Evaluation of inhibitor of apoptosis genes as targets for RNAi-mediated control of insect pests

Topical RNA Interference Induces Mortality in the Cotton-Melon Aphid Aphis gossypii with No Adverse Effect on the Predator Propylea japonica

The cotton-melon aphid (Aphis gossypii Glover), a globally distributed polyphagous pest, primarily infests cucurbit crops and leads to significant reductions in both crop yield and quality. Overreliance on chemical insecticides has resulted in widespread resistance development, highlighting the urgent requirement for alternative control strategies. This study evaluates the potential of topical RNA interference (RNAi) for managing cotton-melon aphids. We first analyzed instar-specific expression profiles of four candidate RNAi target genes (ATPE, IAP, Cat, and ilvE), employed topical dsRNA delivery to silence these genes, and subsequently evaluated their effects on aphid mortality, growth rates, and reproductive capacity. Furthermore, we investigated the non-target effects of RNAi-treated aphids on the predator ladybird beetles Propylea japonica. The results indicate that topical dsRNA delivery successfully silenced the target genes, significantly impairing aphid development and fecundity while inducing mortality, with no adverse effects on the beneficial predator. This method provides a powerful tool for insect gene functional studies and a promising solution for RNAi-based pest management.

Foliar spray double-stranded RNA targeting HvIAP1 induces high larval and adult mortality in Henosepilachna vigintioctopunctata

BACKGROUND

Exogenous double-stranded RNA (dsRNA) has the potential to serve as an effective alternative to conventional chemical pesticides for the control of insect pests, because it can specifically inhibit essential gene expression in these organisms. However, identifying suitable gene targets remains a crucial step in the development of RNA interference (RNAi)-based pest control strategies.

RESULTS

In this study, three apoptosis-related genes were selected to evaluate their potential for RNAi-induced lethality in Henosepilachna vigintioctopunctata via foliar spray dsRNAs. Our results revealed that silencing of HvIAP1 (inhibitor of apoptosis protein 1) had a significant lethal effect on larvae, whereas silencing of HvAIF1 and HvASPP1 did not, correlating with distinct expression patterns. Larvae ingested leaves sprayed with bacterially expressed dsHvIAP1 at a concentration of 100 ng/cm2 resulting in the impairment of cuticle tanning, cessation of feeding, and ultimately, 100% mortality within 7 days. In addition, the potential of dsHvIAP1 to mediate for adult control was also investigated and showed that administration of 200 ng/cm2 dsHvIAP1 resulted in 100% adult mortality within 9 days, accompanied by a significant reduction in leaf consumption and suppression of HvIAP1 expression compared with the dsGFP group.

CONCLUSIONS

Our findings demonstrate that HvIAP1 is a highly lethal molecular target with a notable difference in the concentration required for larval and adult mortality. These findings provide a foundation for the future development of RNAi pesticides for environmentally friendly control of H. vigintioctopunctata. © 2025 Society of Chemical Industry.

Persistent Parental RNAi in the Beetle Tribolium castaneum Involves Maternal Transmission of Long Double-Stranded RNA

Parental RNA interference (pRNAi) is a powerful and widely used method for gene-specific knockdown. Yet in insects its efficacy varies between species, and how the systemic response is transmitted from mother to offspring remains elusive. Using the beetle Tribolium castaneum, an RT-qPCR strategy to distinguish the presence of double-stranded RNA (dsRNA) from endogenous mRNA is reported. It is found that injected dsRNA is directly transmitted into the egg and persists throughout embryogenesis. Despite this depletion of dsRNA from the mother, it is shown that strong pRNAi can persist for months before waning at strain-specific rates. In seeking the receptor proteins for cellular uptake of long dsRNA into the egg, a phylogenomics profiling approach of candidate proteins is also presented. A visualization strategy based on taxonomically hierarchical assessment of orthology clustering data to rapidly assess gene age and copy number changes, refined by sequence-based evidence, is demonstrated. Repeated losses of SID-1-like channel proteins in the arthropods, including wholesale loss in the Heteroptera (true bugs), which are nonetheless highly sensitive to pRNAi, are thereby documented. Overall, practical considerations for insect pRNAi against a backdrop of outstanding questions on the molecular mechanism of dsRNA transmission for long-term, systemic knockdown are elucidated.

RNAi-Mediated Screening of Selected Target Genes Against Culex quinquefasciatus (Diptera: Culicidae)

Culex quinquefasciatus, a member of the Culex pipiens complex, is widespread in Saudi Arabia and other parts of the world. It is a vector for lymphatic filariasis, Rift Valley fever, and West Nile virus. Studies have shown the deleterious effect of RNA interference (RNAi)-mediated knockdown of various lethal genes in model and agricultural pest insects. RNAi was proposed as a tool for mosquito control with a focus on Aedes aegypti and Anopheles gambiae. In this study, we examined the effect of RNAi of selected target genes on both larval mortality and adult emergence of Cx. quinquefasciatus through two delivery methods: soaking and nanoparticles. Ten candidate genes were selected for RNAi based on their known lethal effect in other insects. Disruption of three genes, chitin synthase-1, inhibitor of apoptosis 1, and vacuolar adenosine triphosphatase, resulted in the highest mortality among the selected genes using the two treatment methods. Silencing the other seven genes resulted in a medium to low mortality in both assays. These three genes are also active against a wide range of insects and could be used for RNAi-based mosquito control in the future.

RNAi-based gene silencing in Phenacoccus solenopsis and its validation by in planta expression of a double-stranded RNA

BACKGROUND

Cotton is a cash crop majorly affected by many hemipteran pests, among them the cotton mealybug, Phenacoccus solenopsis. Cotton mealybug attack has a devastating effect on cotton production and causes huge yield losses.

RESULTS

In this study, 25 potential RNA interference (RNAi) target genes were selected from the iBeetle database and a transcriptome data set for P. solenopsis. To assess the effectiveness of the selected target genes, three methods were utilized to deliver double-stranded (ds)RNA (ingestion, artificial diet bioassay and transient gene silencing). dsRNA molecules at different concentrations were fed to insects and insect mortality was recorded for each target gene. Based on the mortality data, three genes, Krüppel homologue-1, ADP-ATP/Translocase and IDGF-1, were selected for further gene expression studies using a reduced concentration of dsRNA (5 μg/ml). Of the three genes, Krüppel homologue-1 showed significantly downregulated expression (by 70.81% and 84.33%) at two different time points (8 and 14 days). An RNAi silencing construct was designed for Krüppel homologue-1 under control of the double enhancer CamV35S promoter in the plant binary vector. Significant downregulation of gene expression, by 66.69% and 81.80%, was found for Krüppel homologue-1 using transient gene silencing at the same time intervals.

CONCLUSION

This work provides the first evidence for targeting the Krüppel homologue-1 gene in a hemipteran pest, P. solenopsis, using RNAi technology through oral delivery and in planta-based transient gene silencing methods. © 2020 Society of Chemical Industry.

Double-stranded RNAs targeting inhibitor of apoptosis gene show no significant cross-species activity

RNA interference (RNAi) has become an integral part of mainstream research due to its versatility and ease of use. However, the potential nontarget effects associated with double-stranded RNAs (dsRNA) are poorly understood. To explore this, we used dsRNAs targeting the inhibitor of apoptosis (iap) gene from nine insect species and assayed their possible nontarget effects. For each assay, we used a control (dsRNA targeting the gene coding for green fluorescent protein, GFP) and a species-specific dsRNA targeting nine iap genes in insect species to evaluate target gene knockdown efficiency, apoptosis phenotype in cells and mortality in insects. Our results revealed that dsIAP efficiently knocks down iap gene expression and induces apoptosis phenotype and mortality in target insect species. In contrast, no significant knockdown of the iap gene expression, apoptosis phenotypes, or mortality were detected in cell lines developed from nontarget insects or nontarget insects treated with dsIAPs. Interestingly, even among closely related insects such as stink bugs, Nezara viridula, Halyomorpha halys, and Murgantia histrionica, with substantial sequence similarity among iap genes from these insects, no significant nontarget effects of dsIAP were observed under the conditions tested. These data demonstrate no significant nontarget effects for dsIAPs and suggest that the threat of nontarget effects of RNAi technology may not be substantial.

Inhibitor of apoptosis is an effective target gene for RNAi-mediated control of Colorado potato beetle, Leptinotarsa decemlineata

The Colorado potato beetle (CPB; Leptinotarsa decemlineata) is one of the most notorious and difficult to control pests of potato and other solanaceous crops in North America. This insect has evolved a remarkable ability to detoxify both plant and synthetic toxins, allowing it to feed on solanaceous plants containing toxic alkaloids and to develop resistance to synthetic chemicals used for its control. RNA interference (RNAi) is a natural mechanism that evolved as an immune response to double-stranded RNA (dsRNA) viruses where dsRNA triggers silencing of target gene expression. RNAi is being developed as a method to control CPB. Here, we evaluated four CPB-specific genes to identify targets for RNAi-mediated control of this insect. Out of the four dsRNAs evaluated in CPB larvae and adults, dsIAP (dsRNA targeting inhibitor of apoptosis, iap gene) performed better than dsActin, dsHSP70, and dsDynamin in inducing larval mortality. However, in adults, the mortality induced by dsActin is significantly higher than the mortality induced by dsIAP, dsHSP70, and dsDynamin. Interestingly, a combination of dsIAP and dsActin performed better than either dsIAP or dsActin alone by inducing feeding inhibition in 24 hr and mortality in 48 hr in larvae. When the dsIAP and dsActin were expressed in the Escherichia coli HT115 strain and applied as a heat-killed bacterial spray on potato plants, it protected the plants from CPB damage. These studies show that the combination of dsIAP and dsActin shows promise as an insecticide to control CPB.