understanding of the molecular mechanisms of photoperiod-sensitive diapause and show that groundwork is crucial for bolstering the long-term storage and biocontrol potential of C. nipponensis.

Abstract The parasitic mite Varroa destructor devastates honey bee (Apis mellifera) colonies around the world. Entering a brood cell shortly before capping, the Varroa mother feeds on the honey bee larvae. The hormones 20‐hydroxyecdysone (20E) and juvenile hormone (JH), acquired from the host, have been considered to play a key role in initiating Varroa's reproductive cycle. This study focuses on differential expression of the genes involved in the biosynthesis of JH and ecdysone at six time points during the first 30 hr after cell capping in both drone and worker larvae of A. mellifera. This time frame, covering the conclusion of the honey bee brood cell invasion and the start of Varroa's ovogenesis, is critical to the successful initiation of a reproductive cycle. Our findings support a later activation of the ecdysteroid cascade in honey bee drones compared to worker larvae, which could account for the increased egg production of Varroa in A. mellifera drone cells. The JH pathway was generally downregulated confirming its activity is antagonistic to the ecdysteroid pathway during the larva development. Nevertheless, the genes involved in JH synthesis revealed an increased expression in drones. The upregulation of jhamt gene involved in methyl farnesoate (MF) synthesis came into attention since the MF is not only a precursor of JH but it is also an insect pheromone in its own right as well as JH‐like hormone in Acari. This could indicate a possible kairomone effect of MF for attracting the mites into the drone brood cells, along with its potential involvement in ovogenesis after the cell capping, stimulating Varroa's initiation of egg laying.

Aspongopuschinensis is a Chinese traditional edible and medicinal insect, which is in great demand in the society. This insect reproduces once a year which is caused by reproductive diapause resulting in insufficient production in wild resources. However, the mechanism of diapause in A. chinensis is still unclear. In this study, we focus on the relationship between juvenile hormones (JHs) and A. chinensis diapause. The results showed that JHIII concentration in diapause adult individuals was significantly lower than that in diapause termination adult individuals. When exogenous JHⅢ was injected into diapause adults, the rate of mating was increased significantly, development of the reproductive systems was accelerated, consumption of fat intensified, the expression of juvenile hormone acid o-methyl-transferase (JHAMT) was upregulated, and juvenile hormone epoxide hydrolase (JHEH) and fatty acid synthase (FAS) gene expressions were downregulated. In addition, RNAi of JHAMT decreased JH concentration, delayed the development of reproductive systems, slowed down fat consumption, and delayed the mean mating occurrence time significantly. Conversely, RNAi of JHEH resulted in an increased concentration of JH, development of reproductive systems was accelerated, consumption of fat was intensified, and mean mating occurrence time advanced significantly. Taken together, these findings uncovered that JH plays an important role in regulating reproductive diapause in A. chinensis and, thus, could provide a theoretical basis for further research on the diapause of A. chinensis.

Juvenile hormone (JH) plays a key role in preventing larval precocious metamorphosis, maintaining larval state, controlling adult sexual development and promoting insect egg maturation. Genetic studies have shown that POU factor ventral veins lacking regulates JH synthesis to control the timing of insect metamorphosis. However, how POU factor regulates JH synthesis is largely unknown. Here, we found POU-M2 was highly expressed in corpora allata (CA) and specifically localized in the nucleus of CA. The overexpression of POU-M2 promoted the expression of JH synthase genes and kr-h1 and enhanced the activity of JH synthase genes promoter. Further, POU-M2 promoted the transcription of JH acid O-methyltransferase (JHAMT) by directly binding to the key cis-regulatory elements -207, -249 and -453 within the proximal regions of JHAMT promoter. Both the POU domain and homeodomain were vital for the activation of POU-M2 on JHAMT transcription. Our study reveals the mechanism by which POU-M2 regulates JHAMT transcription.