Silencing T-type voltage-gated calcium channel gene reduces the sensitivity of Tetranychus cinnabarinus (Boisduval) to scopoletin

Functional analysis of a down-regulated transcription factor-SoxNeuroA gene involved in the acaricidal mechanism of scopoletin against spider mites

BACKGROUND

Insight into the mode of action of plant-derived acaricides will help in the development of sustainable control strategies for mite pests. Scopoletin, a promising plant-derived bioactive compound, displays prominent acaricidal activity against Tetranychus cinnabarinus. The transcription factor SoxNeuroA plays a vital role in maintaining calcium ion (Ca2+ ) homeostasis. Down-regulation of SoxNeuroA gene expression occurs in scopoletin-exposed mites, but the functional role of this gene remains unknown.

RESULTS

A SoxNeuroA gene from T. cinnabarinus (TcSoxNeuroA) was first cloned and identified. Reverse transcription polymerase chain reaction (RT-PCR), quantitative real-time polymerase chain reaction (qPCR), and Western blotting assays all confirmed that the gene expression and protein levels of TcSoxNeuroA were significantly reduced under scopoletin exposure. Furthermore, RNA interference silencing of the weakly expressed SoxNeuroA gene significantly enhanced the susceptibility of mites to scopoletin, suggesting that the acaricidal mechanism of scopoletin was mediated by the weakly expressed SoxNeuroA gene. Additionally, yeast one-hybrid (Y1H) and dual-luciferase reporter assays revealed that TcSoxNeuroA was a repressor of Orai1 Ca2+ channel gene transcription, and the key binding sequence was ATCAAAG (positions -361 to -368 of the Orai1 promoter). Importantly, site-directed mutagenesis and microscale thermophoresis assays further indicated that ASP185, ARG189, and LYS217, which were key predicted hydrogen-bonding sites in the molecular docking model, may be the vital binding sites for scopoletin in TcSoxNeuroA.

CONCLUSION

These results demonstrate that the acaricidal mechanism of scopoletin involves inhibition of the transcription factor SoxNeuroA, thus inducing the activation of the Orai1 Ca2+ channel, eventually leading to Ca2+ overload and lethality. Elucidation of the transcription factor-targeted mechanism for this potent plant-derived acaricide has vital implications for the design of next-generation green acaricides with novel targets. © 2023 Society of Chemical Industry.

Efficacy of essential oils of Egletes viscosa and Lippia schaueriana on the reproductive biology of Rhipicephalus sanguineus sensu lato engorged females

The study analyzed the chemical composition and the acaricide effect of Egletes viscosa Less (macela-da-terra) and Lippia schaueriana Mart. (lipia-da-serra) essential oils (EOs) on Rhipicephalus sanguineus s. l. (Acari: Ixodidae) engorged females. The chemical analysis (GC-MS and GC-FID) identified 27 components in E. viscosa EO and 18 in L. schaueriana EO, which comprise more than 98% of its constituents. The effects of the oils on the reproductive biology of R. sanguineus ticks were assessed by adult immersion test. Both EOs significantly reduced (p < 0.05) the egg production index when the females were exposed to 25 and 50 mg/mL, also affecting the egg viability. During the laying process, the eggs produced by the females exposed to the EO showed several morphological alterations such as dehydrated, darkened, and disaggregated, and these alterations were more severe as the concentrations increased. The mortality percentages were 58.9%, 70.8% and 92.7% when the ticks were exposed to 12.5, 25 and 50 mg/mL of E. viscosa oil, respectively. In the same concentrations, the efficacy of L. schaueriana was 39.3%, 53.4%, and 84.6%. Therefore, it can be concluded that the essential oils of E. viscosa and L. schaueriana have acaricidal effect in females of R. sanguineus s.l ticks.

The Insecticidal Efficacy and Physiological Action Mechanism of a Novel Agent GC16 against Tetranychus pueraricola (Acari: Tetranychidae)

Simple Summary

Spider mite is major pest in agriculture and have developed resistance to commonly used pesticides. Therefore, it is urgent to discover new pesticides to control the pest. In order to provide alternatives for its management, we evaluated the effectiveness of a new agent GC16 against the spider mite Tetranychus pueraricola. Then, we preliminarily revealed the its acaricidal mechanism of action based on the damage of cuticle and organelles of mites. We confirmed that GC16 has a good controlling effect on T. pueraricola and it is not harmful to Picromerus lewisi and Harmonia axyridis. Our research provides not only an alternative pesticide for the management of spider mites, but also guidance for the application of GC16 in sustainable agriculture.

Abstract

Chemical control plays a crucial role in pest management but has to face challenges due to insect resistance. It is important to discover alternatives to traditional pesticides. The spider mite Tetranychus pueraricola (Ehara & Gotoh) (Acari: Tetranychidae) is a major agricultural pest that causes severe damage to many crops. GC16 is a new agent that consists of a mixture of Calcium chloride (CaCl₂) and lecithin. To explore the acaricidal effects and mode of action of GC16 against T. pueraricola, bioassays, cryogenic scanning electron microscopy (cryo-SEM) and transmission electron microscopy (TEM) were performed. GC16 had lethal effects on the eggs, larvae, nymphs, and adults of T. pueraricola, caused the mites to dehydrate and inactivate, and inhibited the development of eggs. GC16 displayed contact toxicity rather than stomach toxicity through the synergistic effects of CaCl₂ with lecithin. Cryo-SEM analysis revealed that GC16 damaged T. pueraricola by disordering the array of the cuticle layer crest. Mitochondrial abnormalities were detected by TEM in mites treated by GC16. Overall, GC16 had the controlling efficacy on T. pueraricola by cuticle penetration and mitochondria dysfunction and had no effects on Picromerus lewisi and Harmonia axyridis, indicating that GC16 is likely a new eco-friendly acaricide.

Effects of RNAi-mediated plasma membrane calcium transporting ATPase and inositol 1,4,5-trisphosphate receptor gene silencing on the susceptibility of Mythimna separata to wilforine

Wilforine, a compound of sesquiterpene alkaloids isolated from Tripterygium wilfordii, exhibits excellent insecticidal activity against Mythimna separata. In order to clarify the action mechanism of wilforine, the plasma membrane calcium transporting ATPase (PMCA) and inositol 1,4,5-trisphosphate receptor (IP₃R) from M. separata were studied. Results showed that the open reading frame of MsIP₃R and MsPMCA were 8118 bp and 3438 bp in length, as well as encoded 2706 and 1146 amino acids, respectively. Multiple sequence alignment and phylogenetic analysis revealed that the MsIP₃R and MsPMCA had high homology with the IP₃R and PMCA of other insects, but had low similarity with those of mammals, which means the IP₃R and PMCA have potential to be the novel targets of insecticides with high selectivity between mammals and insects. Both MsIP₃R and MsPMCA genes existed throughout the life cycle of M. separata, and were all predominantly expressed in somatic muscle of fifth-instar larvae and the adults. The susceptibilities of PMCA-silenced M. separata to wilforine were significantly lower than that of the normal M. separata, which illustrates that PMCA could be one of the targets of wilforine. However, the susceptibilities of IP₃R-silenced M. separata to wilforine did not change significantly compared with the susceptibilities of normal M. separata, which shows that wilforine may not interact with the IP₃R protein. These findings provide clues for elucidating the insecticidal mechanism of wilforine.