Food source affects the expression of vitellogenin and fecundity of a biological control agent, Neoseiulus cucumeris

The ZcVg3 Gene Regulates the Reproduction and Lifespan of Female Zeugodacus cucurbitae (Coquillett) Mediated by Short-Term High Temperatures

Zeugodacus cucurbitae (Coquillett) is a significant pest affecting fruit and vegetables in tropical and subtropical regions, and its development and reproduction are enhanced after exposure to short-term high-temperature stress at 45 °C. Vitellogenin (Vg) is an essential precursor of yolk protein formation in eggs and plays a vital role in the ovarian development of insects. Interfering with the Z. cucurbitae vitellogenin receptor (ZcVgR) gene in short-term high-temperature conditions decreases the fecundity of female adults, while the transcription level of the ZcVg3 gene increases. To elucidate the reproductive function of the ZcVg3 gene and the synergistic relationship among the ZcVgs genes under short-term high temperatures, this study injected siRNA to interfere with the ZcVg3 gene after subjecting Z. cucurbitae to a 1 h treatment at 45 °C and 25 °C. The expression of the ZcVg3 gene was suppressed, leading to the upregulation of the ZcVg1 and ZcVg2 genes, and the expression of the ZcVgR gene was initially decreased and then increased. Silencing the ZcVg3 gene after a 1 h treatment at 45 °C resulted in a reduction of approximately 84.7% and 75.9% in the fecundity and spawning days of female adults compared to the control. The development rate of their ovaries and the ovarian diameter significantly decreased, and their lifespan was reduced by 71%. The ZcVg3 gene plays a crucial role in the reproduction of Z. cucurbitae in short-term high-temperature conditions. The results of this study provide potential targets for the development of RNAi-based techniques for the control of Z. cucurbitae.

Peroxisome biogenesis factor PEX14 is crucial for survival and fecundity of female brown planthopper, Nilaparvata lugens (Stål)

Peroxisomes are ubiquitous cellular organelles participating in a variety of critical metabolic reactions. PEX14 is an essential peroxin responsible for peroxisome biogenesis. In this study, we identified the human PEX14 homolog in the brown planthopper, Nilaparvata lugens (Hemiptera: Delphacidae). N. lugens PEX14 (NlPEX14) showed significant topological similarity to its human counterpart. It is expressed throughout all developmental stages, with the highest expression observed in adult insects. Down-regulation of NlPEX14 through injection of NlPEX14-specific double-strand RNA impaired nymphal development. Moreover, females subjected to dsNlPEX14 treatment exhibited a significantly reduced lifespan. Additionally, we found abnormal ovarian development and a significant decrease in the number of eggs laid in NlPEX14-downregulated females. Further experiments support that the shortening of lifespan and the decrease in female fecundity can be attributed, at least partially, to the accumulation of fatty acids and reduced expression of vitellogenin. Together, our study reveals an indispensable function of NlPEX14 for insect reproduction and establishes a causal connection between the phenotypes and peroxisome biogenesis, shedding light on the importance of peroxisomes in female fecundity.

Star Polycation Mediated dsRNA Improves the Efficiency of RNA Interference in Phytoseiulus persimilis

RNA interference (RNAi) is one of the most widely used techniques to study gene functions. There is still a lack of RNAi techniques that can be applied in Phytoseiidae conveniently and efficiently. Star Polycation is a new nanomaterial commonly used as a carrier of dsRNA in RNAi. Five genes of P. persimilis (PpATPb, PpATPd, PpRpL11, PpRpS2, and Pptra-2) were selected to verify whether SPc promotes the delivery of dsRNA into P. persimilis through soaking. When each of the five genes were interfered using SPc-mediated dsRNA, the total number of success offspring produced per female in six days decreased by ca. 92%, 92%, 91%, 96%, and 64%. When PpATPb, PpATPd, PpRpL11, or PpRpS2 was interfered, both the fecundity and egg hatching rate decreased. In contrast, when Pptra-2 was interfered, reduction in the reproductive capability was mainly the result of the decreased egg hatching rate. Correspondingly, when the target gene was interfered, P. persimilis expression of PpRpL11 reduced by 63.95%, while that of the other four genes reduced by at least 80%. Our studies showed that nanomaterials, such as SPc, have the potential to be used in RNA interference of phytoseiid mites.

Effect of Insulin Receptor on Juvenile Hormone Signal and Fecundity in Spodoptera litura (F.)

Simple Summary

The tobacco cutworm, Spodoptera litura (F.), exemplifies strong reproductive capacities and damages many agricultural crops. The insulin signaling pathway is known as a key determinant of female reproduction in insects. However, the detailed molecular mechanisms in these processes are poorly studied. Here, we injected bovine insulin into the newly emerged moth, resulting in gene expression changes in the insulin pathway, while knockdown of SlInR caused an inverse gene expression change involved in the insulin pathway. Further studies indicated that the content of JH-III, Vg, total proteins and triacylgycerol could be suppressed by SlInR dsRNA injection. Furthermore, stunted ovaries and lower fecundity were observed by RNAi. Our studies indicated that SlInR plays a key role in JH-III synthesis and the ovarian development in S. litura.

Abstract

Insulin signaling can regulate various physiological functions, such as energy metabolism and reproduction and so on, in many insects, including mosquito and locust. However, the molecular mechanism of this physiological process remains elusive. The tobacco cutworm, Spodoptera litura, is one of the most important pests of agricultural crops around the world. In this study, phosphoinositide 3-kinase (SlPI3K), protein kinase B (SlAKT), target of rapamycin (SlTOR), ribosomal protein S6 kinase (SlS6K) and transcription factor cAMP-response element binding protein (SlCREB) genes, except transcription factor forkhead box class O (SlFoxO), can be activated by bovine insulin injection. Then, we studied the influence of the insulin receptor gene (SlInR) on the reproduction of S. litura using RNA interference technology. qRT-PCR analysis revealed that SlInR was most abundant in the head. The SlPI3K, SlAKT, SlTOR, SlS6K and SlCREB genes were decreased, except SlFoxO, after the SlInR gene knockdown. Further studies revealed that the expression of vitellogenin mRNA and protein, Methoprene-tolerant gene (SlMet), could be down-regulated by the injection of dsRNA of SlInR significantly. Furthermore, a depletion in the insulin receptor by RNAi significantly decreased the content of juvenile hormone III (JH-III), total proteins and triacylgycerol. These changes indicated that a lack of SlInR could impair ovarian development and decrease fecundity in S. litura. Our studies contribute to a comprehensive insight into reproduction, regulated by insulin and the juvenile hormone signaling pathway through nutrition, and a provide theoretical basis for the reproduction process in pest insects.

Characterization of MicroRNAs Associated with Reproduction in the Brown Planthopper, Nilaparvata lugens

Insects have a robust capacity to produce offspring for propagation, and the reproductive events of female insects have been achieved at the molecular and physiological levels via regulatory gene pathways. However, the roles of MicroRNAs (miRNAs) in the reproductive development of the brown planthopper (BPH), Nilaparvata lugens, remain largely unexplored. To understand the roles of miRNAs in reproductive development, miRNAs were identified by Solexa sequencing in short-winged (SW) female adults of BPH. Small RNA libraries derived from three developmental phases (1 day, 3 days, and 5 days after emergence) were constructed and sequenced. We identified 905 miRNAs, including 263 known and 642 novel miRNAs. Among them, a total of 43 miRNAs were differentially expressed in the three developmental phases, and 14,568 putative targets for 43 differentially expressed miRNAs (DEMs) were predicted by TargetScan and miRanda. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis of the predicted miRNA targets illustrated the putative roles for these DEMs in reproduction. The progress events were annotated, including oogenesis, lipid biosynthetic process, and related pathways such as apoptosis, ABC transporters, and amino acid metabolism. Four highly abundant DEMs (miR-9a-5p, miR-34-5p, miR-275-3p, and miR-317-3p) were further screened, and miR-34-5p was confirmed to be involved in the regulation of reproduction. Overexpression of miR-34-5p via injecting its mimics reduced fecundity and decreased Vg expression. Moreover, target genes prediction for miR-34-5p showed they might be involved in 20E signaling cascades, apoptosis, and gonadal development, including hormone receptor 4 (HR4), caspase-1 (Cp-1), and spermatogenesis-associated protein 20 (SPATA20). These findings provide a valuable resource for future studies on the role of miRNAs in BPH reproductive development.

Molecular characterization, expression, and function of Vitellogenin genes in Phytoseiulus persimilis

Vitellogenin (Vg) is an important factor that impacts oocyte maturation, egg formation and embryonic development in Arthropoda. Two orthologs of Vg gene were obtained from the genome of Phytoseiulus persimilis and termed as PpVg1 and PpVg2. Both orthologs belong to the large lipid transfer protein superfamily. The expression of PpVg1 and PpVg2 was low in immatures and male adults, and increased rapidly in female adults after mating, and reached a peak before the first egg was laid (168×  and 20.5×  the level in virgin females, respectively). When PpVg1 and PpVg2 were interfered with dsRNA, the relative expression decreased by 81.0 and 30.9%, respectively, and 7.8 and 31.4% interfered individuals died within 24 h. Among surviving individuals, ca. 51.1 and 44.8% are infertile. Factors that might be related to expression of Vg genes are also discussed.

Genomic insights into mite phylogeny, fitness, development, and reproduction

BACKGROUND

Predatory mites (Acari: Phytoseiidae) are the most important beneficial arthropods used in augmentative biological pest control of protected crops around the world. However, the genomes of mites are far less well understood than those of insects and the evolutionary relationships among mite and other chelicerate orders are contested, with the enigmatic origin of mites at one of the centres in discussion of the evolution of Arachnida.

RESULTS

We here report the 173 Mb nuclear genome (from 51.75 Gb pairs of Illumina reads) of the predatory mite, Neoseiulus cucumeris, a biocontrol agent against pests such as mites and thrips worldwide. We identified nearly 20.6 Mb (~ 11.93% of this genome) of repetitive sequences and annotated 18,735 protein-coding genes (a typical gene 2888 bp in size); the total length of protein-coding genes was about 50.55 Mb (29.2% of this assembly). About 37% (6981) of the genes are unique to N. cucumeris based on comparison with other arachnid genomes. Our phylogenomic analysis supported the monophyly of Acari, therefore rejecting the biphyletic origin of mites advocated by other studies based on limited gene fragments or few taxa in recent years. Our transcriptomic analyses of different life stages of N. cucumeris provide new insights into genes involved in its development. Putative genes involved in vitellogenesis, regulation of oviposition, sex determination, development of legs, signal perception, detoxification and stress-resistance, and innate immune systems are identified.

CONCLUSIONS

Our genomics and developmental transcriptomics analyses of N. cucumeris provide invaluable resources for further research on the development, reproduction, and fitness of this economically important mite in particular and Arachnida in general.

Influence of food availability on mate-guarding behaviour of ladybirds

A recent study on ladybird, Menochilus sexmaculatus (Fabricius) demonstrates that males perform post-copulatory mate guarding in the form of prolonged mating durations. We investigated whether food resource fluctuation affects pre- and post-copulatory behaviour of M. sexmaculatus. It has not been studied before in ladybirds. For this, adults were subjected to prey resource fluctuations sequentially at three levels: post-emergence (Poe; 10 days), pre-mating (Prm; 24 h) and post-mating (Pom; 5 days; only female). The food resource conditions at each level could be any one of scarce, optimal or abundant. Pre-copulatory and post-copulatory behaviour, and reproductive output were assessed. Post-emergence and pre-mating nutrient conditions significantly influenced the pre-copulatory behaviour. Males reared on scarce post-emergence conditions were found to require significantly higher number of mating attempts to establish mating unlike males in the other two food conditions. Under scarce post-emergence and pre-mating conditions, time to commencement of mating and latent period were high but opposite result was obtained for mate-guarding duration. Fecundity and per cent egg viability were more influenced by post-mating conditions, with scarce conditions stopping oviposition regardless of pre-mating and post-emergence conditions. Present results indicate that pre- and post-copulatory behaviour of ladybird is plastic in nature in response to food resource fluctuations.

The fenpropathrin resistant Tetranychus cinnabarinus showed increased fecundity with high content of vitellogenin and vitellogenin receptor

Carmine spider mite, Tetranychus cinnabarinus (Boisduval), an agricultural pest of economically important crops, has developed resistance to a group of pesticides. We have selected a fenpropathrin-resistant strain (FeR) of T. cinnabarinus from the isogenous and susceptible strain (SS), and found that the FeR not only showed resistance but its fecundity also increased. According to the numbers of eggs laid per day of both strains, the FeR was more fertile than SS throughout the life span. To investigate the underlying reason, the protein contents of vitellogenin (vg) and vitellogenin receptor (vgr) were detected, and the results showed both of them were significantly higher in FeR than in SS. Then, the mRNA-expressions of vg and vgr genes were compared between FeR and SS. From the transcriptome data of T. cinnabarinus, we classified two vg genes (designated as Tcvg1 and Tcvg2, respectively) and a vgr gene (designated as Tcvgr). The expressions of Tcvg1, Tcvg2 and Tcvgr were highly associated with the fecundity of the mites that their mRNAs were extremely abundant at the adult stage, but hardly detectable during the developmental period (from egg to deutonymph). In accordance with the protein content, the expression levels of the three genes were all significantly higher in FeR than they were in SS. These results suggested that after resistance selection with fenpropathrin in T. cinnabarinus, the fecundity and the expression of reproduction-related genes (vg and vgr) were significantly higher in fenpropathrin resistant strain than that in susceptible strain.

Functional screen for microRNAs of Nilaparvata lugens reveals that targeting of glutamine synthase by miR-4868b regulates fecundity

Insect fecundity is regulated by the interaction of genotypes and the environment. MicroRNAs (miRNAs) also act in insect development and reproduction by regulating genes involved in these physiological processes. Although hundreds of insect miRNAs have been identified, the biological roles of most remain poorly understood. Here, we used a multi-algorithm approach for miRNA target prediction in 3'UTRs of fecundity-related genes in the brown planthopper (BPH) Nilaparvata lugens and identified 38 putative miRNAs targeting 9 fecundity-related genes. High-ranked miRNAs were selected for target validation. Using a dual luciferase reporter assay in S2 cells, we experimentally verified N. lugens glutamine synthetase (NlGS) as an authentic target of microRNA-4868b (miR-4868b). In the females, NlGS protein expression was down-regulated after injection of a miR-4868b mimic but up-regulated after injection of a miR-4868b inhibitor. In addition, overexpression of miR-4868b reduced fecundity, and disrupted ovary development and Vg expression in N. lugens. These findings showed that miR-4868b is involved in regulating N. lugens fecundity by targeting NlGS. Moreover, this study may lead to better understanding of the fecundity of this important agricultural insect pest.

Expression analysis of Drosophila doublesex, transformer-2, intersex, fruitless-like, and vitellogenin homologs in the parahaploid predator Metaseiulus occidentalis (Chelicerata: Acari: Phytoseiidae)

Characterization and expression analyses are essential to gain insight into sex-determination pathways in members of the Acari. Little is known about sex determination at the molecular level in the western orchard predatory mite Metaseiulus occidentalis (Arthropoda: Chelicerata: Arachnida: Acari: Phytoseiidae), a parahaploid species. In this study, eight genes previously identified as putative homologs to genes involved in the sex-determination pathway in Drosophila melanogaster were evaluated for sex-specific alternative splicing and sex-biased expression using reverse-transcriptase PCR and quantitative real-time PCR techniques, respectively. The homologs evaluated in M. occidentalis included two doublesex-like genes (Moccdsx1 and Moccdsx2), transformer-2 (Mocctra-2), intersex (Moccix), two fruitless-like genes (MoccBTB1 and MoccBTB2), as well as two vitellogenin-like genes (Moccvg1 and Moccvg2). Single transcripts of equal size were detected in males and females for Moccdsx1, Moccdsx2, Mocctra-2, Moccix, and MoccBTB2, suggesting that their pre-mRNAs do not undergo alternative splicing in a sex-specific manner. Three genes, Moccdsx1, Moccdsx2 and MoccBTB2, displayed male-biased expression relative to females. One gene, Moccix, displayed female-biased expression relative to males. Two genes, Mocctra-2 and MoccBTB1, did not display detectable differences in transcript abundance in males and females. Expression of Moccvg1 and Moccvg2 were detected in females only, and transcript levels were up-regulated in mated females relative to unmated females. To our knowledge, this represents the first attempt to elucidate expression patterns of putative sex-determination genes in an acarine. This study is an initial step towards understanding the sex-determination pathway in the parahaploid M. occidentalis.