Molecular Identification and Functional Characterization of Vitellogenin Receptor From Harmonia axyridis (Coleoptera: Coccinellidae)

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.

Pannier is a key regulator of embryogenesis, pupal development and female reproduction in the insect pest Bactrocera dorsalis

BACKGROUND

Most arthropods are famous for their large reproductive capacity, with the ovary playing a vital role in the process. The study of the regulatory mechanisms of ovarian development may have the potential for a reproduction-based pest management strategy. GATA-binding transcription factors (GATAs) as important regulatory factors mediate many physiological processes, including development, immunity, insecticide resistance and reproduction. The Pannier (pnr), a member of GATA family, was confirmed to be involved in ovarian development of Bactrocera dorsalis in our previous study. However, the direct evidence of pnr regulating the fly ovarian development is still lacking.

RESULTS

We used CRISPR/Cas9 to create Bdpnr loss-of-function mutations. Homozygous Bdpnr^-/- mutants were nonviable, with most individuals dying during embryogenesis, some surviving to the larval stages, and the remaining few dying during pupation. In contrast, heterozygous individuals reached the adult stage, but ovarian development was disrupted, with concomitant decreases in egg laying and hatching rates. We also found that two genes encoding vitellogenin proteins (BdVg1 and BdVg2) and the vitellogenin receptor (BdVgR) were significantly down-regulated in heterozygous mutants compared to wild-type controls.

CONCLUSION

These results indicate that Bdpnr is required for embryonic and post-embryonic development, including the formation of ovaries. Bdpnr could therefore be considered as a molecular target for tephritid fly pest control. © 2022 Society of Chemical Industry.

Molecular Characterization of Vitellogenin and Its Receptor in Spodoptera frugiperda (J. E. Smith, 1797), and Their Function in Reproduction of Female

The fall armyworm Spodoptera frugiperda is a highly polyphagous invasive pest. The strong reproductive capacity is an important factor in the rapid colonization and expansion of S. frugiperda. Vitellogenin (Vg) and vitellogenin receptor (VgR) play important roles in insect reproduction. As the precursor of vitellin (Vn), Vg provides essential nutrition for embryonic development, and VgR mediates the uptake of Vg by oocytes. In this context, we cloned and characterized these two genes of S. frugiperda (SfVg and SfVgR) and evaluated their expression profiles in different developmental stages and tissues. The RNA interference experiment was used to investigate their function in vitellogenesis. The ORF values of SfVg and SfVgR were 5250 and 5445 bp, encoding 1749 and 1815 amino acid residues, respectively. The qRT-PCR results revealed that both SfVg and SfVgR were highly expressed in female adults; SfVg was specifically expressed in the fat body, whereas SfVgR was highly expressed in the ovary. In addition, the depletion of either SfVg or SfVgR hindered oocyte maturation and ovarian development, leading to a significant decrease in fecundity. The present study reveals the importance of SfVg and SfVgR in the vitellogenesis of S. frugiperda, laying a theoretical foundation for the development of pollution-free pest control strategies with SfVg and SfVgR as new targets.

Function of Vitellogenin receptor gene in reproductive regulation of Zeugodacus cucurbitae (Coquillett) after short-term high-temperature treatment

Climate change has increased the frequency of extreme heat events. Zeugodacus cucurbitae (Coquillett) is an important tropical pest that typically changes its reproductive strategies in response to extremely high temperatures. Newly emerged adults of three consecutive generations (F₁, F₂, and F₃) of Z. cucurbitae (Coquillett) were exposed to 25°C, 33°C, 37°C, 41°C, and 45°C treatments for 1 h to clarify the effects of short-term high temperatures on its reproduction. The influence of these temperatures on reproduction was evaluated using indicators, such as egg number. Newly emerged adults were exposed to 25°C and 45°C treatments for 1 h, and the expression of Vitellogenin receptor (VgR) gene in females was interfered with siRNA, and silencing efficiency of RNAi was evaluated. Results showed that short-term high temperatures, except for F₁ treated at 45°C for 1 h to stimulate oviposition, exert a general adverse effect on the reproduction of Z. cucurbitae (Coquillett). All F₃ died after the 45°C treatment for 1 h. Silencing of the VgR gene resulted in the significant downregulation of VgR gene expression at both 24 and 72 h. The egg number, oviposition days, and hatchability of eggs were significantly lower than those of other treatment groups after interference, and the inhibition effect of egg number was the most evident, with a decrease of 88.4% and 95.2% at 25°C and 45°C, respectively, compared with that of the Control Check (CK). Ovarian development speed and diameter were also significantly lower than those of other treatment groups after the interference. The results of this study can provide a theoretical reference for the integrated control of Z. cucurbitae (Coquillett) during high-temperature seasons.