Background: The western flower thrips Frankliniella occidentalis is an insect pest that damages various crops, including hot peppers. It is a vector of a plant pathogen, tomato spotted wilt virus. To control this pest, chemical insecticides have been used in the past, but the control efficacy is unsatisfactory owing to rapid resistance development by F. occidentalis. Methodology: : This study reports a novel control technology against this insect pest using RNA interference (RNAi) of the vacuolar-type ATPase (vATPase) expression. Eight subunit genes (vATPase-A ∼ vATPase-H) of vATPase were obtained from the F. occidentalis genome and confirmed for their expressions at all developmental stages. Results: Double-stranded RNAs (dsRNAs) specific to the eight subunit genes were fed to larvae and adults, which significantly suppressed the corresponding gene expressions after 24-h feeding treatment. These RNAi treatments resulted in significant mortalities, in which the dsRNA treatments at ∼2,000 ppm specific to vATPase-A or vATPase-B allowed complete control efficacy near 100% mortality in 7 days after treatment. To prevent dsRNA degradation by the digestive proteases during oral feeding, dsRNAs were formulated in a liposome and led to an enhanced mortality of the larvae and adults of F. occidentalis. The dsRNAs were then sprayed at 2,000 ppm on F. occidentalis infesting hot peppers in a greenhouse, which resulted in 53.5–55.9% control efficacy in 7 days after treatment. Even though the vATPases are conserved in different organisms, the dsRNA treatment was relatively safe for non-target insects owing to the presence of mismatch sequences compared to the dsRNA region of F. occidentalis. Conclusion: These results demonstrate the practical feasibility of spraying dsRNA to control F. occidentalis infesting crops.

Orthotospovirus tomatomaculae (tomato spotted wilt virus, TSWV) is transmitted by the western flower thrips, Frankliniella occidentalis. Epoxyoctadecamonoenoic acids (EpOMEs) function as immune-suppressive factors, particularly in insects infected by viral pathogens. These oxylipins are produced by cytochrome P450 monooxygenases (CYPs) and are degraded by soluble epoxide hydrolase (sEH). In this study, we tested the hypothesis that TSWV modulates the EpOME level in the thrips to suppress antiviral responses and enhance its replication. TSWV infection significantly elevated both 9,10-EpOME and 12,13-EpOME levels. Following TSWV infection, the larvae displayed apoptosis in the midgut along with the upregulated expression of four caspase genes. However, the addition of EpOME to the viral treatment notably reduced apoptosis and downregulated caspase gene expressions, which led to a marked increase in TSWV titers. The CYP and sEH genes of F. occidentalis were identified, and their expression manipulation using RNA interference (RNAi) treatments led to significant alternations in the insect’s immune responses and TSWV viral titers. To ascertain which viral factor influences the host EpOME levels, specialized RNAi treatments targeting genes encoded by TSWV were administered to larvae infected with TSWV. These treatments demonstrated that NS_S expression is pivotal in manipulating the genes involved in EpOME metabolism. These results indicate that NSs of TSWV are crucially linked with the elevation of host insect EpOME levels and play a key role in suppressing the antiviral responses of F. occidentalis.

Parthenogenesis is not uncommon in thrips. This asexual reproduction produces males (arrhenotokous) or female (thelytokous). Only females are found in the onion thrips (Thrips tabaci Lindeman 1889) infesting Welsh onion (Allium fistulosum) in several areas of Korea. To determine the reproduction mode of T. tabaci, thrips infesting Welsh onion were collected from different localities in Korea. Cytochrome oxidase I (COI) sequences were then assessed. Results showed that all test local populations had signature motif specific to a thelytokous type. These COI sequences were clustered with other thelytokous populations separated from arrhenotokous T. tabaci populations. In a laboratory test, individual rearing produced female progeny without any males. These results support that Korean onion thrips infesting Welsh onion have the thelytokous type of parthenogenesis. Local thrips populations exhibited significant variations in susceptibility to chemical and biological insecticides. Random amplified polymorphic DNA (RAPD) analysis indicated genetic variations of local populations. However, the genetic distance estimated from RAPD was independent of the actual distance among different local populations. These results suggest that genetic variations of T. tabaci are arisen from population subdivision due to asexual thelytokous reproductive mode.

Acrobeloides nanus is a cosmopolitan, parthenogenetic soil nematode that is widely distributed across various terrestrial environments, including forests, sand dunes, and agricultural lands. In Korea, this nematode was first isolated from soil collected from a potato farm. It has been used as a biological indicator for monitoring contamination caused by divalent metals such as copper and zinc. In this study, A. nanus was isolated from the soil collected from a cucumber farm, and its identity was confirmed using both morphological and molecular markers. Spray-induced gene silencing using double-stranded RNA (dsRNA) represents a promising new strategy for pest control. Here, we tested a spraying dsRNA that would specifically suppress the target genes in A. nanus. Three genes (Pat-10, Unc-87, and vATPase-B) were targeted, and their expression levels were assessed following treatment with their corresponding dsRNAs. The dsRNAs were sprayed onto the nematode diet. As the concentration of dsRNA increased, the expression levels of the target genes were significantly reduced, leading to notable nematode mortality. However, nematicidal activity varied among the three different dsRNAs. To practically assess these dsRNAs under field conditions, the dsRNAs were applied to the soil containing the nematodes by a drenching application. Significant mortality was observed in treatments with dsRNAs targeting vATPase-B or Pat-10, but not with dsRNA targeting Unc-87. To enhance nematicidal activity in soil, the dsRNAs were formulated with chitosan. This formulation significantly improved the stability of dsRNAs under soil conditions and increased their control efficacy against A. nanus. This study suggests that the drenching technique offers an effective strategy to the control of soil-dwelling nematode pests affecting agricultural crops.

Hemocytes (insect blood cells) consist of several morphological types and perform a variety of physiological processes, including immune responses. However, we do not know how many cell types are functionally differentiated in hemocytes or how they perform independent physiological processes. To address this fundamental question, we analyzed hemocyte transcripts with a single-cell RNA-sequencing (scRNA-Seq) technique. The hemocytes were collected from larvae of a lepidopteran insect, Spodoptera exigua, in which four different hemocyte types were morphologically recognized. scRNA-Seq discriminated 24 hemocyte clusters based on the transcripts of each cell. The clusters were separated into seven functional groups predicted from the top three highly expressed and annotated genes in each cluster: active protein synthesis (12 clusters), apoptosis (5 clusters), melanization (2 clusters), modulating cell shape (6 clusters), antimicrobial peptide production (9 clusters), calcium homeostasis (8 clusters), and cell repairing (1 cluster). Signal components of Toll/IMD immune pathways were variably expressed among the clusters. Biosynthetic genes associated with oxylipin immune mediators were specifically expressed among the clusters. Immune effectors such as melanization and apoptosis were expressed in specific hemocyte clusters. Specifically expressed genes that discriminate hemocyte types were used to develop fluorescence in situ hybridization (FISH) markers. In addition, five new hemocyte groups, which were not among the four known hemocyte types in the transcript profile, were identified and discriminated with their specific FISH markers. The hemocyte clusters underwent dynamic changes upon immune challenge. A trajectory analysis using the transcriptome suggests at least three different hemocyte differentiation pathways. These results indicate that the hemocytes of S. exigua are functionally highly differentiated and exhibit a dynamic transition in response to environmental changes.