Silencing of vitellogenin gene contributes to the promise of controlling red palm weevil, Rhynchophorus ferrugineus (Olivier)

Functional characterization of vitellogenin unveils novel roles in RHBP uptake and lifespan regulation in the insect vector Rhodnius prolixus

In insects, vitellogenesis plays a critical role in providing the energy reserves needed for embryonic development as it ensures the accumulation of yolk in the oocytes. Vitellogenin (Vg), the precursor to vitellin (Vt), is primarily synthesized in the fat body of females and transported to the oocytes via receptor-mediated endocytosis. In Rhodnius prolixus, a key vector of Chagas disease, two Vg genes, Vg1 and Vg2, were characterized. These genes share 65 % amino acid identity and present the conserved Vitellogenin_N, DUF1943, and VWD domains typical of Vg proteins across various species. We found that Vg1 is expressed at significantly higher levels than Vg2 in adult females. Still, the expression of both isoforms was also detected in organs such as the flight muscle, midgut, and ovary, as well as in males and nymphs. RNAi-mediated knockdown of Vg1 and Vg2 in adult females resulted in the production of yolk-depleted eggs with drastically reduced levels of Vg and RHBP, the second most import yolk protein in this species. Despite regular oviposition rates, most of these eggs were inviable, highlighting the essential role of Vg and RHBP in embryo development. Although Vg expression was detected in adult males, the mating of Vg-knockdown males with wild-type females did not impact oviposition or egg viability, indicating that male Vg is not crucial for oogenesis in this species. Interestingly, Vg knockdown increased lifespan for both males and females, suggesting additional physiological functions beyond reproduction. These findings reveal the importance of Vg in oogenesis and embryonic development in R. prolixus while also suggesting potential non-reproductive roles of Vg in adult insect physiology.

A novel DUF 3472 domain-containing fern protein impairs reproduction in Helicoverpa armigera

Helicoverpa armigera is a polyphagous field crop insect pest. It poses a major threat to economically important crops leading to significant financial losses globally. Given the escalating resistance cases against chemical and Bt-based insecticides, there is an urgent need to identify new molecules to control this insect through different modes of action. In this endeavour, we have isolated a new protein [named Msc42] efficacious to H. armigera from the fern Microsorum scolopendria. The protein has two domains of unknown function- DUF 5077 and DUF 3472. At an LC50 of 3.6 μg/g, Msc42 severely impairs molting and metamorphosis in surviving larvae. Mass spectrometric analysis of the total soluble protein of larvae identified altered regulatory proteins responsible for impaired insect growth and reproduction. This includes larval cuticle proteins and endocuticle structural glycoproteins. Storage proteins were either at lower levels or below the detection threshold. Vitellogenins were also found deficient. The microscopic study showed that the fern protein ravaged ovarian follicle development leading to complete reproductive failure. Our results indicate that the novel fern protein Msc42 may offer an alternative strategy for controlling H. armigera.

Sprayable RNAi for silencing of important genes to manage red palm weevil, Rhynchophorus ferrugineus (Coleoptera: Curculionidae)

The red palm weevil, Rhynchophorus ferrugineus (Oliver, 1970) (Coleoptera: Dryophthoridae) is the most devastating insect-pest of palm trees worldwide. Synthetic insecticides are the most preferred tool for the management of RPW. Alternatively, RNA interference (RNAi) mediated silencing of crucial genes provides reasonable control of insect pests. Recently, we have targeted four important genes; ecdysone receptor (EcR), serine carboxypeptidase (SCP), actin and chitin-binding peritrophin (CBP) in the 3rd and 5th instar larvae RPW. The results from 20 days trial showed that the survival rate of 3rd instar larvae fed on SCP and actin dsRNAs exhibited the lowest survival (12-68%). While, in the 5th instar larvae, the lowest survival rate (24%) was recorded for SCP after 20 days of incubation. Similarly, the weight of the 3rd and 5th instar larvae treated with SCP and actin was significantly reduced to 2.30-2.36 g and 4.64-4.78 g after 6 days of dsRNA exposure. The larval duration was also decreased significantly in the larvae treated with all the dsRNA treatments. The qRT-PCR results confirmed a significant suppression of the targeted genes as 90-97% and 85-93% in the 3rd and 5th instar larvae, respectively. The results suggest that the SCP and the actin genes can be promising targets to mediate RNAi-based control of RPW.

De novo transcriptome assembly and differential gene expression analysis in different developmental stages of Agriotes sputator (click beetle)

Wireworms, the larva of click beetle (Agriotes species), are one of the most destructive pests of horticultural crops in North America, responsible for considerable economic losses in Canada. Agriotes sputator (A. sputator) species is a predominant wireworm pest attacking potato fields in Eastern Canada. However, no information about its genome-wide gene expression profile, specifically for the genes involved with development is available to date. Therefore, we generated the transcriptome profile of A. sputator during five developmental stages, including the three larval stages and adult male and female click beetle. Out of 714.7 million raw reads, de novo assembly generated 564,561 transcripts. The data were subjected to differential expression analysis using DESeq2, gene ontology, annotation, and pathway analyses. A total of 34,709 differentially expressed genes (DEGs) were significant (log2 fold change > 2, padj < 0.05) across the developmental stages. Functional analysis of DEGs identified development signaling, metabolism, transport, cellular mechanisms, and drug metabolism (cytochrome p450) pathways. This study provides comprehensive sequence resources and potential gene differences at different developmental stages of A. sputator. These findings will represent a major step towards developing sustainable methods to control this widely distributed pest in agricultural fields.

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.

Insights from different reproductive gene knockdowns via RNA interference in the lady beetle Eriopis connexa: Establishing a new model for molecular studies on natural enemies

Insect pest control can be achieved by the application of RNA interference (RNAi), a key molecular tool in functional genomics. Whereas most RNAi research has focused on insect pests, few studies have been performed on natural enemies. Validating the efficacy of RNAi in natural enemies is crucial for assessing its safety and enabling molecular research on these organisms. Here, we assessed the efficacy of RNAi in the ladybird beetle Eriopis connexa Germar (Coleoptera: Coccinellidae), focusing on genes related to reproduction, such as vitellogenin (Vg) and its receptor (VgR). In the transcriptome of E. connexa, we found one VgR (EcVgR) and two Vg genes (EcVg1 and EcVg2). These genes have been validated by in silico analyses of functional domains and evolutionary relationships. Five-day-old females were injected with 500 ng/µL of a specific double-stranded RNA (dsRNA) (dsEcVg1, dsEcVg2, or dsEcVgR) for RNAi tests, while nonspecific dsRNA (dsGFP or dsAgCE8.1) was used as a control. Interestingly, dsEcVg2 was able to knockdown both Vg genes, while dsEcVg1 could silence only EcVg1. Additionally, the viability of the eggs was significantly reduced when both Vg genes were knocked down at the same time (after treatment with dsEcVg2 or "dsEcVg1+dsEcVg2"). Ultimately, malformed, nonviable eggs were produced when EcVgR was silenced. Interestingly, no dsRNA treatment had an impact on the quantity of eggs laid. Therefore, the feasibility of RNAi in E. connexa has been confirmed, suggesting that this coccinellid is an excellent Neotropical model for molecular research on natural enemies and for studying RNAi nontarget effects.

Testosterone maintains male longevity and female reproduction in Chrysopa pallens

Vertebrate testosterone, an androgen present in the testes, is essential for male fertility. Vertebrate-type steroid hormones have been identified in insects, but their function remains unknown. Insect vitellogenin (Vg) is usually a female-specific protein involved in reproductive processes. However, males of some species, such as the green lacewing Chrysopa pallens, have Vg. Here, we demonstrated that the knockdown of C. pallens male Vg by RNAi significantly shortened the lifespan of males, suppressed the reproduction of post-mating females, and strikingly reduced the abundance of several immune-related compounds, including testosterone. LC-MS/MS revealed that C. pallens male testosterone had the same structure and molecular mass as vertebrate testosterone. Topical testosterone application partially restored the lifespan of Vg-deficient males and the reproduction of post-mating females. These results suggest that vertebrate-type testosterone maintains male longevity and female reproduction under the control of the male Vg in C. pallens.

Taxonomy, Biology, Symbionts, Omics, and Management of Rhynchophorus Palm Weevils (Coleoptera: Curculionidae: Dryophthorinae)

Palm weevils, Rhynchophorus spp., are destructive pests of native, ornamental, and agricultural palm species. Of the 10 recognized species, two of the most injurious species, Rhynchophorus ferrugineus and Rhynchophorus palmarum, both of which have spread beyond their native range, are the best studied. Due to its greater global spread and damage to edible date industries in the Middle East, R. ferrugineus has received more research interest. Integrated pest management programs utilize traps baited with aggregation pheromone, removal of infested palms, and insecticides. However, weevil control is costly, development of resistance to insecticides is problematic, and program efficacy can be impaired because early detection of infestations is difficult. The genome of R. ferrugineus has been sequenced, and omics research is providing insight into pheromone communication and changes in volatile and metabolism profiles of weevil-infested palms. We outline how such developments could lead to new control strategies and early detection tools.

IPS (In-Plant System) Delivery of Double-Stranded Vitellogenin and Vitellogenin receptor via Hydroponics for Pest Control in Diaphorina citri Kuwayama (Hemiptera: Psyllidae)

Diaphorina citri, a vector of citrus huanglongbing (HLB) disease, frequently leads to HLB outbreaks and reduces Rutaceae crop production. Recent studies have investigated the effects of RNA interference (RNAi) targeting the Vitellogenin (Vg4) and Vitellogenin receptor (VgR) genes, which are involved in egg formation in this pest, providing a theoretical foundation for developing new strategies to manage D. citri populations. This study presents RNAi methods for Vg4 and VgR gene expression interference and reveals that dsVgR is more effective than dsVg4 against D. citri. We demonstrated that dsVg4 and dsVgR persisted for 3-6 days in Murraya odorifera shoots when delivered via the in-plant system (IPS) and effectively interfered with Vg4 and VgR gene expression. Following Vg4 and VgR gene expression interference, egg length and width in the interference group were significantly smaller than those in the negative control group during the 10-30-day development stages. Additionally, the proportion of mature ovarian eggs in the interference group was significantly lower than that in the negative control group at the 10, 15, 20, 25, and 30-day developmental stages. DsVgR notably suppresses oviposition in D. citri, with fecundity decreasing by 60-70%. These results provide a theoretical basis for controlling D. citri using RNAi to mitigate the spread of HLB disease.

Transcriptional Regulation of Reproductive Diapause in the Convergent Lady Beetle, Hippodamia convergens

Simple Summary

Diapause is a dormant period typically controlled by daylength that ensures an insect’s survival through harsh environmental conditions. The convergent lady beetle, Hippodamia convergens, undergoes a reproductive diapause in winter, where female ovaries remain immature and no eggs are laid. This species is an important biological control agent, but during diapause, beetles are less likely to eat pest insects. Thus, knowledge of diapause mechanisms may facilitate manipulation thereof to improve biological control. Further, molecular studies of adult diapause and diapause in Coleoptera are relatively lacking. Here, we assembled and annotated a transcriptome for this species and quantified transcript expression changes during diapause. Female beetles were sampled at three times in diapause (early, mid, and late diapause), which allowed us to characterize the molecular processes occurring at distinct transitions throughout diapause. We found that transcripts involved in flight were consistently upregulated during diapause, which is consistent with dispersal flights at this stage, while transcripts involved in ovarian development were downregulated, which is consistent with the shutdown of reproduction in diapausing females. These findings identify key regulators of diapause in H. convergens and contribute to a growing body of literature on the molecular mechanisms of diapause across the insect phylogeny.

Abstract

Diapause is an alternate development program that synchronizes an insect’s life cycle with seasonally abundant resources and ensures survival in unfavorable conditions. The physiological basis of diapause has been well characterized, but the molecular mechanisms regulating it are still being elucidated. Here, we present a de novo transcriptome and quantify transcript expression during diapause in the convergent lady beetle Hippodamia convergens. H. convergens is used as an augmentative biocontrol agent, and adult females undergo reproductive diapause that is regulated by photoperiod. We sampled females at three stages (early, mid, and late diapause) and compared transcript expression to non-diapausing individuals. Based on principle component analysis, the transcriptomes of diapausing beetles were distinct from non-diapausing beetles, and the three diapausing points tended to cluster together. However, there were still classes of transcripts that differed in expression across distinct phases of diapause. In general, transcripts involved in muscle function and flight were upregulated during diapause, likely to support dispersal flights that occur during diapause, while transcripts involved in ovarian development were downregulated. This information could be used to improve biological control by manipulating diapause. Additionally, our data contribute to a growing understanding of the genetic regulation of diapause across diverse insects.