Interference Efficiency and Effects of Bacterium-mediated RNAi in the Fall Armyworm (Lepidoptera: Noctuidae)

Abstract

RNAi is an effective tool for gene function analysis and a promising strategy to provide environmentally friendly control approaches for pathogens and pests. Recent studies support the utility of bacterium-mediated RNAi as a cost-effective method for gene function study and a suitable externally applied delivery mechanism for pest control. Here, we developed a bacterium-mediated RNAi system in Spodoptera frugiperda based on four target genes, specifically, Chitinase (Sf-CHI), Chitin synthase B (Sf-CHSB), Sugar transporter SWEET1 (Sf-ST), and Hemolin (Sf-HEM). RNAi conducted by feeding larvae with bacteria expressing dsRNAs of target genes or injecting pupae and adults with bacterially synthesized dsRNA induced silencing of target genes and resulted in significant negative effects on growth and survival of S. frugiperda. However, RNAi efficiency and effects were variable among different target genes and dsRNA delivery methods. Injection of pupae with dsCHI and dsCHSB induced a significant increase in wing malformation in adults, suggesting that precise regulation of chitin digestion and synthesis is crucial during wing formation. Injection of female moths with dsHEM resulted in lower mating, fecundity, and egg hatching, signifying a critical role of Sf-HEM in the process of egg production and/or embryo development. Our collective results demonstrate that bacterium-mediated RNAi presents an alternative technique for gene function study in S. frugiperda and a potentially effective strategy for control of this pest, and that Sf-CHI, Sf-CHSB, Sf-ST, and Sf-HEM encoding genes can be potent targets.

A Versatile Hemolin With Pattern Recognitional Contributions to the Humoral Immune Responses of the Chinese Oak Silkworm Antheraea pernyi

“…The mRNA level of hemolin was significantly increased in response to bacterial stimulation but unaffected by natural baculoviral infection in the fat bodies and hemocytes of noctuid moths ( 17 ), while an opposite result was reported in bombycoid moths in which both bacterial and baculovirus infection led to upregulation of hemolin in A. pernyi ( 41 ). In addition to pathogen infection, hemolin was also present at a very low level in many vital organs, the concentration of which increased dramatically at metamorphosis stages in the absence of microbial challenge and regulated by hormones ( 19 , 23 , 24 , 42 ). In the wandering 5 th instar larval stage of Plodia interpunctella , major expression of hemolin was detected in the epidermis, rather than in the fat body or gut, and the level was increased by feeding with RH-5992 (an ecdysteroid agonist) but reduced by treatment with KK-42 (an ecdysteroid inhibitor), suggesting that hemolin probably protected larvae from potential infection in the wandering stage ( 15 ).…”

“…Further investigations of the deduced amino acid sequence and crystal structure reveal that hemolin in H. cecropia has a close relation to insect and vertebrate neural adhesion molecules and arranges four internal repeated C2-type Ig domains into a strongly bent horseshoe structure ( 10 , 12 ). Over the past few decades, numerous hemolin homologs have been identified, and their expression properties have been well studied in insects ( 13 – 19 ). The mRNA expression of insect hemolins is found in several tissues over almost all stages of development, in which the expression level intriguingly increases during metamorphosis, diapause ( 20 ) and molting periods ( 21 – 24 ).…”

Methods for the Cost-Effective Production of Bacteria-Derived Double-Stranded RNA for in vitro Knockdown Studies

“…The system is mainly used for direct feeding of induced bacteria to research animals in a process termed bacterium-mediated RNA interference (bmRNAi) ( Timmons and Fire, 1998 ; Goodfellow et al, 2019 ; Kunte et al, 2020 ). Recent publications reaffirm its useability in the important lepidopteran pest genera Spodoptera and Helicoverpa ( Vatanparast et al, 2021 ; Wan et al, 2021 ; Wang et al, 2021 ).…”

“…This approach is however unpractical in Helicoverpa pests due to the immune responses generated upon the presence of bacteria in the hemolymph ( Li et al, 2019 ). Injections of HT115 bacteria-derived dsRNA extracted using commercial kits was shown to be effective at inducing target gene knockdowns in a lepidopteran species ( Wan et al, 2021 ). As a result, research has focused on developing a cost-effective protocol for the isolation of dsRNA from the bacterial cells.…”

Five Visual and Olfactory Target Genes for RNAi in Agrilus Planipennis

“…Due to the high specificity and efficiency of RNAi, more and more research groups tried to develop new pest control methods based on this technology and the latest research results showed that inhibiting the expression of important genes in the growth and development process of insects could cause growth and development disorders or death of insects. Many relevant target genes were screened, such as the inhibitor of apoptosis (IAP), vacuolar sorting protein SNF7 (SNF7), and snakeskin (SSK) of Anoplophora glabripennis (Dhandapani et al, 2020); the chitinase (Sf-CHI), chitin synthase B (Sf-CHSB), sugar transporter SWEET1 (Sf-ST), and hemolin (Sf-HEM) of Spodoptera frugiperda (Wan et al, 2021); the leucine-rich repeat-containing (LGR2) of Hyphantria cunea (Sun et al, 2021) and so on. All of above is the strong evidence that RNAi can be used as a new method for pest control.…”